ipedex instrumentation training modules

8/9/2019 Ipedex Instrumentation Training Modules

http://slidepdf.com/reader/full/ipedex-instrumentation-training-modules 1/919

July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION



Page 1

TABLE OF CONTENT

INSTRUMENT MODULES

VOLUME 1

MODULE No. 1 - INSTRUMENTATION 1

Unit 1 IntroductionUnit 2 Pressure MeasurementUnit 3 The Pressure TransmitterUnit 4 Flow MeasurementUnit 5 Measurement of LevelUnit 6 Practical Tasks

VOLUME 2


Unit 1 Measurement of TemperatureUnit 2 Temperature TransmitterUnit 3 The ControllerUnit 4 Valves and ActuatorsUnit 5 Practical Tasks


Unit 1 Converters and PositionersUnit 2 RecordersUnit 3 Indicators and Combined UnitsUnit 4 Hazardous Areas and Intrinsic Safety

MODULE No. 4 - INDUSTRIAL ELECTRONICS 1

Unit 1 The Electrical CircuitUnit 2 Series and Parallel CircuitsUnit 3 Electromagnetic PrinciplesUnit 4 Basic Electrostatics and the CapacitorUnit 5 The Inductor, Capacitor and DCUnit 6 AC PrinciplesUnit 7 Common Electrical SymbolsUnit 8 Practical Tasks



Page 2


Unit 1 Basic Semiconductor TheoryUnit 2 Diode ApplicationUnit 3 The Controlled Diode

Unit 4 TransistorUnit 5 Practical Tasks

VOLUME 3


Unit 1 Digital MathematicsUnit 2 Introduction to Digital SystemUnit 3 Logic Gates, Flip-Flops, Counters and RegistersUnit 4 Memories and Clocks

Unit 5 Multiplexers, Decoders and DisplaysUnit 6 Digital / Analog & Analog / Digital ConvertersUnit 7 The ComputerUnit 8 Introduction to Data TransmissionUnit 9 Practical Tasks

MODULE No. 7 - INSTRUMENT WORKSHOP

Unit 1 Practical Tasks

MODULE No. 8 - P&ID’s

Unit 1 General SymbolsUnit 2 Reading P&IDUnit 3 Practical Tasks

MODULE No. 9 - CONTROL SYSTEMS 1

Unit 1 IntroductionUnit 2 Practical Tasks

MODULE No. 10 - PROCESS CONTROL FUNDAMENTAL

Unit 1 Basic Control Theory

Unit 2 Tuning a ControllerUnit 3 Introduction to DCS and PLCUnit 4 Honeywell TDC 3000 DCSUnit 5 Foxboro IA DCSUnit 6 Practical Tasks

MODULE No. 11 - INSTRUMENT CRAFT PRACTICE



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 1

INSTRUMENTATION 1



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 1

INSTRUMENTATION 1

UNIT No. 1

INTRODUCTION



July 1999- Rev.0 Page 1/9

TRAINING MANUALINSTRUMENTATION

UNITS IN THIS COURSE

UNIT 1 INTRODUCTION TO INSTRUMENTATION

UNIT 2 PRESSURE MEASUREMENT

UNIT 3 THE PRESSURE TRANSMITTER

UNIT 4 FLOW MEASUREMENT

UNIT 5 MEASUREMENT OF LEVEL

UNIT 6 PRACTICAL TASKS

M o d u l e

N o .

1 : I n s t r u m e n t a t i o n 1

U n i t N o .

1 - I n t r o d u c t i o n





TABLE OF CONTENTS

Para Page

1.0 COURSE OBJECTIVE 3

1.1 INTRODUCTION 4

1.2 INSTRUMENT WORK 4

1.3 BASIC DEFINITIONS 5

1.4 PROCESS CONTROL 7

1.4.1 Open Loop (Manual Control) 7

1.4.2 Closed Loop (Automatic Control) 8

1.5 CONCLUSION 9

M o d u l e

N o .


U n i t N o .






1.0 COURSE OBJECTIVE

The student will be able to

• Explain in general terms the duties of an instrument technician.

• Define the following terms used in instrumentation.

⇒ Instrument

⇒ Instrumentation

⇒ Process and process variable.

⇒ Controller

⇒ Correcting unit.

⇒ Transmitter and transmission signal

⇒ Process loop and plant

⇒ Indicate and record.

• Explain in general terms the purpose of instrumentation to obtain automaticcontrol.

M o d u l e

N o .


U n i t N o .






1.1 INTRODUCTION

The aim of this unit is to introduce the subject of instrumentation, the duties of theinstrument technician and what is meant by instrumentation and control.

1.2 INSTRUMENT WORK

The duties of an instrument technician fall into five main areas.

• Repair and calibration of instruments which measure physical quantities, forexample pressure, level, gas concentration, acidity, etc.

• Repair and calibration of instruments that indicate and record the value of a

physical property. For example, temperature (thermometer), pressure(gauges), chart recorders, etc.

• Repair and calibration of the final control element, for example a controlvalve, electric heater, thermostat, etc.

• Repair and calibration of a complete control system, for example the controlof a gas turbine, steam plant, etc.

• Carry out preventive maintenance programs.

The instruments in use are very varied, depending on how old the installation is.They may be air (pneumatic), liquid (hydraulic) or electric / electronic in operation.The way the information is shown or recorded may be simple, like a clock orthermometer. It may use the latest information technology to display information ona personal computer screen (video display unit).

The aim of this course is to introduce all the above topics. Real working instrumentsystems will have to be learnt in the plant after this course is over.

M o d u l e

N o .


U n i t N o .






1.3 BASIC DEFINITIONS

Instrumentation uses a lot of words which need to be explained. Before we can talkabout instrumentation and process control you need to understand the followingwords.

• Instrument - Any device for measuring, indicating,controlling, recording and adjusting aphysical or chemical property e.g. flow,pressure, acidity, weight, gasconcentration, etc.

• Instrumentation - A complete set of instruments used tocontrol a process, e.g. refining, oil/gas

production, LNG, LPG, etc.

• Indicator - A device which shows a measured value tothe operator.

• Recorder - A device which continuously recordsmeasurements, either electronically or onan ink chart. It is used to show productionfigures, etc.

• Process Loop - A group of instruments used to control asingle process variable e.g. pressure, flow,

level, etc.

• Process - The operator's word for a manufacturingunit e.g., refining, liquefying gas, etc.

• Measured Variable - The value of the property being controlledor Process Variable by a single process loop e.g. pressure(MV) flow, or Process Variable level, etc.

• Desired Value - The value required by the operator.or Set Point (S P)

• Error Signal - The difference between the measured(ES) variable and the set point should be zero

for good control.

• Controller - A device, either pneumatic or electrical /electronic, which adjusts the error signal tozero.

M o d u l e

N o .


U n i t N o .






• Correcting Unit - A device which works on the command of(Final Control the controller. It is used to adjust the

Element) measured value to obtain a zero errorsignal, e.g. control valve, etc.

• Transmission - A method of standardising signals sentfrom various parts of the plant.

• Transmitter - A device which takes a measurement andchanges it into a standard signal.

• Transducer - A device which changes one form ofenergy to another; particularly fromelectrical to pneumatic.

M o d u l e

N o .


U n i t N o .






1.4 PROCESS CONTROL

1.4.1 Open Loop (Manual Control)

Figure 1-1 The Open Loop

Figure 1-1 shows what is called OPEN LOOP or MANUAL control. The process istemperature control. The indicator is a thermometer. The correcting unit is the gascontrol valve. The controller is the operator who uses his own judgement to keep

the water temperature constant.

Manual control has its uses as it is cheap to install and maintain, and simple tooperate. However, it is very seldom used in industry because:

• The operator must remain in position at all times.

• It cannot be used if the operator is placed in a dangerous area.

• The process changes faster than the operator can react.

• A mistake by the operator can have dangerous results.

These problems are avoided by using automatic control (closed loop). The job ofthe instrument technician is to make sure that this type of control operates correctly.

Modern household appliances now use automatic control to make work easier. Forexample:

• Refrigerators and water heaters use automatic temperature control.

• Washing machines use automatic heating and water control.

M o d u l e

N o .


U n i t N o .






1.4.2 Closed Loop (Automatic Control)

Figure 1-2 Simple Automatic Control.

Figure 1-2 shows a simple automatic controller. The boiler now has the loop closedand no operator is required. The following items are added.

The temperature transmitter (T.T) which measures (senses) the temperature of the

hot water and changes it to a standard signal.

A signal line from the transmitter to the controller, the signal may be eitherpneumatic or electrical.

A controller which keeps the temperature of the hot water at a position set by theoperator (set point)

The controller adjusts the correcting unit (automatic control valve) using an outputsignal line similar to the input line from the transmitter.

The controller may provide alarm signals to alert the operator if the system fails. It

may also shut off the gas if the water starts to boil.

M o d u l e

N o .


U n i t N o .






1.5 CONCLUSION

This unit has introduced instrumentation and control. The following units will explain

in detail how control loops are made and operated. We will start with themeasurement (sensing) and transmitting unit.

There are many process variables in the petroleum industry but most of thesevariables fall into four main groups: pressure, flow, level, and temperature. We willlook at these groups.

Most of the other process variables (e.g., density, gas concentration, acidity, etc.)will be explained when needed during a specialist analyser course.

M o d u l e

N o .


U n i t N o .




July 1999- Rev.0

Page 1/22









M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -

P r e s s u r e m e a s u r e

m e n

t



July 1999- Rev.0

Page 2/22


TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 PRESSURE 4

2.2.1 Pressure and Liquids 4

2.2.2 Pressure and Gases 5

2.2.3 Pressure Units 5

2.2.4 Absolute, Gauge and Atmospheric Pressure 9

2.2.5 Example 1 10

2.3 PRESSURE MEASURING DEVICES 11

2.3.1 The Manometer 11

2.3.2 The Well Manometer 12

2.3.3 The Inclined Limb Manometer 12

2.3.4 The Bourdon Tube Pressure Gauge 13

2.3.5 Special Adaptation of the Bourdon Tube. 14

2.4 BELLOWS 16

2.5 DIAPHRAGMS AND CAPSULES 17

2.5.1 Diaphragms 17

2.5.2 Capsules 18

2.6 ELECTRICAL METHODS 19

2.6.1 The Piezo Electric Effect. 19

2.6.2 The Capacitive Cell 20

2.6.3 The Strain Gauge 21

2.6.4 Vibrating (Resonant) Wire 22

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 3/22




• Define pressure

• Explain the action of pressure on liquids and gases.

• Explain the terms

⇒ Absolute pressure

⇒ Gauge pressure

⇒ Vacuum pressure

⇒ Differential pressure

• State the standard pressure units used in the petrochemical industry.

• Carry out simple pressure unit conversions using standard tables.

• Draw and explain the operation of the following pressure sensors

⇒ Manometer

⇒ Bourdon tube

⇒ Bellows

⇒ Diaphragm and capsules.

⇒ Strain gauge

⇒ Capacitance element

⇒ Vibrating (resonant) wire

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 4/22


2.1 INTRODUCTION

The aim of this unit is to define pressure and describe the common devices used tomeasure it.

2.2 PRESSURE

2.2.1 Pressure and Liquids

PRESSURE (P) is defined as the FORCE (F) applied divided by AREA

Figure 2-1 Pressure on a Liquid

Figure 2-1 shows a force (F) applied to a piston pressing on a liquid in a cylinder.The liquid is considered INCOMPRESSIBLE and the pressure of the liquid onthe-walls of the cylinder is the same in all directions. This gives the formula:

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 5/22


2.2.2 Pressure and Gases

Figure 2-2 Pressure on a Gas.

Figure 2-2 shows a force (F) applied to a piston pressing on gas in a cylinder. Thegas is COMPRESSIBLE. The volume of the gas will decrease until the pressure ofthe gas on the walls of the cylinder equals the pressure applied by the piston.

2.2.3 Pressure Units

There is no agreed standard for pressure measurement in the petrochemicalindustry. Some companies use IMPERIAL UNITS (USA), some useINTERNATIONAL STANDARD METRIC UNITS (ISO) and some use both. Theinstrument technician must understand both systems and be able to change fromone to another.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 6/22


CONVERSION

1 psi = 6895 Pa

The Pascal is a very small unit so the KILOPASCAL (kPa) is often used. A biggerunit is the bar. This is the most common ISO unit.

CONVERSION

100 kPa = 1 bar

Note : On very old installations the kilogram per centimetre square is still used.For all general purposes.

1 kg/cm2

= 1 bar.

Very small pressures are measured using the height of a column of liquid. Theliquids used most are water (H2O) and mercury (Hg). The ISO unit for this type ofmeasurement is 1 mm height of mercury. This is called the torr.

CONVERSION VALUES:

1 inch H20 0.03613 psi 249.1 Pa = 0.002491 bar

1 mm H20 0.004122 psi 9.8907 Pa = 0.000098907 bar

1 inch Hg 0.4912 psi 3386 Pa = 0.03386 bar

1 mm Hg 0.01934 psi 133.3 Pa = 0.001333 bar

An instrument workshop usually has a conversion table for easy reference. You canphotocopy the conversion table on the next page and use it for easy reference.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 7/22


PRESSURE CONVERSION TABLE

C 0 L U M N

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 8/22


Using the conversion table

The rows (across) and columns (up and down) are complementary, so that you can

convert bar to psi or psi to bar.

The bar row gives 14.50 in the psi column

The psi row gives 0.0689 in the bar column

The following examples are given to show how the table is used.

Examples

(a) Convert 50 psi to bar

1 psi = 0.0689 bar

50 psi = 50 x 0.0689 = 3.445

50 psi = 3.445 bar

(b) Convert 120 kPa to psi

1 Pa = 1.450 x 10-4

120 kPa = 1.450 x 10-4 X 120 x 103 17.5

120 kPa 17.5 psi

(c) Convert 150 mmHg to bar

1 mmHg = 1.333 x 10-:3

150 mmHg = 150 x 1.333 x 10*3 = 0. 2000

150 mmHg = 0.2 bar

(d) Convert 50 in H20 to psi -

1 in H20 = 0.03613

50 in H20 = 50 x 0.03613 = 1.8065

50 inH20 = 1.8065 psi

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 9/22


2.2.4 Absolute, Gauge and Atmospheric Pressure

The price of oil or gas depends on the quantity (mass) of the product. The quantity

of oil or gas in a given volume depends on the pressure. For this measurement,absolute pressure must be used.

Absolute Pressure

This is the pressure above a total vacuum (there are no particles of matter in a totalvacuum)

Gauge Pressure

This is the pressure measured by a gauge. The pressure above the pressure of thesurrounding atmosphere.

Atmospheric Pressure

The pressure of the air all around you. This is not constant it depends on things likethe weather and the altitude of the plant.

The equation linking the above pressures together is:

Absolute pressure = Gauge pressure + Atmospheric pressure

(A. P) (G. P) (Atmos)

Because atmospheric pressure can vary a STANDARD ATMOSPHERIC pressurehas to be used. This is normally 1.013 Bar or 14.70 psi.

Gauge pressure is written as psig. Absolute pressure is written as psia.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 10/22


2.2.5 Example 1

Question :

A pressure gauge indicates 11.4 psi. Find the absolute pressure if the atmosphericpressure is 14.65 psi.

Solution:

AP = GP + ATMOS

AP = 11.4 + 14.65 = 26.05

Absolute pressure = 26.05 psi

Example 2

Question

A pressure gauge reads 3.5 psi vacuum. Find the absolute pressure if theatmospheric pressure is 14.73 psi.

Solution:

Vacuum pressures are normally given as gauge pressures below atmosphericpressure (zero gauge). That is a negative gauge pressure.

AP = - GP + ATMOS

AP = - 3.5 + 14.73 = 11 .23

3.5 psi vacuum pressure = 11.23 psi absolute pressure

A simple diagram is shown below as an example.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 11/22


2.3 PRESSURE MEASURING DEVICES

2.3.1 The Manometer

The manometer is a simple device to measure small amounts of pressure. Itconsists of a glass tube of a fixed diameter. It is bent into a U shape with (vertical)sides. The sides are next to a scale. The manometer is filled with a liquid e g wateror mercury

Figure 2-3 The Manometer

Figure 2-3 shows the construction -of the manometer and its uses.

• Absolute Pressure

One side is sealed with a vacuum above the liquid in the manometer. Anunknown pressure is applied to the other side (limb) which forces the liquiddown. The difference in height (H) of the liquid column will give the unknownabsolute pressure. For example, a 9 inch difference, with water as the liquid,will give an absolute pressure of 9 x 249.1 = 2242 Pa.

•

Gauge Pressure

One side is left open to the atmosphere. An unknown pressure is applied tothe other side. This pressure will force the liquid in the tube down. Theheight of the liquid gives the gauge pressure of the unknown pressure.

• Differential Pressure

If unknown pressures are applied to both sides the difference in level (H) willgive the difference (differential) between the two in absolute pressure.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 13/22


2.3.4 The Bourdon Tube Pressure Gauge

The Bourdon tube gauge is the most common pressure indicator in the

petrochemical industry. It shows the pressure in a clear, simple way.

Figure 2-6 above shows a typical Bourdon gauge. It consists of the following parts:

• The Bourdon tube itself. This is a metal tube shaped like a "C". It has an

oval cross sectional area. It is sealed at one end. The sealed end is free tomove.

• A linkage and pinion to turn the pointer.

• A scale to indicate the pressure.

Operation

When a pressure is applied to the inside of the tube it will try to straighten. Theclosed end (the tip) will move and the linkage moves the pinion which moves thepointer. The movement of the pointer shows how much pressure is applied to theBourdon tube.

Bourdon gauges come in all shapes and sizes and can measure from about 0-15psig (0-1 bar) to 0-10,000 psig (0-700 bar) depending on the stiffness of thematerial used.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 14/22


Materials

In the low ranges the Bourdon tube is made from copper alloys In the medium

ranges it is made from mild steel or stainless steel. In the high ranges it is madefrom high tension steel. Calibration adjustments

The calibration adjustments on a Bourdon gauge depend on the manufacturer.However, some basic rules are:

• Zero adjustment is done either by moving the pointer to zero on the scale orby moving the scale so that zero is under the pointer.

• Span adjustment (the maximum reading of the scale) is set by adjusting thelinkage in the geared sector and pinion.

• Linearity is adjusted by changing the length of the linkage (not often addedon modern gauges) Remember to follow the manufacturer's instructionswhen you calibrate a gauge.

2.3.5 Special Adaptation of the Bourdon Tube.

The Spiral Bourdon Tube.

Figure 2-7 Spiral Bourdon Tube

Figure 2-7 shows a spiral Bourdon tube (Foxboro). It is used to indicate lowpressures. When pressure is applied the spiral unwinds and the free end moves toindicate the pressure. The construction and calibration of this type of gaugedepends on the manufacturer. The handbook must be used.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 15/22


The Helical Bourdon Tube

Figure 2-8 Helical Bourdon Tube.

Figure 2-8 shows a helical Bourdon tube (Foxboro). This is usually used to indicatehigh pressures. When pressure is applied the helix unwinds and the free end movesto indicate the pressure applied. The actual construction and calibration depend onthe manufacturer and the manual must be used.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 16/22


2.4 BELLOWS

Bellows are tubes with thin walls, made of brass, stainless steel, etc. The thin walls

are corrugated. This improves their ability to expand and contract. When pressure isapplied (either to the outside or the inside), the corrugated walls expand or contract.This movement is used to indicate pressure. Bellows units are usedin variousways. The three most common methods are shown below:

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 17/22


An example of a differential bellows unit (Foxboro) is shown in Figure 2-9. The air ispumped out of one bellows (evacuated). This makes a vacuum so that when apressure is applied to the other bellows unit absolute pressure is measured.

Figure 2-9 Differential Bellows Unit (Foxboro)

2.5 DIAPHRAGMS AND CAPSULES

2.5.1 Diaphragms

A diaphragm is a stiff corrugated disc which is flexible under pressure. A singlediaphragm is often used as a seal to protect a gauge from corrosive liquids. A

typical example is given in Figure 2- The Schaffer gauge.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 18/22


Diaphragms are also used to make high pressure bellows (a diaphragm stack). Anexample is shown in Figure 2-11.

Figure 2-11 A Diaphragm Stack

2.5.2 Capsules

Capsules are made of two diaphragms welded onto a metal ring and filled with afluid. Different mechanical and electrical methods are used to show the differentialpressure across the capsule. Figure 2- shows a Foxboro capsule used in apneumatic differential pressure transmitter.

Figure 2-12 The Capsule (Foxboro)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 19/22




July 1999- Rev.0

Page 20/22


2.6 ELECTRICAL METHODS

The old mechanical methods of detecting pressure are slowly being replaced by

electrical methods. Electrical methods are more accurate and cheaper. Thefollowing notes give a simple explanation of the principle involved.

2.6.1 The Piezo Electric Effect.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 21/22


2.6.2 The Capacitive Cell

This method is used by Rosemount in their sensing capsules. A cut away section of

this capsule is shown in Figure 2-13.

Figure 2-13 The Capacitive Cell

When a differential pressure is applied across the capsule the silicone oil will bepressurised more on one side than the other. The sensing diaphragm will moveaway from one fixed capacitor plate and nearer to the other. The difference in

capacitance between A and B, and B and C, is measured by an electronic amplifier.This measurement shows the differential pressure.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 22/22


2.6.3 The Strain Gauge

The strain gauge is a resistor which has been deposited onto a flexible bar. As the

bar is bent the resistor will change in length and thus its resistance. The changes inresistance are detected by a Wheatstone bridge and electronically changed to apressure signal. A strain gauge is shown in Figure 2-14. This method is used byHoneywell in their electrical transmitters.

Figure 2-14 Simplified Strain Gauge Capsule

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t



July 1999- Rev.0

Page 23/22


2.6.4 Vibrating (Resonant) Wire

The vibrating wire is the operating method used by Foxboro in their pressure

transmitters. Figure 2-15 shows the basic construction.

Operation:

Figure 2-15 The Vibrating Wire

The frequency of vibration of a wire depends on its tension. The tension of thevibrating wire is changed by the pressure applied to the diaphragm. The electronicsunit has a driving coil (D.C) to make the wire resonate and a sensing coil (S.C) tomeasure the resonant frequency. This changes the pressure applied to thediaphragm into an electrical signal output.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n i t N

o .

2 -


m e n

t





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 THE FLAPPER-NOZZLE 4

3.3 THE PNEUMATIC RELAY 6

3.4 THE PNEUMATIC TRANSMITTER 7

3.5 THE PNEUMATIC SIGNAL LOOP 11

3.6 THE AIR PRESSURE REGULATOR 12

3.7 THE ELECTRICAL PRESSURE TRANSMITTER 14

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -

T h e p r e s s u r e

t r a n s m

i t t e r






The student will be able to:

• Explain the operation of a simple flapper nozzle.

• Explain the function of a pneumatic relay.

• Using a diagram, name the parts of a typical pneumatic transmitter.

• Explain the need for the feedback (positioning) bellows.

• State the standard signals produced by a pneumatic transmitter.

• Draw the layout of a typical electrical transmission loop.

• State the standard signals produced by an electrical transmitter

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





3.1 INTRODUCTION

The previous unit (Unit 2) explained the basic devices used to measure and indicatepressure. This unit will describe the methods used to convert the pressuremeasurement to an instrument signal for the controller.

3.2 THE FLAPPER-NOZZLE

The flapper-nozzle is the primary device for all pneumatic instruments which converta measurement to a pneumatic signal. Figure 3-1 shows the layout of the device.

Figure 3-1 The Flapper-Nozzle

Operation:

The air supply input (20 psi (1 .4 bad) passes through a restrictor (small hole). Itthen goes out of the nozzle or down the air signal output line. If the flapper is placedagainst the nozzle, no air can escape through it. So, the air signal output shows fullpressure. If the flapper is pulled away from the nozzle, most of the air flows out ofthe nozzle, so the air signal output pressure is very small. The back pressure outputsignal depends on how near the flapper is to the nozzle. A simple graph of theoutput pressure (P) against flapper distance (X) is shown below.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





The graph is linear (straight) over the distance A B. This reflects only a fewmillimetres of travel of the flapper. This part of the curve is used to convert a

change in a measured value connected to the flapper into an output signal. Therestrictor increases the speed of operation. The small volume (V) can changepressure quickly before the air supply can pass through the small hole in therestrictor.

The change in output pressure due to flapper movement is very small. It must beenlarged (amplified) using a device called a PNEUMATIC RELAY.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





3.3 THE PNEUMATIC RELAY

Different manufacturers make pneumatic relays in different ways. However, they allwork on the same principle. A simplified explanation of this device is given in Figure3-2.

Figure 3-2 The Pneumatic Relay

Operation

The output pressure from the flapper-nozzle goes to the top of the diaphragm. Thediaphragm Moves down against the controlling spring and opens the ball valve. Theair supply now enters the area under the diaphragm and goes into the output.

At some point, the pressure from the air supply under the diaphragm will equal thepressure above. The diaphragm moves up and the ball valve closes and they holdmomentarily at that pressure. If the flapper-nozzle pressure increases, the ball valvewill open and hold momentarily at the new higher output pressure. If the pressureon the diaphragm decreases, the ball valve stays closed and the output signal fallsas air escapes through the vent. When the output pressure has fallen enough theball valve opens again to maintain the output at the new lower pressure. This kind ofrelay is called a continuous bleed device because it controls the output signal

pressure by slowly venting the air supply all the time.

The standard amplified signal from the relay is:

(a) 3 -15 psi imperial (b) 0.2 -1 bar ISO.

Remember that these standards are not the same. The control system can work on(a) or (b). It must never work on a mixture of the two standards.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





3.4 THE PNEUMATIC TRANSMITTER

There are many different types of pneumatic pressure transmitters. However, theyare not used much nowadays.

One of the few types still in use is the Foxboro type 11 . This is' shown below as anexample of the pneumatic transmitter.

Figure 3-3 The Pneumatic Pressure Transmitter

Figure 3-3 shows the basic design of a Foxboro pressure transmitter.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





Operation:

• The process pressure to be measured and transmitted as a standard signal

is applied to a diaphragm capsule.

• The pressure moves the capsule. This movement is applied to one end of aforce bar pivoted about the diaphragm seal.

• The force bar moves the flexible connector. The connector pulls the flapperto and from the nozzle.

• The back pressure from the nozzle is amplified by the relay. This gives thestandard output signal.

The system is not stable. The flapper will go either full on or full off. So a feedbackbellows is added. The output signal goes to the bellows. The bellows applies a forceto the range rod in opposition to the force bar. The system balances to give anoutput signal which depends on the position of the range wheel.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





Figure 3-4 Balancing action

Figure 3-4 shows the balancing action of the transmitter. The movement of theflapper is the pressure applied times B over A (B:A). The feedback movement is theoutput pressure times the ratio D:C.

The ratio B:A is fixed but D:C can be changed by the range wheel. If the D:C ratio islarge the feedback is small. This makes the range larger.

Calibration Adjustments

•

When there is no pressure (zero gauge), the zero spring, which sets theforce on the range rod, is adjusted for a 3 psi or 0.2 bar output signal.

• With the maximum pressure (range) applied, the range wheel is adjusted togive 15 psi or 1 bar output signal.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





Note Figure 3-3 shows a gauge pressure transmitter. This transmitter caneasily be adapted to measure differential pressure. This is done by

adding an extra input to the diaphragm capsule as shown below. Theforce bar now moves according to the differential pressure applied.Remember the device must be connected correctly to the high andlow pressure connections. It will not read correctly if it is connectedthe wrong way round.

ABSOLUTE PRESSURE APPLIED TO THE CAPSULE

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





3.5 THE PNEUMATIC SIGNAL LOOP

Figure 3-5 The Pneumatic Signal Loop

Figure 3-5 shows a block diagram of the pneumatic signal loop :

• The process line to the pressure transmitter (usually 3/8" or 1/4" stainlesssteel tubing) has an isolation valve and a drain valve so it can bedisconnected.

• The pressure transmitter has an air supply set at 20 psi. This comes throughthe air pressure regulator from the main air supply (usually about 100 psi).

• There is a signal line (usually 1/4" stainless steel tubing) which transmits thesignal (3-15 psi) to the receiver in the controller.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





3.6 THE AIR PRESSURE REGULATOR

The air pressure regulator is a simple device. It is used to lower the main instrumentair supply of a plant to a pressure suitable for an air operated instrument; eg, atransmitter, control valve, etc.

Normally, each air operated instrument has its own regulator. So an. air regulator isone of the most common devices in the plant. There are various manufacturers ofair regulators, eg, Masoneilan and Fisher. However, they all work in much the sameway. The example given is manufactured by Fisher (see Figure 3-6).

Figure 3-6 The Air Pressure Regulator

Operation:

• The main air supply is connected to the IN port. Air passes into the inletchamber at the bottom of the regulator.

• Air passes through the filter which removes dirt particles in the incoming airwhich may block nozzles etc. It then goes into the valve assembly.

• The valve assembly is moved by the range spring pressing on thediaphragm.

•

The range spring will hold the valve assembly down until the output pressureis high enough to lift the diaphragm (via the air passage shown). At this pointthe small spring in the valve assembly closes the valve.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





• Air is allowed to pass through a hole at the centre of the diaphragm and outof the vent. This maintains balanced pressure across the diaphragm.

•

If the outlet pressure is, above the pressure set by the range spring, the airwill go out through the vent above the diaphragm. When the outlet pressureis correct, the valve assembly opens to set the correct pressure.

• If the outlet pressure is below the pressure set by the range spring the valveassembly will stay open until the set pressure is reached.

Note :

• The drain valve should be opened regularly to drain any moisture in the inletchamber.

• Range springs come in various sizes. The most common is from 5-35 psi(0.34-2.4 Bar). This is set to give an output of 20 psi for transmitters, etc.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





3.7 THE ELECTRICAL PRESSURE TRANSMITTER

Electrical transmitters have replaced pneumatic transmitters in most petrochemical

plants. This is because they are cheaper to install and maintain. The transmission ofthe signal is also cheaper and easier to install. This is because an electricaltransmitter has one pair of wires instead of expensive stainless steel signal tubingand air supply lines.

There are three main types of transmitters. They use three kinds of capsules:capacitive (Rosemount), strain gauge (Honeywell) or vibrating wire (Foxboro). Theoutput from the capsule is electronically converted to a STANDARD 4-20 mASIGNAL for transmission to the control room.

An electrical transmitter is calibrated with an instrument screwdriver or pushbuttons. There are two adjustments, zero and span (range).

The calibration and servicing depends on the manufacturer. It must be carried outusing the manual. Modern transmitters have become throw away items. If theycannot be calibrated they are not serviced. They are thrown away and replaced witha new transmitter.

Figure 3-7 below shows, as; an example, a Rosemount electrical transmitter.

Figure 3-7 The Rosemount Electrical Transmitter

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r





Any electrical transmitter uses an electrical series loop and it acts as a variableresistor. The basic diagram of the loop is shown in Figure 3-8.

PLANT CONTROL ROOM

Figure 3-8 The Electrical Series Loop

The power supply provides the EMF around 24V D.C., to drive the series loop. This

loop consists of:

• Two safety barriers(RB) which protect the plant from dangerous voltages inthe case of a fault.

• The transmitter, whose resistance (RT) changes with the measured pressurechanges.

• The controller with a resistance RC. The voltage across the resistanceprovides the signal for the controller electronics.

The current around the circuit (1) will be

RB and 'Rc are constant. So, the current changes as the resistance in thetransmitter (RT) changes.

The system is set so that with zero pressure, the current is 4 mA and 20 mA at themaximum value of the measured pressure.

Note : Both pneumatic and electrical transmitter signals have a live zero. hismeans that a broken circuit can easily be detected

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N

o .

3 -


t r a n s m

i t t e r












M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -

F l o w m e a s u r e m

e n

t





TABLE OF CONTENTS

Para Page


4.1 INTRODUCTION 4

4.2 UNITS OF FLOW 4

4.3 QUANTITY METERS 7

4.3.1 Positive Displacement 7

4.3.2 Velocity Meters (semi-positive displacement) 9

4.4 RATE OF FLOW MEASUREMENT 10

4.4.1 Flow Basics 10

4.4.2 Flow Measurement by Differential Pressure 11

4.4.3 Differential Pressure Devices 15

4.5 VARIABLE AREA METERS 21

4.6 CALIBRATION OF FLOW MEASURING DEVICES 22

4.6.1 Quantity Meters 22

4.6.2 Calibration of Differential Pressure Devices 23

4.6.3 Flow Straighteners 23

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t







• Explain the difference between total flow and rate of flow measurements.

• Explain the difference between mass and volume flow units.

• Use volumetric and mass conversion tables.

• Explain with the aid of a sketch how positive displacement flow meters work.

• Explain with the aid of a sketch how velocity flow meters work.

• Explain, with the aid of sketches, the use of a pipe restriction to produce adifferential pressure for rate of flow measurement

• Sketch the following rate of flow measuring devices and list their advantagesand disadvantages.

The orifice plate

The Venturi

The Venturi - nozzle.

The nozzle

• Sketch a variable area meter.

• State the calibration procedures that can be used to calibrate flow meters.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.1 INTRODUCTION

The aims of this unit are:

i) to explain the measurement of liquid flow

ii) describe devices used to measure liquid flow.

4.2 UNITS OF FLOW

Figure 4-1 Flow Measurements

Figure 4-1 shows a tanker being loaded from a storage tank. The amount of oilloaded must be accurately measured to know how much it costs (fiscal purposes).The total flow (quantity) of oil into the tanker can be measured in two ways:

• by volume, in barrels or cubic meters.

•

by mass, in metric or imperial tons (the international standard for oil/gastransfer).

For control purposes the rate of flow (how fast the ship is loaded) is also measured.Rate of flow units can also be given in either volumetric or mass units.

For example

• Rate of flow by volume (volumetric)

Barrels / Hour

Cubic Feet / Min.

Cubic Meters / Sec. M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





• Rate of flow by mass

Tons/ Hour Kilograms / Sec. Pounds / Min. The petrochemical industry uses manydifferent units and-there is no common standard. The following list gives some ofthe units and their conversion.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.3 QUANTITY METERS

There are two basic methods used to measure quantity (total flow)

(a) Positive displacement.

(b) Velocity meters (semi-positive displacement)

4.3.1 Positive Displacement

The simplest form of positive displacement meter is the gasoline (petrol) pump. Itwill release an exact amount of gasoline in either imperial gallons or litres. A simplediagram to show its operation is shown in Figure 4-1

Figure 4-2 Reciprocating Piston Meter

Operation:

When the piston is at the bottom of its stroke (see Figure (A)) the slide valve opensthe inlet vent to the bottom of the cylinder. The liquid (petrol) flows into the cylinderbelow the piston and pushes the piston upwards. As the piston rises the liquid in thetop half of the cylinder is pushed through the outlet vent into the outlet pipe. Whenthe piston is at the top of its-stroke the slide valve closes the outlet at the top of thecylinder and opens the inlet vent. At the same time the slide valve opens the outletvent at the bottom of the cylinder and closes the inlet (see Figure (B)). The pressureof the liquid coming into the top of the cylinder pushes the liquid at the bottom of thecylinder into the outlet pipe. The amount of liquid coming out of the cylinder duringeach stroke is measured. Each time the piston makes a stroke a meter connectedto the top of the piston indicates how much liquid has been delivered.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





The oil industry's positive displacement meter is the sliding vane meter. It can beused for measuring large quantities of liquid flow; eg, oil being loaded onto a tanker.

A typical example is shown in Figure 4-3.

Figure 4-3 The Sliding Vane Meter

Operation:

This meter consists of a rotating drum with four sliding vanes (long blades) setinside it. The vanes move around a cam which is fixed in the centre of the drum.The liquid flowing through the meter pushes the vanes round with the drum. As thevanes rotate with the drum the cam pushes them in and out against the measuringwall. As the vanes are pushed against the measuring wall, they trap a measuredvolume of liquid between the drum and the measuring wall. Each revolution of thedrum will measure 4 lots of the measured volume. The number of revolutions of thedrum is counted and displayed. This gives the total flow passing through the meter.The calibration nut is used to adjust the side of the measurement chamber so that

the volume of liquid passing through the meter can be measured exactly.

Note: A static liquid chamber is added so that there is no differential pressureacross the measurement wall.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.3.2 Velocity Meters (semi-positive displacement)

The sliding-vane type meter is not used much nowadays because it is slow. Mostloading meters for shipping are now of the velocity type. The velocity metermeasures the speed of the flow and works out the volume of flow using calibrationfigures.

Figure 4-4 The Turbine Meter

Operation:

The velocity (speed) at which the rotor turns depends on the flow rate. The pick-upcoil gets a pulse induced for every rotation. The number of pulses is counted by anelectronics unit. This unit displays the total quantity of flow.

Note : In the oil/gas industry these two quantity meters are only for liquidmeasurements.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.4 RATE OF FLOW MEASUREMENT

The previous two quantity meters are used to calculate how much oil the customerpays for, so they must be extremely accurate. A modern turbine meter will measureto within ± 0.1 % of the true reading. Devices for measuring the rate of flow do notneed to be so accurate. They are used mainly to give a flow signal to a controller.

4.4.1 Flow Basics

Figure 4-5 Flow in a Pipe

Figure 4-5 shows the flow of a fluid (gas or liquid) down a pipe. The flow isproduced by the differential pressure across the ends of the pipe (P1-P2). The wallsof a pipe are not perfectly smooth. The frictional force at the walls will cause thefluid to go slower at the edge than at the centre.

This leads to two different types of f low.

• LAMINAR FLOW

The fluid flow rate is slow and the velocity of the wavefront down the pipe ismuch higher in the centre of the pipe than at the edges.

• TURBULENT FLOW

The fluid flow rate is high and the velocity of the wavefront is the sameacross the pipe. However, the flow is a little slower at the edges against thewall.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





The velocity lines on the diagram are called STREAMLINES. Engineers assume thestreamlines are straight and parallel to each other.

4.4.2 Flow Measurement by Differential Pressure

Figure 4-6 Flow through a Restriction

Figure 4-6 shows the flow of a fluid through a closed pipe full of liquid or gas. It hasa restriction in the pipe.

Because there is a restriction, there is a difference between the pressure at thecentre of the restriction (position Y) and the pressure in the normal pipeline (positionX)

The difference in pressure between the centre of the restriction and the normalpipeline pressure (P1-P2) is proportional to the square root of the flow rate (Q)

given as an equation.

or

CD is called the "coefficient of discharge". We can get this from tables. It dependson what is used to make the restriction.

Note :- Pl + P2 is often written as DP (Differential Pressure) or AP (Delta P).

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





The above equation means that the measured DIP has to be square rooted beforethe flow rate can be calculated. Modern electronic transmitters do this automatically

and a linear 4-20 mA signal for flow rate is produced. The older pneumatic systemsproduce a flow rate indication by using a square root scale or chart. A typical squareroot scale is shown below.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





Theory

Bernoulli said "The sum of the kinetic energy (velocity energy) and pressure energyat any point in a closed pipe is a constant", i.e. the sum of these two types of energyis always the same.

This is true if the pipe is horizontal and the temperature of the fluid does notchange.

As the fluid flows through the restriction, it gets faster (the velocity increases). Thisis because FLOW = VELOCITY x AREA. If the area is smaller, the velocity isbigger. So, the pressure must fall and from the diagram;

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





CD is called the "coefficient of discharge". We can get this from tables. It dependson what is used to make the restriction.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.4.3 Differential Pressure Devices

There are many devices used to make a restriction in a pipeline so that rate of flowcan be measured. The design of each device is fixed by either ISO or ISA(instrument Society of America) standards. There are standard tables which areused to calculate flow. In the petroleum industry engineers assume the flow isturbulent. However, you can get tables for laminar flow if you need them. A fieldtechnician will only need to calibrate the differential pressure transmitter. Anengineer will give a technician the figures he needs to do this. Some of the morecommon devices are given below together with their uses.

• The Orifice Plate

Figure 4-7 The Orifice Plate and Tappings

Figure 4-7 shows an orifice-plate fitted into a pipeline to make a differentialpressure. The orifice plate is a flat disc with a hole in it shaped as shown. The frontedge is sharp and the back edge is chamfered. The fluid is squeezed as it passesthrough the hole and has a maximum velocity at a point called the VENACONTRACTOR.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





Taps (holes) are drilled into the pipeline and a differential pressure transmitterconnected across the orifice plate. The differential pressure is measured. The

square root of the differential is used to produce a flow signal which is proportionalto the flow.

Standard tables are produced for the tapping places as shown.

The position of the hole in the plate depends on the fluid being measured. Thediagram below shows typical plates and their uses.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





All orifice plates must be made to an exact standard to fit the reference tables. Atypical example is given below for a D and D/2 tap fitting.

Figure 4-8 Dimensions for a D and D/2 orifice plate fitting

The advantages and disadvantages of an orifice plate.

Advantages

1. Simple in operation

2. No moving parts

3. Reliable for a long time

4. Not expensive

Disadvantages

1. Square root relationship

2. 2.Difficult to install

3. 3.Range of measurement small. Operator has to change plate (hole size) tochange the range.

Note : The orifice plate is the only suitable device when measuring high gas flowrates.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





• THE VENTURI

This is a very expensive device. It is used when the energy of the flow is so low thatthe restriction could stop the flow (low pressure loss). The diagram below shows atypical Venturi with its pressure tappings (see Figure 4-9).

Figure 4-9 The Venturi

The advantages and disadvantages of the venturi.

Advantages

1. Simple in operation

2 . Low pressure loss

3. Can be used with liquids that contain solids

4. Reliable for a long time

5. No moving parts

Disadvantages

1. Expensive

2. Square root relationship

3. Poor range. Designed for one job only

4. Difficult to install

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





• NOZZLES

These are a compromise between the orifice plate and the venturi. They arecheaper than a venturi but have a high pressure loss. They are moreexpensive than an orifice plate, but have lower pressure loss. A fewexamples are shown below.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





• PRESSURE LOSS GRAPH

The graph below (see Figure 4-10) shows how much pressure is lost whenthese devices are used. The Y axis shows the hole size and the X axisshows the percentage of pressure lost. This shows the advantages of theventuri over the orifice plate. It also shows how the nozzle is between thetwo.

Figure 4-10 Pressure Loss Graph

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.5 VARIABLE AREA METERS

These are simple devices used to indicate small rates of flow. They are used by anoperator out in the field. Typical uses are:

• In seal oil and lubrication oil flow lines on large rotating machines; eg, dieselengines and gas compressors.

• In cooling water lines for machines and processes.

Figure 4-11 shows a variable area meter (Rotameter).

Figure 4-11 The Rotameter

Operation

The Rotameter is fitted vertically into the flow line. The flow of the fluid is frombottom to top through the cylinder. The cylinder increases in area from bottom totop. With no flow, the float is at the bottom (position A). When the flow increases,the pressure makes the float rise. It will rise to a position where the flow pressure onthe float equals the weight of the float, (position B). If the flow gets faster there ismore pressure on the float and it will rise higher (position C). The flow rate indicateddepends on the size of the device. It is pre-calibrated by the manufacturer. Theoperator reads the flow rate from the transparent scale using the top of the float as

a marker.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.6 CALIBRATION OF FLOW MEASURING DEVICES

4.6.1 Quantity Meters

The only way to calibrate a flow quantity meter accurately is to use a standardvolumetric measure. This is easy when the volumes are small. A gasoline pump ischecked by a standard measure; eg, a 10 litre can. When you fill the can the meteron the pump should read 10 litres. This method is impossible when you need tomeasure thousands of gallons per minute. The system used to check large liquidvolumes is called a PROVER LOOP. A simple diagram of the system is shown inFigure 4-12.

Figure 4-12 The Prover Loop

The prover loop consists of a calibrated section of pipe. A tightly fitting rubber ball(sphere displacer) is pushed through the pipe by the flow of a liquid which must bemeasured. Two detector switches mark the travel of the ball. The computer worksout the volume measured by the travelling ball and compares this measurementagainst the volume measured by the meter. The four way valve lets the operatorsend the ball in both directions through the calibrated section of pipe. This meansthat the ball can be passed a number of times to make sure the meter is checked

accurately.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t





4.6.2 Calibration of Differential Pressure Devices

In order to calibrate the differential pressure transmitter, the field technician usesfigures given by the design engineer. For control purposes, the actual flow need notbe exact. However, the movement of large amounts of gas can only be checkedusing an orifice plate. The true volume, at standard pressure, is worked out by aspecial programme on a computer. This work is done by a specialist called ametering engineer.

4.6.3 Flow Straighteners

All flow measuring devices which use a restriction need a streamlined flow. Flowmeasuring devices must be placed away from things which disturb the flow; eg

elbows, control valves, etc. If this is not possible then the flow is streamlined by flowstraighteners. These are groups of small pipes placed in the pipe line as shown inFigure 413.

Figure 4-13 Flow Straighteners

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U

n i t N o .

4 -


e n

t



July 1999- Rev.0

Page 1/20









M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 2/20


TABLE OF CONTENTS

Para Page


5.1 INTRODUCTION 4

5.2 THE DIP STICK 4

5.3 THE DIP TAPE 5

5.4 THE SIGHT GLASS 5

5.5 FLOATS 6

5.5.1 The Simple Float 6

5.5.2 Industrial Float Systems 7

5.6 HYDROSTATIC TANK GAUGING (HTG) 9

5.6.1 Introduction 9

5.6.2 Offset Datum Lines 12

5.6.3 Wet Legs 13

5.7 DISPLACERS AND LOCAL LEVEL CONTROL 14

5.8 LEVEL SWITCHES 17

5.9 AIR BUBBLE METHOD 19

5.10 OTHER METHODS OF LEVEL MEASUREMENT 20

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 3/20




• Explain the use of a dip stick and dip tape.

• Sketch a typical sight glass installation.

• Explain, with the aid of a diagram, typical level measurements using floats.

• Explain, with the aid of diagrams, hydrostatic tank level measurement.

• Explain, with the aid of a sketch, the operation of a typical buoyancy level

transmitter.

• Sketch typical float operated level switches.

• Explain, with the aid of a diagram, the bubbler method of levelmeasurement.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 4/20


5.1 INTRODUCTION

The aim of this unit is to introduce the measurement of level and the devices usedin its indication, measurement and control

5.2 THE DIP STICK

The dip stick shown in Figure 5-1 is the only true measurement of level. It is stillused by operators and ships' captains to check that the instrumentation whichmeasures the level of a liquid in a tank is correct.

The dip stick is a long calibrated ruler. The depth of the liquid in the tank isindicated by a WET mark when the stick is removed. It's the same principle as

checking the oil level of a car. Because there may be rubbish at the bottom of thetank the level may be taken from a bottom level datum line. A datum line is a baseline from which things can be measured. There is also a top datum line which isused to measure the space above the liquid (the ullage).

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 5/20


5.3 THE DIP TAPE

Figure 5-2 Dip Tape

The dip tape shown in Figure 5-2 is a development of the dip stick for finding thelevel in large tanks. The tape is run out until the weight touches the bottom of thetank. It's then pulled up. The wet mark on the tape indicates the depth of the liquid.

Note : The dip stick / tape is no good if the liquid does not leave a WET mark. Anexample of this type of liquid is mercury.

5.4 THE SIGHT GLASS

This is the level indicator used by operators in the plant. The device is connected tothe side of a vessel and the level is seen by looking through the glass. A highpressure sight glass is shown in Figure 5

Figure 5-3 High Pressure Sight Glass M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 6/20




July 1999- Rev.0

Page 7/20


There are many different types of sight glasses. A single glass tube is strongenough for low pressures. For high pressures you need a reinforced glass tube with

a steel case, as shown in Figure 5-3. Most industrial sight glasses can be cleanedon site by closing the isolating valves, draining the tube via valve D and roddingthrough valve A. Good sight glasses also have an automatic shut-off valve. Thisoperates if the glass breaks. It stops all the liquid draining out of the vessel.

High pressure sight glasses have very specific instructions about how they are puttogether and taken apart. You must use the manufacturer's manual. A highpressure sight glass should never be used again because re-tensioning will makethe glass break.

5.5 FLOATS

5.5.1 The Simple Float

Figure 5-4 Simple Float Indicator

Figure 5-4 shows a simple float level indicator. It is still used by water departmentsand on chemical tanks on older oil platforms. It is cheap to install and easy tooperate.

Operation

The float and counter weight are connected together by a wire on pulleys. Thesystem is in balance with the float on the surface of the liquid. If the level rises, thefloat rises and the counter weight falls to the new balance point. If the level falls thecounter weight rises. The counter weight has a pointer which indicates the level ona scale on the outside of the tank. The scale shows "full" when the pointer is at thebottom and "empty" when it is at the top. The scale can be very large so that, forexample, water tower levels can be seen from the ground.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 8/20


5.5.2 Industrial Float Systems

The simple float is not very accurate and can be very difficult to read. If the surfaceof the liquid has waves then the float starts to swing. This problem is solved byfitting special devices inside the tank as shown in Figure 5-5.

Figure 5-5 Tank Constructions

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 9/20


• Guide wire system (Figure a)

This is the cheapest system. The float; C, is held in place by wires; B. Theseare fixed to the bottom by a concrete block; A, and tightened by a spring; D.

The float is connected by a wire (to the indicating unit K) via a pulley system(FGF) and pipe (1) supported on brackets (J). The indicating unit is thecounter-weight and the level is indicated by a mechanical counter.

• Still pipe system (Figure b and c)

This is a more expensive method but it is more accurate. The float iscontained inside a still pipe (a steel pipe with holes in it). The level inside thepipe doesn't move so it gives very accurate measurements of level. Figure b

shows the older mechanical indication method. Figure c shows the modernmethod (Entis-Enraf). The system is electronically controlled and the levelmeasurement is sent as an electronic signal to the control room.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 10/20


5.6 HYDROSTATIC TANK GAUGING (HTG)

5.6.1 Introduction

Many of the modern oil storage tank facilities (tank farms) use hydrostatic tankgauging to indicate the level in a tank. HTG is good because there is no equipmentinside the tank. It is cheaper to install and maintain than float installations.

BASIC PRINCIPLE

The higher the level of a liquid in a tank, the higher the pressure on the bottom ofthe tank. The nearer the outlet is to the bottom of the tank, the greater the pressureand the further the flow stream will reach. Figure (a) shows this effect.

The pressure on the bottom of a tank only depends on the level of the liquid in the

tank. Figure (b) shows this effect. No matter what the shape of the tank, thepressure (P) at the bottom of the tank is the same.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 11/20


Proof :

The force on the bottom of the tank is the weight of the liquid.

WEIGHT OF LIQUID = VOLUME x DENSITY x GRAVITY

but VOLUME = AREA (A) x HEIGHT (H)

Therefore

WEIGHT OF LIQUID =

AREA (A) x HEIGHT (H) x DENSITY (p) x GRAVITY (g)

but PRESSURE = FORCE(WEIGHT AREA

)

AREA AREA-x HEIGHT x DENSITY x GRAVITY

PRESSURE (P) = HEIGHT(H) x DENSITY (p) x GRAVITY (g)

or

P = pgH

This equation shows that the pressure at the bottom of a column (level) of liquiddoes not depend on the shape of the container.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 12/20




July 1999- Rev.0

Page 13/20


Hydrostatic Tank Gauging (HTG) uses the pressure of a column of liquid tomeasure the level. The diagram below shows the basic layout of the system (see

Figure 5-6)

Figure 5-6 Hydrostatic Tank Gauging

Theory

P1 = Pressure above the liquid level

P2 = Pressure at inlet to differential pressure transmitter

P2 = P1 + Pressure of liquid above the datum line.

The pressure of the column of liquid above the datum line is given by the formula:

P = Density x Gravity x Height

Gravity is a constant and providing the density of the liquid does not change then

P = KH where K is a constant

and P2 = P1 + KH

The differential pressure (DP) across the transmitter is

P2 - P1 = P1+ KH - P1

DP = KH

This means that the DP transmitter signal gives a direct indication of level.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 14/20


5.6.2 Offset Datum Lines

The above system works well if the transmitter can be placed at the same level as

the datum line. This is often not possible and the offset (the difference between thelevels of the datum line and the transmitter) must be allowed for. The diagrambelow illustrates the problem, (see Figure 5-7)

(a) Transmitter Below Datum Line (b) Transmitter Above Datum Line

Figure 5-7 Transmitter Off-set

In figure (a) the transmitter is lower than the datum line. 'V' is the difference inheight between the transmitter and the datum line. So, the transmitter will give thewrong reading, it will be 'V' units too high.

Figure (b) shows the transmitter above the datum line. In this case the transmitterwill give a level which is 'V' units too low, because the pressure of the liquid abovethe transmitter is less than the pressure of the liquid above the datum line.

Differential pressure transmitters have special units added to allow for the aboveproblem. They are called elevation/depression units. These units move the zero toallow for the height difference between the transmitter and the datum line.Manufacturers use different methods for elevation/depression. The manual must be

used when setting up a differential pressure transmitter on a tank.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 15/20


5.6.3 Wet Legs

Figure 5-8 Wet Legs

Some liquids produce heavy vapours. These vapours may condense to liquid in thepipe between the differential pressure cell and the top of the tank. This condensatecan cause the transmitter to give the wrong reading. To stop this, the pipe is filledwith a known liquid (eg glycol). This is called the "Wet Leg The differential pressuretransmitter is adjusted using the elevation/depression units to offset the pressurecaused by the height of the liquid in the wet leg (P3).

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 17/20


The displacer unit is connected to both the vessel and the control valve. This makesa self contained local control loop as shown in Figure 5-10

Figure 5-10 Self-contained Local Control Loop

Operation

• The weight of the displacer changes as the level rises or falls in thedisplacer housing.

• The displacer hangs on the torque tube via the connecting rod.

• The changing weight of the displacer makes the torque tube twist or untwist.

• The twisting motion of the torque tube moves a flapper against a nozzle.This sends a control signal to the pneumatic control valve.

• The pneumatic control valve opens or closes to keep the level constant atthe set point.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 18/20


Theory

A displacer works on "Archimedes Principle"

"The weight of a body immersed in a liquid depends on the weight of the volume ofliquid displaced". In other words , if the displacer displaces a volume of liquid whichweighs 1 kg, the displacer will seem to weigh 1 kg less than it weighs when it's notin the liquid.

Figure 5-11 Simple Example of Archimedes Principle

Figure 5-11 shows a simple example of Archimedes' principle. In 'A, the scaleshows 3 Kg weight. The displacer weighs 3 kg. In 'B' the displacer has displaced avolume of water which weighs 1 kg. So, the scale shows a weight of 2 kg i.e. 3 kgminus 1 kg for the liquid displaced.

The diameter of the container and displacer are kept constant. So, the weight losson the displacer is directly proportional to the liquid level in the displacer housing. If

the displacer weighs less then the torque tube is twisted less. The amount thetorque tube twists depends on the level of liquid in the displacer housing.

Note :- The weight of the liquid displaced is given by the formula

Weight = Volume x Gravity x Density

So, changing the density of the liquid in the vessel means the Level-Trol must berecalibrated.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 20/20


Figure 5-13 Float Operated Mercury Switch

Figure 5-13 shows a typical electrically operated level switch. The mercury bottlehas three connections, the mercury (a good conductor) acts as the switch to changeover the contacts. The switch is operated magnetically, the two different positionsbeing clearly shown. When the level is high the switch is in one position. When thelevel falls, the switch is in the other position.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 21/20


5.9 AIR BUBBLE METHOD

The air bubble method is one of the oldest and simplest methods used to indicate

and or transmit a signal. The diagram below shows a simplified layout of themethod (see Figure 5-14).

Figure 5-14 Liquid Level Measurement by Air Bubbler Method

Operation

• An inert gas (air or nitrogen) is passed down the bubbler tube. There is justenough gas pressure for the bubbles to appear when the liquid is at themaximum level in the vessel.

• When the vessel is full the pressure gauge or transmitter will read amaximum back pressure equal to the hydrostatic head (H), (the pressure ofthe liquid above the zero level).

• At the zero level the back pressure will be zero and the gauge or transmitterwill read zero.

• The back pressure between zero and maximum levels is proportional to theliquid level in the vessel. The pressure gauge or transmitter can becalibrated to indicate the liquid level.

• The gas pressure is adjusted by the regulator to give a steady flow of gasdown the bubbler tube. The gas flow is indicated on the Rotameter.

• This method can be very accurate. A modern differential pressuretransmitter, open at one side, can easily be calibrated to give a span of 0-6"H20

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l



July 1999- Rev.0

Page 22/20


5.10 OTHER METHODS OF LEVEL MEASUREMENT

In this unit we have introduced some common methods of measuring level used on

most installations.

There are many other methods using various types of high technology. These willbe special for only one or two installations. You will have to learn them on the job. Afew examples are:

(a) Radar, ultrasonic, gamma and infrared detectors.

(b) Capacitive sensors.

(c) Resistive sensors.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

5 -

M e a s u r e m e n

t o f

l e v e

l












M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





TABLE OF CONTENTS

Para Page

PRACTICAL TASK 1 3

PRACTICAL TASK 2 14

2.1 PNEUMATIC TRANSMITTER 14

2.2 ELECTRICAL TRANSMITTER 15

PRACTICAL TASK 3 25

3.1 PNEUMATIC DIFFERENTIAL PRESSURE TRANSMITTER CALIBRATION 25

3.2 ELECTRICAL DIFFERENTIAL PRESSURE TRANSMITTER CALIBRATION 26

PRACTICAL TASK 4 36

PRACTICAL TASK 5 39

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





PRACTICAL TASK 1

CALIBRATION OF PRESSURE GAUGES

INTRODUCTION

The practical work you will do during this task will show you the common methodsused to calibrate a pressure gauge. The test equipment used to calibrate the gaugemay not be the newest type but it will work in the same way as newer equipment.New pressure sensors (e.g. piezoelectric, strain gauge etc.) are quickly changingthe way test equipment is made from mechanical to electronic display.

The particular test equipment used by an operating company must be learnt on site.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





THE PRECISION GAUGE AND TEST BENCH.

Most instrument workshops calibrate site gauges using a test bench fitted withprecision gauges. This is a much quicker method than using a dead weight test andaccurate enough for field calibration (± 1 %).

The precision gauges are calibrated regularly by a dead weight tester. This ensuresthat the gauges stay accurate. A typical example of gauge calibration using aprecision gauge is shown in Figure PT 3.

Figure PT 3 Gauge Calibration Using a Precision Gauge.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





PRACTICAL TASK 1

CALIBRATION PROCEDURE

1. Do not apply any pressure to the gauge. Set the pointer to read zero on thescale.

2. Apply the full range pressure to the gauge. Adjust the linkage so that thepointer is at the maximum reading on the scale, (full scale deflection).

3. Reduce the pressure to zero and check that the pointer reads zero on thescale. Adjust the pointer if necessary.

4 Repeat steps (2) and (3) until both readings are correct.

5. If the gauge has a linearizing adjustment, set the applied pressure to 50% ofthe maximum scale reading. Adjust the linearizing adjustment so that thepointer reads at 50% of the maximum scale reading.

6. Check the gauge reads correctly at 0, 50% and maximum reading. You mayneed to adjust the gauge many times before the gauge is correct. You mustbe patient and careful.

7. When step (6) is completed, write down the reading on the gauge for theapplied pressure readings. A calibration table is provided.

8. Draw a graph of the gauge readings and the applied pressures (increasingand decreasing).

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





9. The graph you get will look something like the graph shown above. Theshaded area shows the hysterisis of the gauge (the hysterisis is thedifference between rising and failing pressure readings). The biggestdifference between the true reading and the gauge reading tells you howaccurate the gauge is.

Hysterisis is caused by friction and wear on the operating mechanism. If thegauge is not accurate enough, the mechanism cannot be replaced. In thiscase the gauge is thrown away.

You must decide if a gauge is accurate enough. If it is not accurate enoughyou must say so.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION TABLE

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





APPLIED PRESSURE

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





2.2 ELECTRICAL TRANSMITTER


1. Connect the inlet pressure connection to the calibrated pressure supply (e.g.dead weight tester, pressure bench etc.).

2) Connect the 24V DC supply to the terminal board connections. Use themanual of the particular transmitter you have. A series load resistor may berequired.

3) You may need to use an ammeter in series to measure the 4 20 mA signal.

However, most transmitters have a standard resistor (1 Ω) so 4 - 20 mV is

measured instead. This is a more accurate measurement. The manual willtell you what to do.

The setting zero and the span of the operating range will be given by theinstructor.

4) Produce a calibration graph of output range (4 - 20 mA) against inputpressure range. This will show if the transmitter is still linear. Check it iswithin the stated accuracy.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION TABLE (BAR)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION TABLE (mA)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION GRAPH

INPUT / OUTPUT RELATIONSHIP OF THE PNEUMATIC PRESSURETRANSMITTER

OUTPUT PRESSURE (psi)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION GRAPH

INPUT / OUTPUT RELATIONSHIP OF THE PNEUMATIC PRESSURETRANSMITTER

OUTPUT PRESSURE (bar)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION GRAPH

INPUT / OUTPUT RELATIONSHIP OF AN ELECTRICAL PRESSURETRANSMITTER

OUTPUT PRESSURE (mA)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION GRAPH

INPUT / OUTPUT RELATIONSHIP OF AN ELECTRICAL PRESSURETRANSMITTER


M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





PRACTICAL TASK 3

CALIBRATING A DIFFERENTIAL PRESSURE TRANSMITTER

INTRODUCTION

Calibrating a differential pressure transmitter is much more difficult than calibratinga pressure transmitter. This is because the pressures are very small. A modern D.P.transmitter can have a calibration range of 0-5" H20 gauge. You can calibrate thiswith a manometer but normally a very low pressure test gauge is used. Theequipment used in the lab is called a 'wally box'. This is a special pressure test kitmade by Wallace and Tiernan. The 'wally box' is not used much now because of itssize. Modern hand-held electronic devices (e.g. DRUCK) are becoming popular.

3.1 PNEUMATIC DIFFERENTIAL PRESSURE TRANSMITTER CALIBRATION

1. Connect the calibrated pressure supply to the HIGH inlet pressure. Leavethe LOW pressure inlet connection open.

2. Connect the air supply port to the 20 psi (1.4 bar) supply.

3. Use a pressure gauge to cover the range 0 - 20 psi (0 - 1.4bar). Connect itto the output port.

4. Using the manufacturer's manual set up the differential pressure transmitterto values given by the instructor.

5. Use the results to draw a calibration curve in the same way as for a pressuregauge. Ensure the device gives a linear output of 3-15 psi (0.2-1 bar). Checkits accuracy is within specification. Remember: 3-15 psi is not equivalent to0.2-1 bar. Calibrate using either 3-15 psi or 0.2-1 bar.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION TABLE (12sil

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION TABLE (bar)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION TABLE (MA)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION GRAPH

INPUT / OUTPUT RELATIONSHIP OF THE PNEUMATIC DIFFERENTIALPRESSURE TRANSMITTER

OUTPUT PRESSURE (psi)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION GRAPH

INPUT / OUTPUT RELATIONSHIP OF THE PNEUMATIC DIFFERENTIALPRESSURE TRANSMITTER

OUTPUT PRESSURE (bar)

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION GRAPH

INPUT / OUTPUT RELATIONSHIP OF AN ELECTRICAL DIFFERENTIALPRESSURE TRANSMITTER


M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





PRACTICAL TASK 4

CALIBRATION OF A LEVEL TRANSMITTER (LEVEL-TROL)

INTRODUCTION

Figure PT4 Fisher Level Trol

The level transmitter to be calibrated is a Fisher level-trol. This uses a displacertype level detector. A layout of the device is shown in Figure PT 4.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





The calibration adjustments are inside the transmitter housing. They are shown inFigure PT 5.

FIGURE PT 5 Transmitter With Cover Removed .

The instruction manual for calibrating this transmitter is difficult to understand.There is only one instruction manual for controller or transmitter operations foreither level (gas/liquid), interface (liquid/liquid), or density. The following procedurewill only help you calibrate a level transmitter (gas/liquid). The basic procedure usedin this calibration is the same for any type of displacement level transmitter. It ispossible to calibrate this unit using weights instead of the sensor (displacer unit).However, this is seldom done. You will calibrate the transmitter using water to setthe required level. This is the normal workshop method. Remember the finalcalibration must be done on the job. This final calibration depends on where thetransmitter is fitted (e.g. gas/oil, oil/water interface, etc.). You will have to learn thiscalibration on site.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





CALIBRATION PROCEDURE (WET TYPE)

Figure PT 6 Calibration Wet Type

Pre-checks

1. Set the air supply pressure to 20 psi on the supply gauge Adjust the airregulator if required.

2) Set the S.G dial to 1.

3) Put the zero adjustment dial to read zero.

Calibration

1. When the water level is below the bottom of the displacer, set the zeroadjustment. Check that the output gauge reads 3 psi.

2. Fill the displacer housing with water until the level is above the displacer. Adjust the S.G. dial until the output reads 15 psi.

3) Repeat steps (1 ) and (2) until both are correct.

4) Raise the water level until it reaches the centre line (L) The output pressureshould be 9 psi.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





PRACTICAL TASK 5

CALIBRATING A PRESSURE SWITCH

Figure PT 7 The Pressure Switch

Figure PT-7 shows a typical pressure switch. The inlet pressure is applied to thebottom of the operating piston. This piston is forced upwards by the inlet pressureagainst the range spring. The tension of the range spring can be adjusted so that itis compressed at a certain pressure. When this pressure is reached the operatingpin will hit the trip button on the micro-switch and change it over. The normally opencontacts (NO to C) will become closed and the normally closed contacts (NC to C)will open. The pressure at which the micro-switch changes over is set by adjustingthe trip setting nut. This nut adjusts the tension of the range spring (e.g. if the nut isturned clockwise the trip pressure will be higher).

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s





1) Connect the pressure switch to the workshop air supply via a hand pressure

regulator and test gauge, as shown in the diagram.

2) Use an Ohmmeter to check that the switch contacts are as indicated; NOand NC.

3) Connect the Ohmmeter to the normally open contacts. The meter shouldread "open circuit". Adjust the hand pressure regulator to increases thepressure to the switch until the contacts change over. The meter should nowread "short circuit". Note down the pressure reading on the sheet provided.This pressure is the switch setting for a "rising" pressure.

4) Increase the pressure to the switch to it's maximum rating. Slowly reduce the

pressure to the switch until the switch changes over from closed to normallyopen again. Note down this pressure reading on the sheet provided. Thispressure is the switch setting for a "falling" pressure.

5) From the readings you have taken work out the pressure difference betweenthe rising and falling pressure settings. This is called the "dead band" of theswitch.

6) The maximum dead band is usually stated by the manufacturer. The switchis unserviceable if the maximum dead band is more than the manufacturer'srecommendation.

7. On job site the pressure switch will be set for either a falling or a risingpressure. This is stated on the maintenance sheet.

8) After you have completed steps 1 to 7 and the instructor is sure that youhave understood what you have done, try setting the switch to anotherposition. You do this by adjusting the trip setting nut. The instructor will givea setting value for either rising or falling pressure inputs.

M o

d u

l e

N o .

1 :

I n s

t r u m e n

t a t i o n

1

U n

i t N o .

6 -

P r a c

t i c a l t

a s

k s






UNIT 1 MEASUREMENT OF TEMPERATURE

UNIT 2 TEMPERATURE TRANSMITTER

UNIT 3 THE CONTROLLER

UNIT 4 VALVES AND ACTUATOR


M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 TEMPERATURE SCALES 4

1.2.1 The Absolute Scale 4

1.2.2 Examples 5

1.3 EXPANSION TYPE THERMOMETERS 6

1.3.1 Liquid In Glass Thermometers 6

1.3.2 Filled Systems 8

1.3.3 Solid Expansion Types. 10

1.3.4 Thermostats 10

1.3.5 Bi-metal Strip Thermometers 11

1.4 ELECTRICAL METHODS OF TEMPERATURE MEASUREMENT 12

1.4.1 The Resistance Temperature Detector (RTD) 12

1.4.2 The RTD Detector: The electrical circuit 15

1.4.3 The Thermocouple 16

1.4.4 The Thermistor 20

1.4.5 Radiation Temperature Detectors (Pyrometers) 21

1.5 THERMOWELLS 24

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





1.3 EXPANSION TYPE THERMOMETERS

Most materials expand as they get hotter. An expansion type thermometer uses theexpansion of a material to indicate temperature. There are several different types.

1.3.1 Liquid In Glass Thermometers

Figure 1-2 The Thermometer

The "liquid in glass" thermometer is the most common of all thermometers. It hasindustrial, domestic and medical uses.

The instrument workshop uses these devices as a basic standard for calibration

purposes. A good quality device is accurate to 0.1°C.

The thermometer, (see Figure 1-2) consists of a glass tube (the stem) which has avery small but uniform bore (hole). At the bottom of this stem there is a thin, walledglass bulb. The bulb holds much more liquid than the stem. The bore in the stem issealed under a vacuum so that there is no air in the system. The system works bydifferential expansion. The liquid expands over 20 times more than the glass whenthe bulb is heated.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





1.3.2 Filled Systems

Liquid in glass thermometers are not strong enough for plant use so in industry thebulb and stem are made of steel. The bulb and stem are completely filled with theexpansion liquid under pressure. The indicator is a spiral Bourdon tube, or apressure cell (strain gauge) which gives an electronic signal. Figure 1-3 show thethree basic systems.

Figure 1-3 Filled Systems

The steel bulb, stem and indicator (Bourdon tube) are completely filled underpressure with either; a liquid, eg. mercury, a gas, eg. freon or a vaporising liquid,eg. methyl chloride. Each system works in the same way. The system is totally filledto provide a constant volume. Expansion of the fluid in the tube is converted to apressure. This pressure expands the Bourdon tube which moves the pointer on thescale.

Note: The capillary (the stem) can be many meters long so that theindicator can be placed in a control room away from the fluidtemperature being measured.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





Applications:

Filled systems are still used to indicate temperature particularly in places wherethere is no electrical supply. They are normally of the liquid filled type, to provideenough power to drive a "C" type Bourdon tube. The usual operating range is about

300°C. Gas and vapour filled systems are not used much as indicators becausethey have a short range and no driving power. However, they are used a lot intemperature control, eg. In air conditioning and refrigeration. A filled system is usedto drive a pneumatic temperature transmitter. A typical example of this is theFoxboro type 12. This will be discussed in the next unit.

Ambient Temperature Compensation:

Filled system thermometers can be inaccurate if the capillary tube is long and the

atmospheric (ambient) temperature around the capillary changes a lot from night today. Accurate filled system thermometers use a dummy Bourdon tube and capillaryto compensate for ambient temperature changes. This method is shown in Figure 1-4

Figure 1-4 Ambient Temperature Compensation for a filled System

Thermometer

The dummy Bourdon tube and capillary are exactly the same as the measurementsystem. Any ambient temperature changes causes both the dummy andmeasurement system to move the pointer the same amount, but in oppositedirections. So, the ambient temperature errors are cancelled.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





1.3.3 Solid Expansion Types.

These devices use a solid instead of a fluid to measure or control temperature. The

simplest form is the thermostat used to automatically control the temperature of awater heater. This device uses the expansion differential between brass and invar.

1.3.4 Thermostats

Figure 1-5 The Simple Rod Thermostat

Figure 1-5 shows a simple rod thermostat. The brass tube expands a lot as it getshotter but invar expands very little . When the liquid is cool the brass does notexpand so the switch is closed and the electric heater heats the water. When thewater reaches the set temperature the brass tube has expanded enough to pull theinvar rod away from the switch. This opens the switch and breaks the circuit. Theelectric heater will stay disconnected until the brass tube contracts enough to closethe switch again. Normally the thermostat and heater are together in one unit. Thetemperature at which the switch is opened can be adjusted by changing the tension

of the spring which closes the switch. Thermostats are not very accurate(± 3°C) butthey are long lasting and cheap.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





Construction:

This device indicates temperature by measuring the change in the electrical

resistance of a metal. The sensing element has a platinum coil of about 100Ω

at0°C (the Pt 100) see Figure 1-9. The sensing element is connected to the terminalbox by three wires. The ceramic spacers stop heat moving through the casing (thesheath). The terminal pins have glass to metal seals held in place with glass woolpacking. The output cable connects the sensing head to the electronics unit. Thisconverts the changes in resistance into temperature readings.

Theory of Operation.

When metals get hotter their resistance increases. This increase in resistance isalmost linear. When it's measured it gives an accurate indication of temperature.The sensor is usually platinum because it is stable over a large temperature range

and does not corrode. The normal platinum RTD is 100Ω at 0°C and rises to 138.5Ω at 100°C. The resistance of a Pt 100 at a particular temperature is given in astandard table. These tables must be used when calibrating this device. There is aPt 100 table on the next page.

Note: Cheaper RTD metals (e.g. nickel and copper) are used where thetemperature range is small.

Nickel is used in water heaters and air conditioners.

Copper is used in oil product tank temperature sensing.

Manufacturers provide tables for the calibration of these RTD's.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





TEMPERATURE RESISTANCE VALUES FOR A Pt 100.

Examples of table use.

1) The resistance at 200°C = 175,84Ω

2) The resistance at - 150°C = 39.73Ω

3) The resistance at 560°C = 300.77Ω

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





1.4.2 The RTD Detector: The electrical circuit

Figure 1-9 Simple RTD Detector

The basic circuit (see Figure 1-9) for detecting the resistance of a 3 wire RTD is the

unbalanced Wheatstone bridge. When the RTD is at 0°C (100Ω) the bridge is

balanced so that the display unit reads 0°C As the temperature of the RTD changesthe unbalanced current through the display unit is converted to give thetemperature. The system is calibrated with a decade box (variable resistance unit)

and the Pt 100 tables. For example; place a 335.92Ω resistance value across 1 and

2 when 2 and 3 are joined together and the display unit should read 670°C.

The 3 wire system is used to cancel out unwanted changes in resistance. Thesecan be caused by temperature changes in the air around the connecting leads. This

is called ambient temperature compensation. The leads to 1 and 3 are on oppositesides- of the bridge so that any changes in resistance because of ambienttemperature changes cancel each other out.

For greater accuracy, a 4 wire system of ambient temperature compensation issometimes used. This is shown below (see Figure 1-10). Changes in the resistanceof leads 1 and 2 are cancelled by changes in the resistance of leads 3 and 4.

Figure 1 -10 The 4 Wire System

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





1.4.3 The Thermocouple

Figure 1-11 Seebeck Effect

The thermocouple uses thermoelectric EMF produced by the difference intemperature between two ends of a metal wire. This is an effect discovered bySeebeck, see Figure 1-11. Two different metals are joined to make two different junctions which are held at two different temperatures. The difference between themetals and the difference in temperature between the hot and cold junctions makesa current flow around the circuit. To use this effect you need standard tables whichgive the EMF produced by the temperature difference in various metalcombinations. The EMF is picked up by an electronic amplifier. The indicator ispre-calibrated to show the temperature. The voltage can be checked against thetables, to make sure the indicator is correct.'

Figure 1-12 shows a typical thermocouple temperature measuring system, with a

typical EMF/temperature curve

Figure 1-12 The Thermocouple Thermometer

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





There are many different thermocouples in use. They are classified by letter. Mostmodern thermocouple detecting instruments can use any standard thermocouplepair. However, they must be connected to the correct letter position.

STANDARD THERMOCOUPLES IN USE

-200 to 850 °CLow cost, standardfor general use

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





1.4.5 Radiation Temperature Detectors (Pyrometers)

Radiation temperature detectors (Pyrometers) are non contact devices. They are

used to measure the temperature of something which is difficult to reach by othermeans, (eg. gas turbine combustion chambers). They are also the only way to

measure very high temperatures (above about 1500°C) as all other devices melt.Figure 1-15 shows a typical radiation thermometer.

Figure 1-15 Typical Radiation Thermometer

The heat from the object is focused by lenses onto a sensor. The output from thesensor is electronically processed by the amplifier to give a reading in degrees. Thisdevice can also transmit a signal to the control room if required.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





The sensor is usually a thermopile. A thermopile is a collection of thermocouplesconnected in series to produce a larger millivolt output. A typical thermopile isshown in Figure 1-16. The radiation is focused onto the black painted centre and

the output connected to an electronic amplifier.

Figure 1-16 Thermopile for use in a Radiation Pyrometer

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





1.5 THERMOWELLS

Figure 1-18 Thermowell Installation

The heat in a fluid takes longer to transfer through a thermowell, so changes intemperature take longer to show. Different methods are used to speed up heattransfer. Sometimes the space between the probe and the thermowell is filled with aliquid which conducts heat well. Sometimes the probe is placed in a corrugatedaluminium cover to give a direct metal contact between the probe and thethermoweli. When you change the probe in a thermowell you must replace the newprobe in the same way as the original.

A thermowell is a device fitted in to a flow line so that the temperature of a fluid canbe measured without shutting down the process. A Thermowell is placed in a flowline when the line is built. The thermometer is fitted into the thermowell. A typicalthermowell installation is shown in Figure 1-18.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

1 -

M e a s u r e m e n

t o

f t e m p e r a

t u r e





TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 T HE PNEUMATIC TEMPERATURE TRANSMITTER 4

2.2.1 Foxboro Type 12 Construction 5

2.3 THE ELECTRICAL/ELECTRONIC TEMPERATURE TRANSMITTER 7

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N

o .

2 -

T e m p e r a

t u r e

t r a n s m

i t t e r





2.1 INTRODUCTION

The aim of this unit is to show the construction and operation of two types oftemperature transmitters; the pneumatic temperature transmitter (Foxboro type 12)and the electronic temperature transmitter (Rosemount model 444).

2.2 THE PNEUMATIC TEMPERATURE TRANSMITTER

Figure 2-1 The Foxboro Pneumatic Temperature Transmitter

The most common pneumatic temperature transmitter used in the oil/gas industry isthe Foxboro type 12 (see Figure 2-1). This is used as an example of a typicalinstrument.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N

o .

2 -

T e m p e r a

t u r e

t r a n s m

i t t e r





2.3 THE ELECTRICAL/ELECTRONIC TEMPERATURE TRANSMITTER

One of the most common electrical/electronic temperature transmitters (E.T.T) ismade by Rosemount (Model 444). This is used as an example of a typicalinstrument (see Figure 2-3).

Figure 2-3 Rosemount E.T.T Model 444

The Rosemount Model 444 consists of :

Sensor

The type of sensor depends on the range and application; eg:

• Thermocouple - Type E , J, K, R, S, T.

• RTID - Copper (10Ω), Nickel (120Ω) and PT 100Ω with 2, 3 or 4 wireconnections.

Electronics Unit

This unit has two boards. A RANGE board, depending on the sensor in use and an AMPLIFIER / OUTPUT board which produces the standard 4 - 20mA signal for thecontrol room.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N

o .

2 -

T e m p e r a

t u r e

t r a n s m

i t t e r





Local Temperature Indicator

This unit may or not be included. It provides either a moving coil type display or adigital display. It gives an on site temperature reading to the operator.

Figure 2-4 Typical E.T.T Installation

Figure 2-4 shows a typical installation for this transmitter. The accuracy of thistransmitter is better than any pneumatic instrument. It is ± 0.2% of the calibratedspan.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N

o .

2 -

T e m p e r a

t u r e

t r a n s m

i t t e r











M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r






• The student will be able to:

• Explain the following terms:

measured value

desired value (set point)

error signal

output signal

• Describe the operation of a typical pneumatic controller.

• Describe in general terms, the types of electronic controllers in use.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





changing the computer programme.





The adjustments are:

• Proportional Band (gain). This controls how much the error signal isamplified.

• Integral (reset). This is adjusted to cancel the final error which may be leftafter the proportional action has finished.

• Derivative (rate). This is only used on slow moving loops (for example,temperature). It gives the system a quick start when an error occurs.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





3.3 BASIC CONTROL THEORY

Figure 3-2 Simple Level Control Loop

Figure 3-2 shows a typical level control loop. This loop is for a two stage separatorwhich separates oil from gas in a flow steam from a well head. This basic controlsystem is used to explain the principles of control theory.

The object of good control is to automatically hold the level within safety limits. The

safety limits are set by the system designer as shown in Figure 3-3. The indicatoron the controller shows a percentage % of the minimum and maximum level. Aninstrument technician will set these levels from figures given by the engineer.Typical values are shown in the table (see Figure 3-3).

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





Figure 3-3 Loop Operating Limits

The system is under control if the measured value stays within the high and lowalarm levels. Normally there are two alarm levels. The first is a high/low alarm. Thisallows the operator to take action by going into manual control. In this way he cankeep the process in operation. The second alarm is a high high/low low alarm. If thisalarm is activated it means the system is unsafe and an automatic shutdownoccurs.

The levels which are set for a control system depend on the process. In thisexample ± 5% may be fine. However, in some processes where the quality of theproduct is more important (eg. gasoline) the alarm levels may be less than ± 0.5%.

Quality is becoming more and more important in modern industry. This means thatcontrol must be more and more accurate. For this reason, most modern instrumentsystems are changing from pneumatic to electrical or computer control. Except forthe latest computer control, all systems use the same three control ideas. These areProportional, Integral and Derivative (PID). These three ideas are explained below.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





3.3.1 Proportional (P) Control

Figure 3-4 Proportional Control

Figure 3-4 shows proportional control. The output changes by a proportion (K) ofthe error signal. The error signal is the difference between the measured value (MV)and the setpoint (SP). Therefore:

OUTPUT = K x ERROR SIGNAL

The proportion (K) is also called "gain". It varies from 0.1 to 10 depending on:

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





3.3.2 Proportional + Integral (PI) Control

Figure 3-5 Proportional Integral Control

Figure 3-5 shows the effect of integral action added to proportional control. Integralaction (reset) is added for one reason. It cancels the offset caused by proportionalcontrol in minimum time (T). However, if the integral action is too quick it will havethe same effect as too much gain and the system will start to oscillate.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





3.3.3 Proportional + Integral + Derivative (PID) Control.

Figure 3-6 Proportional + Integral + Derivative Control

Figure 3-6 shows the effect of adding derivative action to a proportional and integralcontroller. Derivative action (rate) produces a signal which is a function of the rate ofchange of the error signal. This will give a quick start to the output change.Derivative action makes the system settle down at the new set point in a muchquicker time (t). The problem with derivative action is that it is not stable. The quickchanges in output can cause the control element to swing open and closed too fast.This can happen easily when the set point is changed. So, derivative action is only

used if the control loop changes very slowly (e.g. temperature control of a boiler).

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





3.4 THE PNEUMATIC CONTROLLER

The pneumatic controller still has its uses. It is often used in remote places,because it needs no electrical supply. It can also be run on separated gas instead ofan air supply. The most common pneumatic controller is the Foxboro 43 AP (airsupply) or 43 APG (gas supply). This is an independent unit which will indicate andcontrol pressure, vacuum, temperature or flow depending on the sensor fitted andthe scale supplied. Figure 3-7 shows a 43 AP pressure controller.

Figure 3-7 The Foxboro Type 43 AP Pneumatic Controller

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





• The output pressure from the nozzle is amplified by the control relay. Thisamplified pressure produces the output signal through the auto/manual

switch.

• The balancing feedback for the system is fed, through the derivative unit, tothe proportioning (feedback) bellows. The derivative restrictor sets the timebefore the feedback bellows can act. So, the output starts at a maximumbefore the system starts to balance. This activates the quick start for thecontroller.

• The output signal also goes to the reset bellows via the reset (integral) unit.The reset restrictor slows down the filling of the reset bellows but eventuallythe pressure in the reset bellows will cancel the pressure in the feedback

bellows. This will cancel the offset.

• The setting of the proportional band (gain) is done by moving the flappercloser or further from the nozzle. The Foxboro system has a special fittingcalled a striker bar. This allows the operation of the controller to be reversed. An increasing error signal can produce either an increasing output or adecreasing output.

• An auto-manual switch is included. The balance indicator should be in themiddle before the system is changed from manual to automatic. If it is not inthe middle the loop will be "bumped" changing from one output to the other.

• This is a brief description of the operation of the Foxboro 43 AP. You willunderstand the system better after doing practical work in the workshop.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





The combined signal of the output, for a set point change, will look as shown inFigure 3-9.

Figure 3-9 Controller Output Signal with P +I+ D Action

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





3.5 THE ELECTRICAL / ELECTRONIC CONTROLLER'

3.5.1 Introduction

The standard electrical control loop is a series connected system which uses a4-20mA current signal for a 0-100% measurement range. It also uses a 4-20mAcurrent signal to operate the final control element (control valve) which can movefrom fully open to fully closed. This method is being replaced by what are calledSMART SYSTEMS and DIGITAL SYSTEMS. The following notes are given as abrief introduction to the systems in use.

3.5.2 The Standard Electrical Control Loop

Figure 3-10 The 4-20 mA Electrical Control Loop

Figure 3-10 shows a typical electrical single process control loop. The transmitteracts as a variable resistor. The process variable changes the current over the range

4-20 mA. Normally a 250 Ω resistor changes the signal for the controller to a 1.5 Vsignal. This resistor may be placed on a card called a CONDITIONING CARD whichis separate from the controller, or it may be inside the controller itself.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





The controller produces proportional, integral and derivative actions electronicallywhich have the same effects as a pneumatic controller. Reset, rate and proportional

band (gain) controls are variable resistors, which can be adjusted with ascrewdriver.

The output from the controller is also a 4-20 mA series loop. The loop current isconverted by a current to pneumatic converter (I/P). This provides the pneumaticsignal for the control valve.

3.5.3 The Smart Electrical Control Loop

Figure 3-11 The Rosemount Smart Transmitter

Figure 3-11 shows a typical smart transmission loop. The transmission signal is

4-20 mA, as in a standard loop. However, pulsed signals are placed on top of this.The communicator (smart family interface 268) uses these pulses to look into thesystem. It checks the control loop and resets the 4mA (zero setting) and 20mA(span setting).

Note : The communicator can be placed anywhere in the loop but the loop

resistance must be more than 250Ω. This resistance is normallyprovided by the safety barrier. Remember the safety barrier is includedto prevent dangerous voltages and currents from happening if there is afault.

The system shows a Rosemount transmitter but the Foxboro 800 series and the

Honeywell 3000 series work in much the same way. However, each type has itsown communicator.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





It is possible to have a smart output loop with a computer operated control valve.However, these are very specialised and must be learnt on the job.

3.5.4 The Digital Loop.

he latest transmitters (Foxboro 860 series) use only pulsed (digital) signals to sendthe measured -value to the controller. There is no 4- mA loop and the systemoperates using a voltage supply from a special unit in the controller. A simplifieddiagram of the system is shown in Figure 3-12.

Figure 3-12 Digital Control Loop

The hand held communicator can be placed in any position in the loop to check thesystem and perform zero and span checks.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r





3.5.5 Electronic Controller

There are basically three types of electronic controller.

• The analog type (eg. Foxboro, Spec 200)

These provide P and ID control of continuously changing (analog) signals.They uses a standard operational amplifier similar to the ones made in theelectronics workshop.

• Digital type (eg. Foxboro 760 Series)

These provide single loop control using a small computer' (microprocessor).

The settings are changed using a keyboard on the front of the unit.

• Digital type - Workstation Operation

The latest type of controller. Examples of these are listed below.

Honeywell TDC 3000

Foxboro 1 A

Bailey INFI 90

These controllers can operate a number of control loops at a time (around 20). Thedisplay for each loop is shown on a work station screen (similar to the officecomputer). The operator/technician changes the loop variables (eg. set point andPID settings) using a typewriter keyboard.

M o

d u

l e N

o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

3 -

T h e c o n

t r o

l l e r



July 1999- Rev.0

Page 2/29


TABLE OF CONTENTS

Para Page


4.1 INTRODUCTION 4

4.2 VALVE TYPES 4

4.3. THE GATE VALVE 5

4.4 THE GLOBE VALVE 6

4.4.1 The Industrial Globe Valve. 7

4.5 THE BUTTERFLY VALVE 9

4.6 BALL AND PLUG VALVES 10

4.7 THE PINCH VALVE 13

4.8 THE NEEDLE VALVE 15

4.9 THE CHECK VALVE 16

4.10 PRESSURE RELIEF (SAFETY) VALVE 18

4.11 ACTUATORS 19


4.11.2 The Pneumatic Actuator (Diaphragm Type) 19

4.11.3 The Pneumatic Actuator (Piston Type) 21

4.11.4 The Electrical Actuator 22

4.12 VALVE CHARACTERISTICS 24


4.12.2 Flashing and Cavitation 26

4.13 EMERGENCY SHUTDOWN OPERATIONS 28

4.14 CONCLUSION 28

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 3/29




• Describe, with the aid of a sketch, the following valve body types.

Gate

Globe

Butterfly

Pinch

Needle

Ball and Plug

Check Valve

Pressure Relief (Safety) Valve

• Describe, with the aid of a sketch, the following types of actuator.

Hand

Diaphragm

Piston

Electrical

• Explain, with diagrams, the control characteristics of a complete controlvalve assembly.

• Explain, with diagrams, the terms 'FAIL OPEN, 'FAIL CLOSE.

• Explain, with diagrams, the causes and effects of flashing and cavitation.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 4/29


4.1 INTRODUCTION

The aim of this unit is to describe and explain the types of valves and actuatorsused to control the flow of a fluid in a process.

4.2 VALVE TYPES

The valves used on a plant can be grouped into two main types.

Shut Off Valves: Shut off valves can be operated by hand or operatedautomatically using an actuator. Their purpose is either toallow full flow through the valve or shut off the flowcompletely. They must not be used to control the amount of

flow.

Control Valves: Control valves can also be operated by hand. However, theyare normally operated by an actuator automatically. Theirpurpose is to control the amount of fluid passing through thevalve and to act as the correcting element for a control loop.

There are many different valve designs. They can be very simple (e.g. a water tap).They can be very complicated (e.g. low noise valves for the control of high pressuregas). The following notes are given as an introduction to the valve types available.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 5/29


4.3 THE GATE VALVE

The gate valve is the common shut-off valve for a pipeline. It is designed to beeither fully open or fully closed. Any position between the two can cause a lot ofdamage to the valve.

Figure 4-1 The Gate Valve

Figure 4-1 shows the two common forms of gate valves. These valves are handoperated.

Rising Stem: This is a simple device. As. the handle is turned thescrew thread on the stem pulls up or pushes down thedisc gate. The valve is designed for two positions only,

fully open or fully closed.

Non Rising Stem: The handle turns the stem. The stem fits into thesleeve which has an inside thread, As the stem turns,the inside thread causes the sleeve and gate to moveup or down. This type of gate valve is used for higherpressures. The gate is split so that both sides areforced tight against the two seats. This gives a tightshut off.

Note: The rising stem valve is normally turned back a 1/4 of a turn after settingfully open or closed. This stops it from sticking if it is left for long periods

in one position. This must never be done with a non rising stem valve.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 7/29


4.4.1 The Industrial Globe Valve.

Industrial globe valves come in all shapes and sizes. However, they can be split intotwo main groups; the "shaped plug" and the "plug and cage".

THE SHAPED PLUG GLOBE VALVE.

Figure 4-3 Typical Shaped Plug Globe Valves

Figure 4-3 shows the construction of a shaped plug globe valve. The single plugvalve is used for flow control at low pressures. High pressure control is difficult asthe line pressure pushes against the plug. Therefore, extra force must be applied tothe stem to hold the plug in position. The double plug system (see Figure 4-3b)overcomes the problem of line pressure by providing two controlled flow streams.The pressure on the top plug forcing the stem up is balanced by the pressure on the

bottom plug forcing the stem down. So, less force is needed to move the stem andyou have good control at high pressures. The diagram also shows the two types ofvalve body. Figure (a), is direct. As the stem rises the flow increases. Figure (b) isreverse. As the stem rises the flow decreases.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 8/29


THE PLUG AND CAGE GLOBE VALVE

Figure 4-4 The Plug and Cage Globe Valve

Figure 4-4 shows a plug and cage globe valve. The flow through the valve is viaholes cut in the cage. The amount of open hole, and thus the flow, depends on theposition of the plug. The plug is held in position by a force on the stem. Most of theglobe valves used in the oil/gas industry are of the plug and cage type. They arecheaper to manufacture and service, and provide a balanced action with a simplehole through the plug. The pressure at the top of the plug balances the pressure atthe bottom of the plug. The diagram above shows a direct acting body. A reverseacting body is also available but it is very unusual.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 10/29


The discs in butterfly valves can have different shapes. Different shape discs canimprove throttling characteristics and provide a tight shut-off. A popular model is the

Fisher Fishtail. Figure 4-6 shows the shape of a Fishtail butterfly disc. The sectionaldrawing shows how a tight shut-off can be obtained.

Figure 4-6 The Fishtail Disc and Sealing Diagram

4.6 BALL AND PLUG VALVES

Ball and plug valves are 1 /4 turn valves which operate in the same way as abutterfly valve. The only difference between the two is the shape of the part beingrotated in or out of the flow steam. Figure 4-7 shows a typical ball and plug valve.

Figure 4-7 The Ball and Plug Valve

The ball valve is a sphere with a hole drilled in it. The plug valve is a tapered

cylinder with a hole drilled in it. All these valves are designed so that the actuator(handle) puts the hole in line for full flow as shown in the diagram below.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 11/29


These valves are popular as shut-off valves, particularly in air lines and processlines to instruments. They are also used as control valves. There are many differentdesigns.. Two of the common ones used in the oil/gas industry are the Fisher "V"ball and the Masoneilan eccentric plug (eccentric means off-centre). TheMasoneilan eccentric plug valve is shown in Figure 4-8.

ECCENTRIC PLUG

ACTUATOR ROD

Figure 4-8 The Masoneilan Eccentric Plug

The actuator turns the plug a 1/4 turn, from fully closed to fully open. The plug isshaped to provide flow control similar to a globe valve.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 12/29


Ball/plug valves are often used to provide three/four way connections. This is doneby drilling the hole in the ball in different ways. Some examples are given in Figure

4-9.

Figure 4-9 Multiway Valves

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 13/29


4.7 THE PINCH VALVE

The pinch valve is used to control the flow of very corrosive liquids, eg. acids. Theflow passes through a flexible pipe or diaphragm. The pipe must be made ofmaterial which does not corrode easily. The pipe is squeezed or pinched to throttlethe flow. There are two basic types which work in much the same way.

Figure 4-10 Saunders Half Pinch Valve

The SAUNDERS VALVE is a patented device. From the simplified diagram (seeFigure 4-10) it can be seen that the actuator throttles the flow by pressing thediaphragm closer to the weir. The body itself is insulated from the corrosive liquid bya glass or plastic coating. The stem is connected to an actuator (either hand orautomatic control)

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 14/29


Figure 4-11 The Pinch Valve

The PINCH VALVE shown in Figure 4-11 uses a mechanical linkage to squeeze topand bottom together. The flexible sleeve is made of a synthetic rubber. When youturn the hand wheel it throttles the flow to the rate you want. An automatic actuatorcan be fitted to this device if required.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 15/29


4.8 THE NEEDLE VALVE

The needle valve is used to control very low flows (e.g. chemical dosing of pipelinesto stop corrosion). A typical example of a needle valve is shown in Figure 4-12.

The flow is controlled by a needle plug which fits into a small hole in the seat. Thesevalves can have manual or automatic actuators. When it's made from a solid blockof stainless steel it can give very low flow control at very high pressures (e.g.100,000 psi).

Figure 4-12 The Needle Valve

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 16/29


4.9 THE CHECK VALVE

The check valve is a non-return valve. It allows fluid to flow in one direction only inthe same way as a diode allows an electrical current to flow in one direction only.There are two types of check valve; swing check and lift check.

SWING CHECK

This is the method used for large flow rates through big pipe lines. Figure 4-13shows a typical swing check valve.

Figure 4-13 Swing Check Valve.

The swing check valve consists of a disc assembly which is free to rotate on thepivot pin. In the open position the fluid pressure on the disc swings it into theposition shown. This allows full flow through the valve. In the reverse direction thepressure on the disc forces it hard against the valve seat and no flow is possible.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 17/29


LIFT CHECK.

This is the method use for smaller flow rates and pipelines. Figure 4- shows atypical lift check valve.

Figure 4-14 Lift Check Valve

The lift check valve is similar to a globe valve. However, the plug is free to move. Ifthere is no flow the weight of the plug closes the valve. Normal flow lifts the plugand allows the fluid to pass through the valve. If the pressure across the valve isreversed the plug is forced down against the seat and no reverse flow is possible.

Note: A lift check valve does not open to the full pipe diameter like a checkvalve so it is not suitable for high flow rates.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 18/29


4.10 PRESSURE RELIEF (SAFETY) VALVE

Pressure Relief (Safety) Valves are mechanically set valves which open to relieve

pressure when automatic control is lost. There are many different designs for thistype of valve, divided into two basic groups.

a) Liquid pressure relief, normally called "Pressure Relief Valves (PRV)

b) Gas pressure relief, normally called "Pressure Safety Valves" (PSV)

The basic difference is in the speed of operation. PSV's must relieve the pressuremuch faster than PRV's.

Figure 4-15 Pressure Relief Valve.

Figure 4-15 shows a typical pressure relief (safety) valve.

Operation:

1 . Under normal conditions the valve is closed because of the force applied bythe spring.

2. The inlet pressure is applied to the under side of the disc.

3. If the inlet pressure reaches the relief pressure the disc lifts against thespring. The valve opens and the excess pressure is released; in thisexample, to the flare.

4. The device is calibrated using a dead weight tester. The relief pressure isset by using the adjusting bolt to control the force applied by the spring.

Note: The relief valve shown is only an example. Only certified technicians can

calibrate safety relief valves. Each manufacturer holds special certificationcourses for its safety valves. You will do these special courses duringtraining on the job.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 19/29


4.11 ACTUATORS

4.11.1 Introduction

Actuators are the devices which drive the valve stems. There are many differentactuators. They range from the simple handwheel to the latest microprocessorcontrolled electrical/hydraulic actuators. The following notes introduce the commontypes of actuator in general use by operating companies. You will learn aboutspecialised actuators used on a particular site during advanced training.

4.11.2 The Pneumatic Actuator (Diaphragm Type)

Figure 4-16 Air to Close Pneumatic Actuator

Figure 4-16 shows a typical sectional view of an air to close, pneumatic actuator.With a minimum air signal (3 psi or 0.2 bar) applied to the loading pressureconnection, the spring forces the stem to its maximum upwards position. With amaximum air signal (15 psi or 1 bar) the force on the diaphragm compresses thespring and the stem moves down to the closed position. Any signal between the twowill hold the stem at an intermediate position to control the flow.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 20/29


The actuator can be designed to work in the opposite direction, i.e. air to open.Figure 4-17 shows a typical air to open actuator. The air signal input is applied to

the underside of the diaphragm (loading pressure connection).

Figure 4-17 Air to Open Pneumatic Actuator

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 21/29


4.11.3 The Pneumatic Actuator (Piston Type)

Figure 4-18 A piston Pneumatic Actuator

Figure 4-18 shows a typical pneumatic piston actuator. It is used to operate a ball orbutterfly valve. In the position shown the valve is about half way. An increase in thepressure (P1), forces the piston further down and rotates the ball or butterfly. Thiscloses the valve more. The system is balanced by the feed back signal (P 2). P2 isprovided by the Actuator Control Unit (positioner). The operation of pneumaticpositioners will be explained later in the course. If P1 fails the opposite occurs, P2 increases and the valve opens more.

The actuator rotates the V ball through 90°. When the valve is closed the ball stopsthe fluid flow in the same way as an ordinary ball valve. As the valve opens the "V"cut in the ball allows fluid to pass at an increasing rate to the fully open position. So,the "V" ball is an efficient control valve similar to the globe type.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 22/29


4.11.4 The Electrical Actuator

There are two common types of electrical actuator; the solenoid type used inemergency shut down systems and the motor operated type used when loadingtankers from a marine terminal.

THE SOLENOID OPERATED VALVE (SOV)

Figure 4-19 The Solenoid Valve

This on/off valve is used to remotely open or shut a flow line. These valves normallycome in small sizes. (e.g. 2" diameter). It is often used for the control of air supplylines etc. in Emergency Shut-Down (ESD) systems.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 23/29


THE MOTOR OPERATED VALVE (MOV)

Figure 4-20 shows one of the latest types of motor operated valve. The valve iseither open or closed. An electrical signal goes to an electric pump. This drives thehydraulic fluid to open the valve. If the signal stops, the hydraulic pressure falls anda spring returns the valve to the closed position.

Figure 4-20 The Electro Hydraulic Actuator

These valves are used in large diameter pipelines (e.g. 20" diameter). They controlthe flow of petroleum products being loaded onto a tanker, etc.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 24/29


4.12 VALVE CHARACTERISTICS

4.12.1 Introduction

The plug or cage of a valve can have different shapes. The different shapes cancontrol- the flow in different ways. There are three main types of controlcharacteristics; linear, equal percentage, and quick opening.

The graph below shows how these control characteristics change the flow as thevalve is opened.

A quick opening characteristic gives nearly maximum flow for a small % openingdistance of the plug, (plug travel).

A linear characteristic provides the same change of flow for the same change inplug travel (e.g. 50% open, 50% flow; 20% open, 20% flow; etc.)

An equal percentage characteristic means the plug travel provides a constantpercentage change in the flow rate. This is shown on the graph as a flow which getsfaster as the valve opens. At a 20% flow rate a 10% increase means the valveopens to allow the flow rate to increase to 22%. However, a 10% increase in theflow rate at 80% means the valve opens to allow the flow rate to increase to 88%.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 25/29


Which characteristic is used depends on the property being controlled. A fewexamples are given below.

Linear - Liquid level and flow control

Equal Percentage - Pressure control

Quick Opening - Pressure relief valves.

The cages and plugs for the different characteristics are easy to tell apart as thefollowing examples show:

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 26/29


4.12.2 Flashing and Cavitation

Figure 4-21 Pressure Curve through a Valve

Figure 4-21 shows the effect of a valve throttling a flow steam to control the flow.The valve acts like an orifice plate. The pressure will fall across the valve as thevelocity increases through the restriction.

If the pressure of the liquid falls below the bubble point the gases in the liquid underpressure will be released as bubbles. This is called the flashing point. As thesebubbles keep hitting the valve plug and seat they can wear away the metal.

As the fluid leaves the valve the pressure increases again. This makes the bubblesimplode. This is called the cavitation point. The sudden implosion of the bubblescan wear away the metal on the plug, seat and valve body. The two pictures below(see Figure 4-22) are examples of flashing and cavitation damage.

Flashing and cavitation are two problems with valves which control liquid flow.When you service a control valve you must check the plug and cage for signs ofdamage caused by these problems. Report any damage as the valve may need tobe redesigned to stop more damage which could cause a shutdown.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 27/29


Figure 4-22 Flashing and Cavitation Damage

Most manufacturers make special cages to stop flashing and cavitation. Thesecages split the flow into small flow streams. This reduces the possibility of damageand noise as the flow rushes through the valve. Typical examples are shown inFigure 4-23.

Figure 4-23 Anti Cavitation/Noise Cages

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 28/29


4.13 EMERGENCY SHUTDOWN OPERATIONS

Various valve/ actuator assemblies on a plant are made to "fail open" or "fail closed"in an emergency shutdown. The valve and actuator can be made in the followingways to produce the "fail open" or "fail closed" conditions.

FAIL OPEN:

1. Air to close actuator with direct operating valve body

2. Air to close actuator with reverse operating valve body.

FAIL CLOSED:

1 Air to open actuator with direct operating valve body

2. Air to close actuator with reverse operating valve body.

Most plants use direct operating valve bodies. They get "fail open" or "fail closed" byusing air to close or air to open actuators. However, the other combinations aresometimes used.

A piston type actuator can be made either "fail open" or "fail closed" by thepositioner. It is also possible for the positioner to hold the valve at it's last controlposition. That is usually called "fail intermediate".

4.14 CONCLUSION

The previous pages have provide a general introduction to valves and actuators.However, the subject can be very detailed and an engineer/technician can spend allhis working life on valve operations only. A table is added at the end to summarisethe facts you have learned. It gives a summary of the uses of valves.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s



July 1999- Rev.0

Page 29/29


M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

4 -

V a

l v e s

& A c

t u a t

o r s











M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

5 -

P r a c

t i c a

l t a

s k s





TABLE OF CONTENTS

Para Page

PRACTICAL TASK 1 3

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

5 -

P r a c

t i c a

l t a

s k s





PRACTICAL TASK 1

CALIBRATING AN INDUSTRIAL THERMOMETER

INTRODUCTION

Most industrial thermometers cannot be calibrated. All you can do is check that theyare reasonably correct. This is true for mercury in glass and bi-metal stripthermometers.

However, some of the "filled system" types can be calibrated for zero and span. Youcan calibrate for zero by adjusting the pointer. You can calibrate for span byadjusting the Bourdon tube linkage, in the same way as with a pressure gauge.

TEMPERATURE STANDARDS.

The basic standards for all temperature calibration are:

1 ) The ice point; ice melting in distilled water at a standard pressure of 101 325

Pa. This is 0° C or 32° F.

2.) The boiling point of distilled water at a standard pressure of 101 325 Pa.

This is 100°C or 212°F.

Other fixed points for temperatures outside this range are internationally agreed.This is called the International Practical Temperature Scale (IPTS). A few examplesof these points are given below:

Boiling point of oxygen - 182.962 ° C

The freezing point of mercury - 38.862 ° C

The freezing point of zinc - 419.58°C

The freezing point of silver - 961.93 °C

The freezing point of gold - 1064.43°C

You will probably never see any calibrations carried out using these standards. Thecalibration equipment in the instrument workshop is calibrated when it ismanufactured. It is calibrated against the above standards and given a calibrationcertificate which shows its accuracy. When you get it from the manufacturer yourequipment should be correct. A good instrument workshop sends its calibrationequipment for re-calibration every year. Then a new calibration certificate is given.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

5 -

P r a c

t i c a

l t a

s k s





The most common industrial standard thermometer is the platinum PT 100 Ω. This

should be accurate to 0.1° C over the range 15 to 1000° C. This thermometer isfitted into a temperature bath (usually sand filled or solid block). The electrical

heater for the temperature bath is controlled by the PT 100 Ω. The temperature ofthe bath is given on a digital read out. An example of a workshop temperaturecalibration bath is shown in Figure PT-1. The AMETEK dry block calibrator has a

range of -40 to 1 23°C and an accuracy of ± 0.5°C.

Figure PT-1 Arnetek Dry Block Calibrator

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

5 -

P r a c

t i c a

l t a

s k s






The CDC does not have a modern temperature calibration bath. The following

calibration is done using a "sand filled" temperature bath which does not keep sucha steady temperature. The standard temperature is set using a semi-standardmercury in glass thermometer. Remember to use the immersion line for correct

calibration. An ice/water mixture is used as the standard 0°C A layout of thecalibration procedure is shown in Figure PT-2.

Figure PT-2 Basic.Thermometer Calibration

CALIBRATION STEPS

1) Place the thermometer which you are testing in the ice/water mixture. Itshould read zero on the scale. If the thermometer is the filledsystem/Bourdon tube type, adjust the pointer to read zero.

2) Place the thermometer which you are testing in the temperature bath andadjust the set temperature so that you get the maximum indication on thethermometer dial. If the thermometer is of the filled system/Bourdon tubetype, adjust the linkage to the maximum indication point.

3) Non adjustable thermometers are OK if they are within ± 4°F or ± 2°C

4) The filled system types can, with care, be set to an accuracy of about ± 1° C.

Note: The above calibration procedure is the same using a moderntemperature bath, but the ice is not needed. Also the quick response ofthe modern bath allows you to plot a graph to show linearity. The CDCbath needs an air supply. The air flows through the sand so that thetemperature is the same in all parts of the sand bath.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

5 -

P r a c

t i c a

l t a

s k s





Figure PT-5 shows a block layout for the calibration of a T/C transmitter. The T/Ccalibrator simulates the T/C temperature by sending a mV signal which correspondsto the T/C type J, K, N etc.). The DVM is usually connected across the test position.

The zero and span are adjusted to give a 4-20mA output signal corresponding tothe T/C sensor range (eg. 100-400°C).

Note : Sometimes it is better to add your own standard resistor in series withthe output. The DVM is then placed across this to measure the 4-20mA.

A typical standard resistor is of the wire wound type (eg. 10Ω ± 0.1 %).This produces a 40mV to 200mV signal.

• When the transmitter is of the RTD type

Figure PT-6 Calibration of RTID Temperature Transmitter

Figure PT-6 shows the block layout for the calibration of an RTD temperaturetransmitter. The input RTD resistance value for the temperature comes from adecade box (standard variable resistor). The output 4-20mA is measured by usingeither the test position or a standard resistor.

The zero is adjusted to give 4mA for the minimum temperature set by the decadebox. The span is -adjusted to give 20mA for the maximum temperature set by the

decade box.

Note : Modern calibrators produce a resistance output so a decade box isnot required. The calibrator is connected to the transmitter. In thiscase a three wire system is used. The calibrator is then programmedto give the required RTD resistance values.

M o

d u

l e

N o .

2 :

I n s

t r u m e n

t a t i o n

2

U n

i t N o .

5 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 3

INSTRUMENTATION 3






UNIT 1 CONVERTERS AND POSITIONERS

UNIT 2 RECORDERS

UNIT 3 INDICATORS AND COMBINED UNITS

UNIT 4 HAZARDOUS AREAS AND INTRINSIC SAFETY

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s







• Explain the need for I/P and P/l converters.

• Explain the operation of a typical I/P converter e.g. Foxboro.

• Explain the purpose of a positioner.

• Explain the operation of a typical valve positioner e.g. Fisher.

• Explain the operation of a modern combined electrical/pneumaticconverter/positioner, e.g. Fisher, Rosemount.

• Explain the operation of typical pneumatic signal to electrical signalconverters, e.g. Rosemount, Foxboro.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





1.1 INTRODUCTION

The aim of this unit is to explain:

• The operation and use of equipment which converts electrical signals topneumatic signals (I/P)

• The valve positioner and its uses

• The combined valve positioner and I/P.

• The pneumatic signal to electrical signal converter (P

1.2 THE ELECTRICAL TO PNEUMATIC SIGNAL CONVERTER (11/P)

1.2.1 Introduction

The electrical to pneumatic signal converter (I/P) is an important piece of pneumaticequipment. This is because, even with modern digital transmission systems, mostcontrol is done with pneumatically operated valves. The 1/P is therefore an essentialitem in any electrical / lelectronic control system.

The basic mode of operation is the "electric motor principle". A current passed

through a conductor in a magnetic field will make the conductor move. The mostcommon type of I/P which is used a lot in the field is the Foxboro (E69F).

1.2.2 The Foxboro I/P Converter (E69F)

Figure 1-1 The Foxboro I/P Converter M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





Figure 1-1 shows a schematic diagram of the Foxboro I/P converter. The coil,permanent magnet and coil flexure are mounted inside a can made of magnetic

material, e.g. soft iron. The can is not shown in the diagram to make it easier tosee. The can makes the magnetic field produced by the permanent magnet run atright angles to the coil. This makes a system similar to a moving coil meter, asshown in the sketch below.

Basic Operation:

An increase in the input current through the coil makes the coil rotate. This movesthe flapper towards the nozzle. The back pressure is increased. The change is

amplified by the relay and applied to the feedback bellows. This makes the nozzlemove away from the flapper until it reaches a new balance position.

The system is arranged so that when the coil current reaches the upper range value(e.g. 20mA), the pneumatic output signal reaches its own upper range value (e.g. 1bar). The signal can be adjusted a little by moving the nozzle radially at an angle tothe axis of the coil.

Note:- The coil flexure acts as the restoring spring. With minimum current throughthe coil (e.g. 4mA), the flexure returns the coil to its - starting position andsets a minimum output pressure (e.g. 0.2 bar).

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





Figure 1-3 shows a Fisher valve positioner for piston actuators. Figure 1-3(a) showsa diagram of the layout of the positioner. Figure 1-3(b) shows the positioner fitted to

the piston actuator.

OPERATION

1) The input signal is applied to a bellows. This bellows applies a force to adouble flapper assembly which moves using the flexure as a pivot.

2) If the input signal increases, flapper "B", moves away from relay "B" andflapper 'W' moves nearer to relay "A". The signal pressure from relay 'W'increases and the signal pressure from relay W' decreases.

3) The higher pressure on the top of the piston (relay A) moves the piston

down. Therefore the stem moves down to close the valve.

4) The range spring provides the feedback to the system so that the valve isrepositioned at the new input controlled position.

5) If t-he input signal decreases the opposite action occurs. The piston movesup to open she valve at the new input controlled position.

6) The bias spring is adjusted to give the fully open position. This is the "Zero"adjustment where a 3 psi (0.2 bar) input sets the valve fully open.

7) The "span" is set by the range spring. This is selected to give a fully closed

valve with a 5 psi (1.0 Bar) input signal.

8) The positioner is easily changed to provide reverse action (input signal 3 psifully closed) by changing the position of the input signal bellows (as shown).

Note:

The above operation assumes the valve body is direct acting (stem moving downcloses the valve).

If the valve requires a reverse action, place the input bellows on the opposite side ofthe lever as shown.

There are many different types of this positioner/actuator. The type used dependson the length of stroke of the valve and the operating pressures required. Themanual must be consulted if the actuator/positioner is not of the standard typedescribed.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





1.5 THE COMBINED UP AND POSITIONER

1.5.1 The Fisher Electro-Pneumatic Positioner

Schematic diagram of positioner

Figure 1-4 The "Fisher" Electro-Pneumatic Valve Positioner

Figure 1-4 The “Fisher” Electro-Pneumatic Valve Positioner

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





Figure 1-4 shows the Fisher combination UP and positioner.

OPERATION

• The electric current is changed to pneumatic pressure using a 4 coil systemand a magnetic armature.

• The current passing through the coils produces a magnetic field as shown.The armature is pulled up by the positive connection coils and pushed downby the negative connection coils.

• The armature acts as a flapper against the nozzle. A high signal currentpushes the flapper nearer to the nozzle and produces a high output signal.

• The relay amplifies the nozzle output and applies it to the diaphragm tomove the valve stem.

• Feedback is provided by the lever system.

The solid arrows show the movement as the diaphragm pressure increases. Thefeedback spring pulls the armature down. The supply current pulls it up. These twoopposing forces stabilise the system as the signal current gets higher. If the signalcurrent fails the action is reversed. This is shown by the dotted arrows.

Note:

1) The current to pneumatic conversion unit (torque motor) must never betaken to pieces. If you do this, you cannot set it up again, as the magneticcircuit is ruined.

2) The setting up of this unit is complicated and will be done in the workshopusing the manuals.

3) The torsion rod acts like the controlling spring in a moving coil meter. Whenthe signal current is removed the torsion rod puts the armature back to itshorizontal position.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





1.6 PRESSURE TO CURRENT CONVERTERS (P/I

1.6.1 Introduction

The pressure to current converter (P/1) is the opposite of the current to pressureconverter (I/P). It changes an input pressure signal (e.g. 3-15 psi) to a standardelectrical signal (e.g. 4-2OmA). The two examples given in the notes are theRosemount type 11 35F and the Foxboro type 892.

1.6.2 Rosemount Type 1135F P/I Converter

Figure 1-6 Rosemount 1135F P/I

Figure 1-6 shows a Rosemount 1135F P/I fitted to a pipe for use in the field.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





OPERATION

The 1135F P/I uses a capacitive cell (the same type as the Rosemount electricalpressure transmitter). The3-15 psi or 0.2-1 bar pneumatic signal is applied to oneside of the cell. Atmospheric pressure is applied to the other side of the cell. Themovement of the sensing diaphragm (maximum 0.10 mm) depends on thedifferential pressure across it. The difference in capacitance (C1-C2), as the sensingdiaphragm moves, is measured by the electronics to provide the 4-20mA signal.

There is only one adjustment in the electronics. The zero adjustment. This sets thedevice to give 4mA output for a 3 psi or 0.2 bar input. The span of the device is setin the factory to meet customer requirements.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





1.6.3 The Foxboro 7010A P/1 Converter

Figure 1-7 shows the basic principle of the device.

DUAL UNIT P/1 CARD 7010A

Figure 1-7 Foxboro P/1 Converter 7010A

Foxboro produce a dual pneumatic to current converter for mounting in a rackinstead of field mounting. The pneumatic signals are transmitted to the control roomwhere they can be converted to an electrical signal in a safe area. The diagramabove shows the Foxboro 7010A converter together with a rack mounted 7020Anest of these converters.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





This is an analog system which uses operational amplifiers. A simplified diagram ofthe electronics is shown below.

T1

OPERATION

Component “A” is a strain gauge bridge. R1 and D2 provide a constant referenceVoltage for the bridge. The supply to the unit is from an external 24V D.C supply.operational amplifier O1 detects the changes in resistance (voltage) across thebridge and the pressure changes. Operational amplifier O2 produces an outputdepending on the difference between O1 output and the reference voltage. O2 output controls the base voltage and thus the conduction of T1. T1 is a seriestransistor which varies the 4-20mA signal around the loop. D1 is added to stop anyreverse current flow if the power supply is wrongly connected. The span adjustmentadjusts the gain of O1 and the zero adjustment adjusts the reference level for O2.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





CALIBRATION

The calibration of the equipment is simple. The following section is a copy of theprocedure taken from the Foxboro manual. The power supply voltage requireddepends on the resistance of the output load, (e.g. controller input). This is the

receiver on the diagram. This is 24V dc with a 500Ω resistor put in place of thereceiver.

Equipment Setup

Procedure

1) Set up the equipment as shown.

2) Adjust the air supply so that the test gauge reads 3 psi or 0.2 bar.

3) Adjust the zero screw (Channel 1) so that the digital voltmeter (DVM) outputis 100 mV.

4) Adjust the air supply so that the test gauge reads 1 5 psi or 1.0 bar

5) Adjust the zero screw (Channel 1) so that the digital voltmeter (DVM) outputis 500mV.

6) Repeat steps 2 through 5 until you get the desired output.

7) Repeat steps 1 through 6 for Channel 2.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s





Output Load Resistance

To determine the converter's output load resistance, add the input resistance ofeach component in the series loop which is connected to the converter output. The

total loop resistance must not exceed 1000 Ω. As an example, if the resistance is

500 Ω, as shown in the following graph, the supply voltage must be 24 V minimum.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

1 -

C o n v e r t e r s

& P o s

i t i o n e

r s







UNIT 2 RECORDERS



M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 THE PNEUMATIC RECORDER 4


2.2.2 The Foxboro Series 120 Consotrol Recorder 5

2.2.3 Circular Chart Recorder 8

2.3 ELECTRICAL/ELECTRONIC ANALOG RECORDERS 9

2.4 MODERN MICRO-PROCESSOR BASED RECORDER 11


2.4.2 The Foxboro 740 Recorder 11

2.4.3 Conclusion 14

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





2.1 INTRODUCTION

The aim of this unit is to explain the principles of pneumatic, electrical/electronic andmicroprocessor based recorders. These are devices which produce a record of aprocess variable using an ink pen which draws a line on a chart. The chart is rotatedby a motor to give a continuous record over a period of, for example, 24 hours.

2.2 THE PNEUMATIC RECORDER

2.2.1 Introduction

The pneumatically operated recorder is still used today, particularly in remote

locations. It does not use electricity so it does not need any special intrinsic safetymeasures when it is used in hazardous areas. Examples of typical pneumaticrecorders are shown below manufactured by Foxboro. They are the series 120Consotrol recorder and the series 40 circular chart recorder; both made by Foxboro.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





2.2.2 The Foxboro Series 120 Consotrol Recorder

Foxboro produces a range of pneumatic instruments called "Consotrol". TheFoxboro series 120 Consotrol recorder is one of the most common pneumaticrecorders. It is still manufactured and you can get spares for it. You may see othertypes of pneumatic recorders on older sites but they will work in much the same wayas the Foxboro. If you come across a different recorder you should consult themanual before working on it. Figure 2-1 shows the front and top views of theFoxboro 120 pneumatic recorder.

TOP VIEW 4 PEN RECORDER (COVER REMOVED)

Figure 2-1 Foxboro 120 Pneumatic Consotrol Recorder

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





The pens are operated by a bellows and pivot assembly. A sketch of the assemblyis shown in Figure 2-2.

Figure 2-2 Pen Driving Mechanism (Foxboro)

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





Operation

1. The incoming pneumatic signal is applied to a bellows unit which works bycompression against the range spring.

2. As the input signal increases the pen is rotated across the scale. The scaleindicates from 0 to 100% for an input signal of 0.2 to 1 bar (3 to 15 psi).

3. The rotating mechanism has span and zero adjustment screws (as shown)

4. The driving rod from the bellows to the rotating mechanism has a linearityadjustment. This can adjust the linearity of the pen travel from 0-100%.

5. The recorder can drive a maximum of 4 pens.

6. The ink of the pens is supplied from bottles which are refillable. The coloursavailable are red, green, blue and violet.

The chart is driven round by a motor (either electric or pneumatic) at a standard rateof 19 mm per hour. There is enough paper on a roll or flip chart to record around 30days of continuous operation. The calibration and servicing of this recorder will bedone in the workshop during practical tasks. The manual must be used.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





2.3 ELECTRICAL/ELECTRONIC ANALOG RECORDERS

One of the few electrical/electronic analog recorders still available is the Foxboro E

20S recorder. This recorder is a modification of the Spec 200 recorder which youcan practice on in the workshop. This recorder can operate with roll or flip typecharts. The inking system is the same as the pneumatic 120 series but you can getfibre tip disposable pens if required. Figure 2-4 shows the front view of a single penrecorder with a flip chart fitted.

Figure 2-4 Foxboro Type E 20S with Flip Chart

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





Figure 2-5 Foxboro E 20S Pen Assembly (top cover removed).

Figure 2-5 shows ,the pen drive mechanism for a Foxboro E 20S recorder.

Operation:

1 The incoming 4-20mA signal is applied to the pen drive unit. This unit is fullysealed. You can not repair faulty units; you must change the whole unit.

2. The pens are driven from the arbor assembly which is connected to the driveassembly by a link as shown.

3. The arbor assembly contains the zero and span adjustments for setting thepen travel, as shown.

4. The diagram shows a three pen unit. The pen drive units are underneath the

plate holding the arbor and pen stop assembly. A screw type connectionholds the lever assembly on to the shaft of the drive unit.

5. A pen stop mechanism is added to prevent the pen from running off thechart at either end. (0%, 100%). These stops should not be used to set upzero and span.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





2.4 MODERN MICRO-PROCESSOR BASED RECORDER

2.4.1 Introduction

The latest recorders (either roll, flip or circular chart types) use a microprocessor to

give multipurpose recording. The µP is programmed (configured) to set the alarmlevels, engineering units, chart speeds etc. Normally the operator can use akeyboard to get exact indicated readings, totals etc. These are shown on a digitalreadout at the top of the chart. The Foxboro type 740R series is given as anexample of this type of recorder. The following notes give an overview of how itworks. Remember that you must use the manual when servicing this type ofrecorder. The manual will tell you exactly how the device should be configured andoperated. The operator cannot change the programme. The instrument technicianhas a secret password, so that only a technician can change the configuration of

the recorder (usually under instructions from an engineer).

2.4.2 The Foxboro 740 Recorder

Figure 2-6 shows the outside of the Foxboro 740 recorder. Note that the operatorcan use the keyboard to take process readings from the digital readout. He doesnot need to open the instrument or disturb the recordings on the charts.

Figure 2-6 Foxboro Type 740R P Recorder

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





Figure 2-7 (a) Foxboro 740 Recorder (front door removed)

Figure 2-7 (a) shows the recorder with the door removed. Note the addition of a pen

letter. This ensures that the pens make no mess on the chart when it Is changed. ' Also, if the pen is not in use it can be lifted out of the way so there are no uselesslines on the charts.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





Figure 2-7 (b) Foxboro 740 Electronics (platen open)

Figure 2-7 (b) shows the electronics of the recorder., These are under the platen(the name of the plate which holds the pens, chart and chart drive). Note that allconnections and changes to the electronics can be done from the front of therecorder. There is no need to remove the instrument from its field position or controlroom panel mounting.

The electronics cards for the recorder can be selected to record and/or display thefollowing.

Temperature T/C Types B, C, E, J, K, L, N, R, S, and T

RTD 100Ω Platinum, 10Ω Copper, 120Ω Nickel

Signals for pressure, flow rate, level etc. in the following forms:

mA dc 4 to 20mA

mV dc -80 to + 400 mV dc

V dc 0- 100V dc

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s





The electronics provides

a) Cold junction compensation

b) RTD operating currents

c) Mathematical operations on the signals:

Square root, X3/2

, X5/2

and Logx 10.

Instructions about how to fit these cards are given in the manual. The manual also

tells you how to program the µP to provide the correct display and chart recording

values (e.g. °C, bar, litres per minute etc.)

The ink systems today do not use bottles and capillaries as seen in the workshop.

They use disposable felt-tip pens which are easy to change. A Foxboro type, whichis much the same as other manufacturers, is shown in Figure 2-8.

Figure 2-8 Modern Ink Pen Fitting

2.4.3 Conclusion

The Foxboro 720 recorder is typical of any µP based recorder. Most manufacturerssupply these devices in either roll, flip or circular chart form. Each hasinterchangeable electronic cards to measure, display, and record most of theprocess variables. A keyboard is provided to configure the system. The Foxboromanual is typical. It is large and contains all the information required to set up therecorder and programme it.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

2 -

R e c o r d

e r s







UNIT 2 RECORDERS



M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 THE PNEUMATIC SIGNAL INDICATOR 4


3.2.2 The Foxboro 110 Indicator 4

3.3 THE ELECTRONIC INDICATOR 7


3.3.2 The Foxboro 7601 Micro Indicator 7

3.3.3 The Bailey 531T5100 Indicator 9

3.3.4 Rosemount 580D Digital Process Indicator 10

3.4 COMBINATION UNITS 11


3.4.2 The Foxboro 130 Pneumatic Controller 11

3.4.3 The Foxboro 760 Series Indicator/Controller 13

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s







• Use a given diagram to describe the operation of a pneumatic indicator.

• Use a given diagram to describe the operation- of an electrical/electronicindicator.

• Use a given diagram to describe the operation of a typical combined unit,(electrical/electronic and pneumatic) e.g. :

recorder/indicator

indicator/controller

indicator/controller/recorder.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





3.1 INTRODUCTION

The aim of the unit is to explain the use and operation of a control room indicator.The indicator is not often used as a separate unit on its own. Therefore, someexamples of recorder/indicators, indicator/controllers and indicator/controller/recorders are explained to show the more common combined controlroom unit.

3.2 THE PNEUMATIC SIGNAL INDICATOR

3.2.1 Introduction

The pneumatic indicator is now obsolete. It is only seen on old installations or onproduction facilities at remote locations with no electrical supply.

About the only manufacturer still supplying this device is Foxboro. They supply thetype 110 Consotrol pneumatic indicator.

3.2.2 The Foxboro 110 Indicator

Figure 3-1 Foxboro 110 Consotrol Pneumatic Indicator

Figure 3-1 shows the front view of a Foxboro 110 pneumatic indicator which

displays two process variables. (There are indicators which display a maximum ofthree process variables). The scales are made to fit customers' requirements.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





Figure 3-2 below shows an enlarged view of the receiver and pointer drive assemblyfor a 3 variable indicator.

Figure 3-2 Indicator Assembly

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





OPERATION:

The pneumatic signal from the transmitter (3-15 psi or 0.2-1 bar) is applied to thebellows unit (expansion type). The expanding bellows moves the moving plate. Thismoves the pointer across the scale by way of a link adjustment and the pointer driveunit. The amount of pointer movement depends on the input signal.

The customer decides what variable must be measured, e.g. temperature,pressure, flow, etc. The receiver is calibrated using the span and zero adjustmentsas shown. A damping adjustment is added. This stops a pulsating signal frommaking the pointer difficult to read. The calibration of this type of indicator will bedone in the workshop using the manual.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





3.3 THE ELECTRONIC INDICATOR

3.3.1 Introduction

The following notes are given to show three examples of the many kinds ofelectronic indicators available in the market.

3.3.2 The Foxboro 7601 Micro Indicator

Figure 3-3 Foxboro 7601 Micro Indicator

Figure 3-3 shows the front of a Foxboro 7601 micro indicator. This is typical of the

modern µP based indicators. The keypad is used to programme (configure) theindicator to the measurements and alarm settings required. The two measurementbar graphs are calibrated from 0-100%. The actual value is indicated by the numberof LEDs which light up on the bar graph.

The alphanumeric display at the top shows the actual value of input measurementin words and numbers. The operator can use the keyboard to select which value is

displayed.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





The operator can only use the keyboard if he is allowed to change the settings. Ifyou work on this type of indicator you must use the manual both for operating and

reconfiguring. The alarm indicator will flash if the alarm limits are reached. You canfind the alarm readings and settings using the keyboard. However, you must usethe manual to do this. The following input signals can be applied to the indicator.

1) 4-20mA

2) 1-5V

3) RTD in various ranges

The actual units of measurement for the input signal (e.g. level, pressure,temperature) are configured using the input keyboard and the manual.

The manual tells you how to calibrate the indicator. Remember this instrument isaccurate to ± 0.2%. Therefore, the calibration equipment must be accurate to ± 0.1%.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





3.3.3 The Bailey 531T5100 Indicator

Figure 3-4 Bailey 531T5100 Indicator

The Bailey 531T5100 will indicate 4 process variables at one time using what iscalled a "dot matrix" display. On this display the LEDs are points, not bars. Althoughpoints are more difficult to produce, they are clearer and easier to read. Like theFoxboro, the indicator will show a % indication on a bar and the actual value in theunits required on the alphanumeric display (gallons in the diagram). The operatorpresses the buttons on the side to show the different process variables on thealphanumeric display.

The indicator is configured using a special Bailey communicator. This can beplugged into the slot at the front. The inputs can be either 420mA or 1-5V. They canbe transferred directly to an output connection so that they can be used by otherunits (e.g. recorder).

Alarms can be set into the indicator. The outputs can be changed into serial dataform using a RS 232C data port. Another advantage is that the indicator can providea 24-26V dc output so it can drive a transmitter if required.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





3.3.4 Rosemount 580D Digital Process Indicator

Figure 3-5 Rosemount 580D Digital Process Indicator

Figure 3-5 shows a Rosemount 580D digital process indicator. This is a typicalexample of this type of indicator.

The input is the standard 4-20mA. The µLP inside the unit converts this signal to a 4digit display. The range and units are programmed by the push buttons on the front.The example shows gallons per minute but most units can be displayed (e.g.pressure (psi, bar), level (meters, feet)). It has an accuracy of 0.02% of reading ± 1count. Like the Bailey indicator, this unit can be provided with an internal 24dcpower supply to drive a transmitter if required. Another model of this indicator, the

580T, can measure temperature. The 580T will indicate both 100Ω RTDs and mosttypes of thermocouple.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





3.4 COMBINATION UNITS

3.4.1 Introduction

Most manufacturers provide both pneumatic and electronic panel mountedinstruments. These instruments have a combination of functions; for exampleindicator/controller, indicator/recorder and indicator/controller/recorder. The twoexamples below are given to show the basics of these instruments. Both will bedemonstrated in the workshop.

3.4.2 The Foxboro 130 Pneumatic Controller

This unit is part of the consotrol pneumatic range. It combines a PID controller withan indicator. A circular chart recorder can also be added as an optional extra.

Figure 3-6 Foxboro 130 Pneumatic Indicator/Controller/Recorder

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





Figure 3-6 shows the Foxboro combined pneumatic indicator/controller/recorder. Itconsists of the following parts.

1) A process variable indicator which is operated by a receiver bellows andlinkage in the same way as the 110 indicator.

2) A set point indicator and manual adjustment knob.

3) A set of derivative, proportional and reset units. These are adjusted with ascrew driver, positioned as shown.

4) A circular chart recorder (optional extra). The pen unit is driven from theindicator linkage.

5) A manual control unit. This contains a transfer switch (automatic/manual).There is a wheel to adjust the output signal on manual. An output pointerand scale show the output signal as a percentage of the set range.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





3.4.3 The Foxboro 760 Series Indicator/Controller

Figure 3-7 Foxboro 760 Series Indicator/Controller

Figure 3-7 shows the overall view of a Foxboro 760 series indicator/controller.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





The front uses the same type of display as the indicator 760. It is configured as shown inFigure 3-8.

Figure 3-8 Face Plate 760 Indicator/Controller

The following points should be noted.

1) The set point is indicated by a single LED bar on the left hand side.

2) The center scale indicates the measure value.

3) The right hand scale indicates the output signal.

4) The keypad is used to programme (configure) the controller and indicator. Itcan be programmed to give a measured value (scale and unit), PID settings,etc.

5) The status light shows which column value is displayed on the alphanumericdisplay.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





The function of each key on the keypad is as shown in Figure 3-9.

Figure 3-9 Foxboro 760 Keypad

W/P LOCAL/REMOTE INDICATION

W Indication at DCS Workstation VDU

P Indication on front Panel

R/L LOCAL / REMOTE SET POINT

L Local setting by key pad

R Set point from Remote position e.g. from a workstation.

A/M Auto - Manual switch

In NORMAL OPERATION these arrows are used toor change the set point or the output if in manual operation.

In READ or SET mode these arrows are used to

programme the µP.

TAG This is used to change mode from NORMAL OPERATIONto READ or SET mode and back again.

ACK In NORMAL OPERATION this is used to ACKnowledge analarm.

In READ or SET mode this is used to enter changes inthe measured value.

SEL In NORMAL OPERATION this is used to SELect the bargraph status light.

In READ or SET mode this changes the displaying steps

to show what programme has been placed in the µP.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s





760 Inputs

1) 4 analog 4-20mA signals.

2) There are two frequency inputs from 1 to 9 999 Hz. These are used toaccept different signals from, for example, a turbine flow meter.

3) A single 3 wire RTD input.

4) 2 switched contact inputs.

760 Outputs

There are 2 analog outputs; one for a 4 to 20 mA loop and one for a 1-5V dc loop.

There are 2 digital switched outputs.

Note

1. The inputs to the 760, may require the addition of a 250Ω ± 0. 1 % resistorin series with the standard 4-20mA loop current input. This changes the4-20mA signal to a 1-5 V signal for the controller electronics.

2. The 760 can also provide an internal supply (25V dc) to power twotransmitter loops

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

3 -

I n d i c a

t o r s

& C o m

b i n e

d U

n i t s



July 1999- Rev.0

Page 1/21




UNIT 2 RECORDERS



M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -

H a z a r d o u s a r e a s

& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 2/21


TABLE OF CONTENTS

Para Page


4.1 INTRODUCTION 4

4.2 HAZARDOUS AREAS 4

4.3 EXAMPLES OF HAZARDOUS AREAS 5

4.4 HAZARDOUS AREA EQUIPMENT 7

4.4.1 Coding 7

4.4.2 Temperature Rating 7

4.4.3 Gas Grouping 8

4.5 EXAMPLES OF INTRINSIC SAFETY CODING 9

4.6 INTRINSIC SAFETY 12

4.7 THE SAFETY BARRIER 14

4.7.1 One Way Barrier 14

4.7.2 Two Way Barrier 15

4.7.3 References 17

4.8 MODERN TRENDS IN INTRINSIC SAFETY 18

4.9 PRACTICAL POINTS ON HAZARDOUS AREA EQUIPMENT 19

4.9.1 Testing a Barrier 19

4.9.2 Flameproof Equipment 20

4.9.3 Basic Rules 21

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 3/21



The student will be able

• Define what is meant by Zone 0, Zone 1 and Zone 2 hazardous areas.

• Explain the coding of equipment used in hazardous areas.

• Sketch a one way barrier

• Sketch a two way barrier

• Explain how to check a barrier.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 4/21


4.1 INTRODUCTION

The aim of this unit is to explain the system of coding for hazardous areas. It alsoexplains how safety barriers work.

4.2 HAZARDOUS AREAS

A hazardous area is "an area where flammable gases, vapours and mists, andignitable dust, fibres and flyings are present in a mixture with air and could beignited by a spark of energy". Hazardous areas are found in many manufacturingprocesses (e.g. mines, grain silos, gas platforms, refineries etc.). Special electricalsafety systems must be used to ensure that accidents are prevented.

There are many regulations about electrical safety in hazardous areas.Unfortunately they are not the same from country to country. However, in generalthe regulations can be divided into two main groups. The European group uses theInternational Electrotechnical Commission (IEC) code of practice (IEC 79-14). Theother group uses the USA code of practice (ANSI/ISA RP 12.6). The followingdiagrams and tables are designed to show the differences between the two groups.The table below gives the definitions of hazardous areas for both groups.

I.E.C U.S.A

ZONE 0 CLASS 1 DIVISION 1

An explosive gas atmosphere ispresent continuously, or is present forlong periods.

ZONE 1

An explosive gas atmosphere is likelyto occur in normal operation.

Hazardous concentrations offlammable gases or vapours orcombustible dusts in suspensioncontinuously, intermittently orperiodically present under normaloperating conditions.

ZONE 2

An explosive gas atmosphere is notlikely to occur in normal operation and,if it does occur, it will exist for a shortperiod only

CLASS 1 DIVISION 2

Volatile flammable liquids orflammable gases present, butnormally confined within closedcontainers or systems from whichthey can escape only under abnormaloperating or fault conditions.Combustible dusts not normally insuspension nor likely to be thrown intosuspension.

.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 5/21


4.3 EXAMPLES OF HAZARDOUS AREAS

Figure 4-1 shows, as an example, a product tank containing flammable liquid. The

zone system has been applied to the product tank. The tank is surrounded by a wall(bund). The area between the tank and the bund must be large enough to containall the liquid from a full tank in case the tank leaks.

Figure 4-1 Hazardous Areas Zones

The size of each zone depends on the actual construction of the site. Hazardous

area maps of the plant are normally made so that the people concerned, (e.g.electrical and instrument staff) can make sure that the right kind of equipment isinstalled in the hazardous zone. A typical hazardous area plot for an installation isshown on the next page (see Figure 4-2).

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 6/21


ZONE 1

ZONE 2

Figure 4-2 Typical Hazardous Area Plot

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 7/21


4.4 HAZARDOUS AREA EQUIPMENT

4.4.1 Coding

Electrical and instrument equipment fitted in hazardous areas is tested and given acode to show the area where it can be used. A table of the equipment codes isgiven below:

4.4.2 Temperature Rating

The equipment in hazardous areas will also indicate the maximum surfacetemperature it may rise to, in an ambient temperature of 40 0 C. The code is asfollows:Note:- Equipment with a lower maximum surface temperature is safer than

equipment with a higher temperature.

TEMPERATURE CLASS MAX.SURFACE TEMPERATURE 0 C

T1 450

T2 300

T3 200

T4 135

T5 100

T6 85

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 8/21


4.4.3 Gas Grouping

Finally the equipment will indicate in what gas atmosphere it can safely be used.

There are four main groups. An example gas is given.

Note: In the IEC system, group H C is the safest equipment and in the USA

system, group A is the safest group.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 9/21


4.5 EXAMPLES OF INTRINSIC SAFETY CODING

Figure 4-3 MTL Shunt Zener Diode Safety Barrier

Figure 4-3 shows an MTL safety barrier as an example of equipment coding for ahazardous area. - Most international companies code for both IEC and USAstandards as follows:

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 10/21


Figure 4-4 shows another example of a hazardous area coding; an electrical junction box.

Note:

BASEEFA - British Approvals Service for Electrical Equipment in Flammable Atmosphere.

CENELEX - Committee European De Normalisation Electrotechnique.

Figure 4-4 Electrical Junction Box

Field Device Labelling

Field device labelling (e.g. transmitter, I/P converters, switches, etc.) for hazardousareas depends on the manufacturer. Some will put on a label if requested. Someput on only the national code (e.g. Foxboro : factory mutual). Some put the codeinside the serial number (e.g. Rosemount). Therefore, to find out if the device fitsthe area it is placed in, the manual must be consulted.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 11/21


INGRESS PROTECTION SYSTEM

GLOSSARY:

Ingress protection system = A system which prevents unwantedsubstances from getting in to equipment.

Immersion = Going under water for a short time

Submersion = Saying under water all the time.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 12/21


4.6 INTRINSIC SAFETY

Intrinsic safety means safety devices built in to the equipment. It is very unlikely that

ordinary electrical equipment, e.g. Motors, fans, lights etc. will ever be placed in azone 0 hazardous area. So, intrinsic safety systems are only used withinstrumentation. There are two classes of intrinsically safe equipment under theEuropean system; Ex ia and Ex ib.

The definition of Ex ia is given below. It is almost the same as the USA definition ofintrinsically safe equipment.

Ex ia Electrical apparatus (equipment) of category "ia" shall be incapableof causing ignition in normal operation, with a single fault, and withany combination of two faults applied, with the following safetyfactors:

1.5: in normal operation and with single fault.1.0: with only combination of two faults

The following example is given to explain the definition

Figure 4-5 4-20mA Transmitter

Figure 4-5 shows a 4-20 mA transmitter located in the most dangerous gaseousatmosphere. The minimum energy required to ignite the atmosphere is 20 µJ. To beclassed as Ex ia II C the barrier must;

1) In normal operation and with one fault (e.g. too much current) break the

circuit before 15 µJ can be released.

2) With two faults (e.g. too much current and too much voltage) break the

circuit before 20 µl can be released,

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -

H a z

a r d o u s a r e a s

& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 13/21


A practical example of how this works is given below.

If the supply voltage is 24Vd.c. with a current of 20mA then the power available is :

In order for the barrier (fuse) to be intrinsically safe Ex ia, the fuse must break in4µs

Ex ib has the same definition as Ex ia except that it only protects against one fault.Ex ib can only be used in Zone 1. A typical example of Ex ib equipment is the newerENTIS-ENRAF tank level transmitters.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 14/21


4.7 THE SAFETY BARRIER

4.7.1 One Way Barrier

The safety barrier makes sure that any fault in the safe area (control room) cannotprovide enough energy to ignite the gaseous atmosphere in the hazardous area.However, the system will not be intrinsically safe unless all the equipment in theloop is also intrinsically safe (e.g. the transmitter is also Ex ia IIC UP is Ex ia IICetc.)

A typical one way safety barrier is shown in Figure 4-6. This is used mainly as asafety barrier for switch (digital) circuits.

Figure 4-6 Safety Barrier

The barrier consists of a series resistor and fuse plus a Zener diode to earth. Theseries resistor limits the current to about 100mA from a 28V supply when thehazardous terminals are short circuited. The Zener diode operates in the region of30V and the fuse is rated at around 30 mA. The barrier thus ensures that either too

much current or too much voltage will blow the fuse. This will keep any dangerousenergy levels away from the hazardous area.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 15/21


4.7.2 Two Way Barrier

The one way barrier is not suitable for 4-20mA loops which are floating (neither side

connected to earth). Figure 4-7 below shows a typical barrier used with a floatingsupply.

Figure 4-7 Two Way Barrier

This barrier has extra Zeners and resistors. The resistor R is actually 3 diodes inseries. When they are working normally they act like a resistor and allow the returnloop current to pass. If a fault occurs, it is possible for a dangerous reverse currentto flow. R then acts as a diode to stop the reverse current.

Note: The reverse rating for the diodes must be high, around 600V.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 16/21


It is important that the earthing is good, i.e. less than IΩ to ground. All the earthwires must also be earthed to the same point. If the earths are not to the same pointthen currents may circulate in the earth line. If this happens then it's possible that a

fault in other equipment will blow all the barriers in the system.

he diagram below shows a typical Zener barrier earthing system (see Figure-4-8).

Figure 4-8 Zener Barrier Earthing System

Note: All electrical earthing systems are normally checked and tested bythe electrical department.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 17/21


4.7.3 References

The above notes show the two basic types of barrier in use. There are other types

of barriers for special purposes. You must read the manual for the barriers on yourinstallation, for special applications. The workshop has a wall chart produced byMTL (Measurement Technology Limited) which summarises the rules for intrinsicsafety.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 18/21


4.8 MODERN TRENDS IN INTRINSIC SAFETY

If a digital system of transmission is used it is possible to use what is called

"galvanic isolation", (no electrical connection). Figures 4-9 & 4-10 shows twomethods of doing this.

Figure 4-9 The Opto-Isolator

Figure 4-9 shows a typical opto-isolator. The digital input signals from the fieldproduce pulses of light in the LED. These produce pulses of electrical currentthrough the photo-transistor. The electronic amplifier converts the pulses of currentinto a digital signal output for control purposes. The photo diode and transistorcome in a single package. They are fully insulated from each other. They are

manufactured to meet Ex ia standards.

Electro-Maqnetic Isolation

A transformer can provide galvanic isolation and produce the required outputsignals when the transmission system is a.c. However, it is difficult to design atransformer without interwinding capacitance. The relay is a more simple methodwhich uses electro-magnetic isolation. Figure 4-10 shows a system which can beused.

Figure 4-10

A signal energises the coil in the safe area. The magnetic field closes a relaycontact in the hazardous area. There is no electrical connection between the safe

area and the hazardous area. This is sometimes called "voltless switching".

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 19/21


4.9 PRACTICAL POINTS ON HAZARDOUS AREA EQUIPMENT

4.9.1 Testing a Barrier

Figure 4-11 Testing, a Barrier

To test the Zener safety barrier properly you need- speciatised test equipment. Youalso need to use pulse techniques to make sure that each Zener diode is workingcorrectly. If you try to test the device fully without the correct test gear you may blowthe fuse. You can assume that if the fuse in a barrier is not broken then the wholecircuit is working correctly. Therefore, the most reasonable on-site test is to checkthat the end to end resistance is the same as the resistance value printed on the

barrier (e.g. 300Ω). Figure 4-11 shows an ohmmeter used to check a dual barrier.Note that the driving voltage from the ohmmeter must be 9 volts or less. Remember

that there are diodes in the barrier so only the correct polarity of ohmmeter supplywill indicate the barrier resistance.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 20/21


4.9.2 Flameproof Equipment

The following is a basic explanation of "flameproofing". This technique is of more

interest to the electrician but you should follow the basic rules written at the end ofthis section.

Figure 4-12 Flameproof Box

It is not practical to seal all equipment in hazardous areas (maintenance will berequired from time to time). So, there is a system which allows for a controlledexplosion. This system stops the resulting flame from igniting the hazardous area

atmosphere around the equipment.

Figure 4-12 shows a simple equipment box. The lid is fixed so that there is a smallgap between the lid and the box. The combustion gases from the explosion canescape from the box, but the flame will be extinguished before it reaches the endsof the flanges. Experiments done using a 25mm flange have given a standard sizefor the working gap. The following table gives sample values from the I.E.Cregulations.

GAS GROUP GAP

I0.5 mm

Il A 0.4 mm

H B 0.2 mm

H C 0.025 mm

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

Page 21/21


4.9.3 Basic Rules

1) When you replace the lid after servicing, make sure all the seals are fitted

correctly and the lid is tightened down evenly. Check the gap is the correctsize all round.

2) Never make extra holes in Ex d fittings. Any damage to the box or lid makesthe box unsafe.

3) Any part which is changed in Ex d equipment must be replacedwith a part which has the same safety factor as the original part.

4) Follow the instructions on the label about cleaning, cable sizing etc.

M o

d u

l e

N o .

3 :

I n s

t r u m e n

t a t i o n

3

U n

i t N o .

4 -


& i n t r i n s

i c s a

f e t y



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 4

INDUSTRIAL ELECTRONICS 1



July 1999- Rev.0

Page 1/16



UNIT 1 THE ELECTRICAL CIRCUIT

UNIT 2 SERIES AND PARALLEL CIRCUITS

UNIT 3 ELECTROMAGNETIC PRINCIPLES

UNIT 4 BASIC ELECTROSTATICS AND THE CAPACITOR

UNIT 5 THE INDUCTOR, CAPACITOR AND D.C.

UNIT 6 A.C. PRINCIPLES

UNIT 7 COMMON ELECTRICAL SYMBOLS


M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 2/16


TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 THE ELECTRICAL CIRCUIT 4

1.2.1 The Electrical Supply 4

1.2.2 Connecting Wires 4

1.2.3 Electrical Loads 5

1.3 ELECTRICAL MEASUREMENT 5

1.4 THE LAWS OF ELECTRICITY 6

1.4.1 Electrical Power 7

1.4.2 Electrical Energy 8

1.5 RESISTANCE AND RESISTIVITY 9

1.5.1 Resistance 9

1.5.2 Resistivity 9

1.6 WORKED EXAMPLES 11

1.6.1 Example 1 12

1.6.2 Example 2 12

1.6.3 Example 3 13

1.6.4 Example 4 14

1.7 KIRCHHOFF'S LAWS 15

1.7.1 First Law 15

1.7.2 Second Law 15

1.8 SUMMARY OF IMPORTANT FORMULAS 16

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 3/16




• Draw a basic electrical circuit and place AMMETERS and VOLTMETERScorrectly.

• State OHM'S LAW and perform simple calculations using OHM'S LAW.

• State the formulas for ELECTRICAL POWER and ENERGY. Carry outsimple calculations using these formulas.

• State the units in common use for electrical CURRENT, VOLTAGE,POWER, ENERGY and RESISTANCE.

• Explain RESISTIVITY and its unit.

• State KIRCHHOFF'S LAWS.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 4/16


1.1 INTRODUCTION

The aim of this unit is to introduce the basic concepts of electricity to a traineebeginning a career in Instrumentation.

1.2 THE ELECTRICAL CIRCUIT

Figure 1-1 The Electrical Circuit

Figure 1-1 shows the basic electrical circuit. It consists of an electrical supply, aswitch and a lamp (the electrical load). The parts are connected with insulated wires(conductors).

1.2.1 The Electrical Supply

The electrical supply provides the electro-motive force (EMF) to drive the electricalcurrent through the load. There are different forms of electrical supply.

• Batteries, provide a constant force, called Direct Current (D.C.). The currentflows from the positive terminal (red) to the negative terminal (black).

Two examples of batteries are the dry cell (Walkman battery) which is notrechargeable and the lead-acid battery (car battery) which is rechargeable.

• Alternating supplies provide a changing positive and negative force called Alternating Current (A.C.).

The wall sockets around the workshop are examples of an A supply.

1.2.2 Connecting Wires

The connecting wires, are made from material which allows electrical current topass through it (conductors). Copper, aluminium and silver are good conductors.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 5/16


The conductors must be insulated, to prevent accidents.

An insulator stops the passage of an electrical current. Typical examples are the

plastics (PVC, PTFE, etc.) and paper.

1.2.3 Electrical Loads

The load in an electrical circuit is a device which uses electricity. The most commonelectrical load is a lamp. The electric current passes through the lamp and produceslight. Other loads in the home are televisions, microwaves, and toasters. In industry,electric motors, industrial heaters and electrical/electronic instrumentation arecommon electrical loads.

1.3 ELECTRICAL MEASUREMENT

• The electrical circuit in Figure 1-1 shows the position of the two maininstruments used for electrical measurement.

The Ammeter measures the electrical current flowing throughthe circuit. It is connected in series (as shown). It measuresthe current in a unit called THE AMPERE (Amp).

The Voltmeter measures the electro - motive force (EMF) ofthe supply. It is connected in parallel across the load (Ssupply (as shown). It measures the EMF in a unit called THEVOLT.

.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t

A

V

WARNING:

You must connect these meters as shown in the diagram. If you connect themwrongly you may damage the circuit



July 1999- Rev.0

Page 6/16


1.4 THE LAWS OF ELECTRICITY

The first and most important law of electrical engineering is OHM's LAW.

"The current in an electrical circuit is proportional to the electro motive - forceapplied"

This can be written as

Figure 1-2 Ohm's Law Triangle

If you cover one of the quantities you can see how the other two will give you theanswer.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 7/16


Example:

1.4.1 Electrical Power

The power (P) of the circuit is the multiplication of the voltage supplied and thecurrent flowing.

P =IV = VOLTS x AMPS

The unit of electrical power is called the

WATT

Note:- Electrical power is related to mechanical power by the formula.

1 HORSE POWER = 746 WATTS.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 8/16


1.4.2 Electrical Energy

The energy (work) provided by an electrical circuit is

WORK = POWER x TIME

W = VOLTS x AMPS x SECONDS

The unit is called the

JOULE

Note:- One JOULE is a very small amount of electrical energy. Normally,electrical energy is paid for in "electrical units". One electrical unit (The

Kilowatt Hour) is 3,600,000 Joules.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 9/16


1.5 RESISTANCE AND RESISTIVITY

1.5.1` Resistance

1.5.2 Resistivity

An "OHMMETER" is a device for measuring the "RESISTANCE" in a circuit. You willpractice using it in the workshop. The following points must be remembered.

• Conductors have very low resistance (less than 1Ω)

• Insulators have very high resistance (more than 10,000,000 Ohm's)

• Loads have a resistance fixed during manufacture. A fault will cause eitheran open circuit (very high resistance) or a short circuit (zero resistance)

RESISTIVITY is a physical property of a material. The resistivity of a conductor isvery low and the resistivity of an insulator is very high. The resistivity of a material isfound by measuring the resistance of one cubic metre of a material between twofaces. The unit of resistivity is then the OHM METRE.

Typical examples for resistivity are:

Resistivity of copper = 1.725 x 108 Ωm

Resistivity of PVC = 1.2 x 10 10

Ωm

Resistivity is important because different types of conductor and insulator materialsare used in instrumentation. The following points must be remembered whenchanging conductors/insulators and laying new cables.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 10/16


• Changing the conductor material will change the conductor resistance (forexample aluminium has about twice the resistivity of copper)

• The longer the conductor (cable) the higher its resistance.

• The thinner the conductor (cross sectional area) the higher the conductorresistance.

So, a long thin cable has more resistance than a short thick cable.

Example :

Question

A copper cable has a resistance of 5Ω , a cross sectional area of 4mm2 and a

length of 500 m. What would be the resistance of an 8 mm2 aluminium cable(resistivity two times copper) of the same length ?

Solution

As aluminium has twice the resistivity of copper, the aluminium cable's resistance

will be 2 x 5Ω for the same size. However, the cross sectional area of the aluminium(8 mm

2) is two times that of the

copper(4 mm2) so its resistance will be half the copper cable 2 x 5

--------- Ω

2

Aluminium has more RESISTIVITY than copper but the RESISTANCE in the twocables is the same. This is because the aluminium cable is thicker than the copperone.

So, the aluminium cable has the same resistance as the copper one.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 11/16


1.6 WORKED EXAMPLES

The following worked examples are given to show how this theory is used, The

examples use standard multiples and sub multiples. The following list is included asa reminder.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 12/16


1.6.1 Example 1

Question:

A load has a resistance of 500Ω. If the supply current is 2 Amps, find the supplyvoltage?

Solution:

OHM's LAW EQUATION

V = IR

V = 2A x 500 Ω = 1,000 V

The supply Voltage = 1,000 Volts.

1.6.2 Example 2

Question:

An electric circuit has a supply current of 20mA and supply voltage of 3kV. Find:

a) The resistance

b) The power used by the load.

Solution:

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 13/16


b) The power equation is :

1.6.3 Example 3

Question:

An electric water heater has a rated power of 3.3 kW. If the supply voltage is 220Vfind:

a) The supply current

b) The resistance of the heater.

Solution:

a) The power equation is

b) From the Ohm's Law triangle.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 14/16


1.6.4 Example 4

Question:

An electric light bulb has a resistance of 50Ω. If the supply voltage is 200V, find:

a) The supply current

b) The power rating of the bulb.

c) The energy used in one hour.

Solution:

a) From the OHM'S LAW TRIANGLE

b) The power formula is

P = IV

= 4 x 200 = 800

The power rating of the bulb = 800 W

c) The energy formula is

P = CURRENT x VOLTAGE x SECONDS

= 4 x 200 x 60 x 60

= 2,880,000 JOULES

The energy used in one hour = 2.88MJ

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 15/16


1.7 KIRCHHOFF'S LAWS

Kirchhoff's laws are extensions of Ohm's law. You must remember them. They will

be used in the next unit on series and parallel circuits:

1.7.1 First Law

Figure 1-3 Kirchhoff's First Law

"The sum of electric currents flowing into a point (X) in an electrical circuit equalsthe sum of the electric currents flowing out of that point" Thus from Figure 1-3

1.7.2 Second Law

"The sum of the voltages around a circuit must equal the supply EMF"

Figure 1-4 Kirchhoff's Second Law

Thus from Figure 1-4

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t



July 1999- Rev.0

Page 16/16


1.8 SUMMARY OF IMPORTANT FORMULAS

OHM'S LAW V = IR

I = V / R

R = V / I

POWER = I V = I2 R = V

2 / R Watts

ENERGY = AMPS x VOLTS x SECONDS Joules

1 kWh = 3.6 MJ

KIRCHHOFF'S LAWS

First Law:

At a point in a circuit: Currents in = Currents out

Second Law:

Supply EMF = Sum of voltages around the circuit.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

1 -

T h e e

l e c

t r i c a

l c i r

c u

i t














M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 THE SERIES CIRCUIT 4

2.3 SERIES CIRCUIT EXAMPLES 5

2.3.1 Example 1 5

2.3.2 Example 2 6

2.3.3 Example 3 7

2.4 THE PARALLEL CIRCUIT 8

2.5 PARALLEL CIRCUIT EXAMPLES 9

2.5.1 Example 1 9

2.5.2 Example 2 10

2.6 SERIES AND PARALLEL COMBINATION CIRCUITS 11

2.6.1 Example 1 11

2.6.2 Example 2 13

2.7 MEASUREMENT PROBLEMS 15

2.8 WHEATSTONE BRIDGE 17

2.8.1 The Bridge Circuit 17


M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s







• State the formula for resistors in series.

• State the formula for resistors in parallel.

• Carry out simple calculations on series, parallel and series-parallelcombination circuits.

• Sketch a typical Wheatstone bridge and calculate the value of the unknownresistor.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.1 INTRODUCTION

The aim of this unit is to explain the three common circuits used in instrumentelectrical work. The series circuit, the parallel circuit and the Wheatstone bridge.

2.2 THE SERIES CIRCUIT

Figure 2-1 The Series Circuit

Figure 2-1 shows an example of the basic series circuit with four loads (resistors)connected to a supply.

The rules for this circuit are:

a) Kirchhoff's second law applies. The supply voltage equals the sum of thevoltages around the circuit.

b)

b) The supply current is the same in all parts

c) The TOTAL RESISTANCE of the circuit is the SUM OF THE INDIVIDUALRESISTORS around the circuit.

d)

NOTE: The series circuit is not used much in industry because it has seriousdisadvantages.

• If extra loads are added to the circuit the voltage across each loadwill fall.

• If one load is broken (open circuit) the supply is cut off to all the loadson the circuit.

However the series circuit is used for the basic instrument electrical signal circuit

(loop). This circuit will be shown during the instrument course.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.3 SERIES CIRCUIT EXAMPLES

The notes above give the rules for a series circuit. The example circuit has fourloads. The following worked examples show the steps required to find unknownquantities in series circuits.

2.3.1 Example 1

Question

Two 100Ω loads are connected in series to a 100V supply. Find

a) The total circuit resistance

b) The supply current.

Solution

Circuit Diagram

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.3.2 Example 2

Solution:

Using the circuit diagram given above. Find :a) The supply current (Is) b) The power

of the 40Ω load.

Total circuit resistance = 50EI + 1 M + 40Ω

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.3.3 Example 3

Question:

30 lights are connected in series across a 210V supply. Find the voltage across

each bulb and the supply current if the resistance for each bulb = 2.93Ω

Solution:

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.4 THE PARALLEL CIRCUIT

Figure 2-2 The Parallel Circuit

Figure 2-2 shows as an example the arrangement for three parallel electrical loads.The rules of this circuit are:

a) In this case Kirchhoff's first law applies, "Currents into a point on anelectrical circuit equal the currents leaving that point " so that

The supply current increases as more loads are added in parallel.

b) The supply voltage will be the same for each load.

c) The total resistance of the circuit (RT) is given by the equation.

Note: The parallel circuit is the standard industrial circuit because

• The supply voltage is the same for each load.

• If one load is disconnected (open circuited) the other loads will still work.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.5 PARALLEL CIRCUIT EXAMPLES

The notes above give the rules for a parallel circuit. The example circuit has threeloads. The following worked examples show the steps required to find unknownquantities in a parallel circuit.

2.5.1 Example 1

Question:

Two 100Ω loads are connected in parallel to a 100V supply. Find

(a) The total circuit resistance.

(b) The supply current.

Solution:

Circuit Diagram.

(a) The total circuit resistance is found using the formula given.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.5.2 Example 2

Question

An electrical circuit consists of three loads connected in parallel across a supply asshown in the circuit diagram above. Find

a) The supply voltage (Vs)

b) The supply current (Is)

Solution :

In a parallel circuit the supply voltage is the same for each load so with 1A flowing

through the 10Ω resistor.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.6 SERIES AND PARALLEL COMBINATION CIRCUITS

It can be difficult to calculate unknown quantities in a series and parallelcombination circuit. The following examples show ways of finding the answers.

2.6.1 Example 1

Question :

Using the circuit diagram above calculate

a) Total circuit resistance

b) Supply current (Is)

c) The voltage across each resistor.

Solution:

a) Work out the total resistance of the parallel part first.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





b) Redraw the circuit using the parallel result.

Total series resistance = 10Ω + 12.Ω = 22Ω

c) Supply current

Supply current = 4.55A

d) Voltage across the 10Ω

resistor.

V 10Ω = Is x 10

= 4.55A x 10Ω

V10Ω = 45.5 V

e) Voltage across 20Ω and 30Ω resistors will be the supply current times theparallel total resistance

V20Ω or V 30 Ω = Is x 12

= 4.55A x 12Ω

V20Ω or V 30 Ω = 54.6 V

Note: To check your answer, add V20Ω to V10Ω The result should be V SUPPLY withinthe accuracy of the calculator.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.6.2 Example 2

Using the above diagram calculate the supply voltage if Is = 2A

Solution:

a) Work out the total resistance of each branch first.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





b) Draw the new circuit

c) The supply voltage

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.7 MEASUREMENT PROBLEMS

Figure 2-3 Using an Ammeter and Voltmeter

Figure 2-3 shows a circuit with an ammeter (in series) and voltmeter (in parallel)measuring the circuit current and potential difference (PD) across the load. Anothercircuit can be drawn which includes the resistance of the meters (see Figure 2-4)

Figure 2-4 Equivalent Circuit with Ammeter and Voltmeter Added

For true readings the value of R A must be very small and Rv very big. Otherwise,the current and voltage readings are all wrong because the meters change circuitvalues.

Normally the ammeter causes no problems as it has a very low resistance.However, the voltmeter can cause problems, especially the old type of moving coilmeter. An example is given below.

The diagram shows a voltmeter (resistance 10kΩ) used to measure the PD acrossR2.

Current with voltmeter not connected.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





Voltage across R2 with voltmeter not connected.

Current with voltmeter connected

Voltage across R2 with voltmeter connected

From the example it can be seen that using a voltmeter of low resistance changesthe readings a lot. Most measurements in instrumentation must be carried out with a

digital voltmeter (DVM), with a high input resistance (> 10MΩ). If the voltmeter doesnot have a high input resistance the measurements will not be correct.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





2.8 WHEATSTONE BRIDGE

The Wheatstone bridge is widely used in instrumentation to measure resistance

accurately. It is also used to show changes in the resistance of sensors used tomeasure pressure, level, temperature, etc. The following notes explain the basicprinciple of the Wheatstone bridge. Practical applications will be shown later in thetraining .

2.8.1 The Bridge Circuit

Figure 2-5 The Wheatstone Bridge

The Wheatstone bridge circuit (see Figure 2-5) consists of two very accurate(standard) resistors(R

l & R

2) called the ratio arms. There is an accurate variable

resistor (Decade Box R3). A very sensitive ammeter which will detect very smallcurrents (called a Galvanometer (G)) is connected across points D and B. A supplyvoltage is connected across points A and C. There are also two terminals toconnect an unknown resistor Rx across the points A and B.

The value of the unknown resistor is given by the equation.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s





Theory:

The value of the unknown resistor is found by adjusting the value of the variable

resistor until the galvanometer reads zero. This is called the balanced position sothat at balance when I3 = 0

This is the balance equation for a Wheatstone bridge and must be remembered.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s






Resistors in Series

RT = R1+ R2 + R3 etc.

Resistors in Parallel

1 / RT : =: 1 / R1 + 1 / R2 + 1 / R3 etc.

Wheatstone Bridge

Rx = Ratio Arms x Decade Box Value.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o

. 2 -

S e r i e s

& p a r a

l l e l c

i r c

u i t s














M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 BASIC MAGNETICS 4

3.3 THE ELECTRIC CURRENT AND MAGNETIC FIELDS 5

3.4 SOLENOID APPLICATIONS 6

3.4.1 The Relay 6

3.4.2 The Solenoid Valve 7

3.5 INTRODUCTION TO ALTERNATING CURRENT (A.C) 8

3.6 MOTOR PRINCIPLE 11

3.6.1 The Moving Coil Meter 11

3.7 SELF AND MUTUAL INDUCTANCE. 12

3.7.1 Self Inductance 12

3.7.2 Mutual Inductance 12

3.7.3 The Transformer 13

3.7.4 Example 14


M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s







• State the basic rules for magnets

• Sketch typical magnetic fields around magnets.

• Sketch the magnetic field produced by an electric current.

• Sketch the magnetic field produced by a solenoid and give examples of itsuse.

• Explain generator principle and the production of an alternating current

waveform.

• Explain the terms RMS, peak, peak to peak, cycle and frequency of an A.C.waveform.

• State the standard workshop supply.

• Explain, in simple terms, motor principle using the moving coil meter.

• Explain self and mutual inductance; the Henry.

• Explain the action of a transformer and state the formula used.

• Carry out simple calculations using the transformer equation.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.1 INTRODUCTION

The aim of this unit is to introduce the electric current and its magnetic field.

3.2 BASIC MAGNETICS

Magnetic materials produce magnetic fields as shown below. Only three materialscan be made to produce a large magnetic field.

a) Iron

b) Cobalt Ferro - magnetic elements

c ) Nickel

Rules

1) Magnetic lines go from N to S.

2) Magnetic lines never cross

3) Like poles repel

4) Unlike poles attract.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.3 THE ELECTRIC CURRENT AND MAGNETIC FIELDS

When a current is passed through a conductor it will produce a magnetic field, as

shown in the diagram.

Current (+) into the paper; the Current (0) out of the paper; thefield is clockwise. field is anti-clockwise.

The magnetic field around a conductor can be increased by increasing the current.However, a better method of increasing the magnetic field produced by electricity isto make a solenoid. A solenoid is made by coiling insulated wire around a cylinder.The greater the number of turns in the coil, the greater the magnetic field produced(see Figure 3-1).

Figure 3-1 The Simple Solenoid

When a current is passed through the coil, the magnetic field is concentrated. Thisfield has a pattern similar to a bar magnet with N and S poles as shown.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





Note:

(a) Reverse the current flow and the polarity reverses.

(b) Reverse the direction of the turns in the coil and the polarity reverses.

(c) Normally it is impossible to tell the direction of the turns in the coil. If youwant to reverse the polarity, reverse the current flow.

3.4 SOLENOID APPLICATIONS

3.4.1 The Relay

A typical relay is shown in Figure 3-2.

Figure 3-2 The Relay

The relay consists of a solenoid and contacts. When the solenoid is energised itattracts a piece of iron (the armature) which changes over a set of contacts. Themagnetic core of the solenoid is made of a material which is magnetic only whencurrent flows through the coil (a temporary magnet). When the coil de-energises thereturn spring pulls the armature back and the contacts return to their normalpositions. Relays operate using A.C or D.C supplies. The coils have many turns ofsmall diameter insulated wire. This gives a strong magnetic field from a smallenergising current.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.4.2 The Solenoid Valve

The solenoid valve is an on-off device used to control the flow of liquids and gases

through piping. When the supply voltage is applied to the coil, the solenoid isenergised. It attracts the valve plunger and the valve opens. When the solenoid isde-energised the return spring closes the valve. A typical solenoid valve is shown inFigure 3-3.

Figure 3-3 The Solenoid Valve

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.5 INTRODUCTION TO ALTERNATING CURRENT (A.C)

Figure 3-4 The Simple A.C Generator

Figure 3-4 shows a simple alternating current generator. The single turn coil,rotated in the magnetic field, has an alternating voltage induced in it to produce analternating current in the load resistor (R). The size of the voltage depends on thefollowing:

(a) The strength of the magnetic field.

(b) The speed of the rotating coil.

(c) The length of the coil in the magnetic field.

(d) The number of turns on the coil.

(e) The voltage is maximum when the coil is at right angles to the magnetic field(moving across). The voltage is at zero when the coil is parallel to themagnetic field,- (moving in the same direction). See figure 3-5.

(f) Industrial electric generators normally keep the coils steady and rotate thefield. The output will still be the same.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





Figure 3-5 The A.C Waveform

Figure 3-5 shows, in simple terms, a single rotation of a coil in a magnetic field:

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





Position A Horizontal. The coil is moving parallel to the field. Zero voltsinduced

Position B Vertical. The coil has rotated 90°. Maximum induced voltage.

Position C Horizontal. The coil has rotated 180°. Zero induced voltage

Position D Vertical. The coil has rotated 270°. Maximum inducedvoltage. The voltage is in the opposite direction as the coil isreversed in the field.

Position A Back to position A. The coil has rotated 360° and completedone cycle.

The voltage between the given points changes to . produce what is called aSINEWAVE. A complete rotation through 360° is called a CYCLE. The number ofcycles per second is called the FREQUENCY and is measured in HERTZ (Hz).Meters measuring A.C voltages and currents are set up to give the D.C equivalent.This is called the ROOT MEAN SQUARE (RMS) value. It is given by the formula:

Note:

Electrical devices using an A.C supply have a fixed frequency. The standardfrequency is 50Hz or 60 Hz , The voltage of a domestic supply is also fixed 120 or140V. Make sure that electrical equipment used in the workshop is set to work at240V@ 50Hz, otherwise you may damage the equipment.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.6 MOTOR PRINCIPLE

MOTOR PRINCIPLE is the reverse of GENERATOR PRINCIPLE described in the

previous section, In an electric motor the current is applied to a coil placed in amagnetic field. This makes the coil rotate and rotates the mechanical loadconnected to it. The construction and operation of industrial electrical motors iscomplicated. They are studied by electrical technicians.

3.6.1 The Moving Coil Meter

A simple example to show motor principle is the moving coil meter shown in Figure3-6.

Figure 3-6 The Moving Coil Meter

When a D.C current is passed through the coil the coil moves, by motor principle,against the controlling spring. When the force produced by motor principle equalsthe force of the controlling spring, the position of the needle on the scale shows thesize of the current.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.7 SELF AND MUTUAL INDUCTANCE.

3.7.1 Self Inductance

Figure 3-7 The Inductor

Self inductance occurs when a coil is supplied with an alternating current (seeFigure 3-7). The changing magnetic field cutting the coil produces a back EMFwhich opposes the supplied current. The size of the back EMF depends on theconstruction of the coil and the rate of change of the supplied current. Written as anequation.

Back EMF(e) = A constant for the coil x rate of change of current.

The coil constant is called its SELF INDUCTANCE and is measured in a unit called

the HENRY. The symbol for self inductance is L.

3.7.2 Mutual Inductance

M

MUTUAL INDUCTANCE is the property of two coils placed side by side so that themagnetic field in one coil cuts the other one. When an A.C supply is connected tothe primary coil the changing magnetic field cuts the secondary one. By generatorprinciple this induces a voltage in the secondary coil. The amount of EMF producedin the secondary depends on the MUTUAL INDUCTANCE between the two coils,measured in HENRYS.

The symbol for mutual inductance is M

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.7.3 The Transformer

The transformer is a practical example of mutual inductance. The mutualinductance is made as high as possible by winding one coil on top of the other on atemporary magnetic core. All the magnetic field produced by the primary coil cutsthe secondary coil. The secondary output voltage depends on the turns ratio of the

two coils. Assuming no losses (100% efficient), the transformer equation is asfollows:

Note:

(1) If VP or NP is greater than Vs or Ns it is a STEP DOWN transformer.

(2) If Vs or Ns is greater than VP, or Np it is a STEP UP transformer.

(3) transformer only works with an A.C supply. A D.C supply will produce nochanging magnetic field or back EMF. The resistance to D.C. is very low sothe transformer will burn out.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s





3.7.4 Example

Question:

A transformer has 500 turns on the primary coil and 27 turns on the secondary coil.The supply voltage is 240V and the secondary load current is 10 A. Find the:

(a) Secondary voltage

(b) Primary current.

Solution:

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s






V RMS = 0.707 V PEAK

I RMS = 0.707 I PEAK

Transformer Equation

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

3 -

E l e c

t r o m a g n e

t i c p r i n c i p

l e s














M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r





TABLE OF CONTENTS

Para Page


4.1 INTRODUCTION 4

4.2 THE CAPACITOR 4

4.2.1 Capacitor Construction 5

4.2.2 Examples Of Capacitor Types 5

4.3 CAPACITOR CONNECTIONS 6

4.3.1 Series 6

4.3.2 Parallel 6

4.4 EXAMPLES ON CAPACITANCE 7

4.4.1 Example 1 7

4.4.2 Example 2 7

4.4.3 Examples 3 8


M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r







• Sketch a simple capacitor

• State the basic formulas for a capacitor Q = CV, C = ε A/d. Understand theunit of capacitance; the Farad.

• State the formula for capacitors in series.

• State the formula for capacitors in parallel.

• Carry out simple calculations on capacitors in series and parallel

• State the formulas for energy stored in a capacitor.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r





4.1 INTRODUCTION

The previous section (Unit 3) dealt with basic electro-magnetism. The ability of an

electric current to produce energy in the form of a magnetic field. This unit will dealwith the CAPACITOR; a device which stores electrical energy as an ELECTRICFIELD.

4.2 THE CAPACITOR

Figure 4-1 The Capacitor

Figure 4-1 shows the simplest form of a capacitor. It consists of two conducting

plates separated by an insulator (dielectric). When a voltage (V) is applied acrossthe plates the insulator will take in a charge and produce an electric field betweenthe plates. The charge (Q) taken in is given by this equation

Q = C V

C is called the CAPACITANCE of the device. The unit of measurement is theFARAD (F).

Q The total charge stored has a unit called the COULOMB (C).

V Is the voltage applied across the plates.

Total charge is also given by the equation

Q = AMPS. SUPPLIED x SECONDS

The electrostatic energy in a capacitor is given by the equation

Note : A battery stores electrical energy by chemical means. A car battery is

measured by the charge stored in Ampere-Hours (Ahr). A 30 Ahr battery willstore

30 x 3600 = 108,000 Coulombs. M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r





4.2.1 Capacitor Construction

The capacitance of a capacitor depends upon the following factors.

• The area of the plates (A).

• The distance between the plates (d). The closer the plates, the higher thecapacitance.

• The dielectric strength of the insulator (ε).

This gives the equation

It is difficult to make large values of capacitance. Usually the plates and insulatorare rolled up and placed in a can to increase the value of capacitance. Thedielectric can also be made from chemicals (e.g. Tantalum and Aluminium oxides).This reduces the dielectric thickness to millionths of a metre (micron). Thisincreases the capacitance value because the plates are closer together.

4.2.2 Examples Of Capacitor Types

• Electrolytic Dielectric :

Aluminium and Tantalum. Approximate range of values from 0.1µF to 1 F.These are usually polarised and must be fitted correctly when used with D.C.The positive and negative sides are clearly marked.

• Plastic Dielectric :

Polypropylene, Polycarbonates, Polyester. Approximate range of values

from 100 µF to 1 µF. Non-polarised.

• Ceramics, mica and air dielectric :

Very small values. Approximate range of values 1 µF to 1000µF.Non-polarised.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r





4.3 CAPACITOR CONNECTIONS

4.3.1 Series

Connecting capacitors in series has the same effect as pulling the two plates furtherapart.

The capacitance will go down. The formula is similar to resistors in parallel.

4.3.2 Parallel

Connecting capacitors in parallel has the same effect as enlarging the area of theplates .

The capacitance will go up. The formula is similar to resistors in series.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r





4.4 EXAMPLES ON CAPACITANCE

4.4.1 Example 1

Question

Find the charge stored in a 1 00µ F capacitor connected to a 100 V D.C. supply.

Solution :

The charge in a capacitor is given by the equation

Q = C V

Q = 100 X 10 -6

F x 100V

Q = 10-2

C

The charge stored = 0.01 C

4.4.2 Example 2

Question

Two 10,000 µF capacitors are connected in parallel across a 5,000 D.C. supply.Find

(a) The total capacitance of the circuit.

(b) The charge stored.

Solution :

(a) Using the equation for capacitors in parallel

CT = C1 + C2

= 10,000 µF= + 10,000 µF

= 20,000 µF.

Total capacitance = 20,000 µF

(b) Stored charge equation is

Q = CV

Q = 20,000 x 10-6

F x 5000V

Q = 100C

Stored charge = M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r

100 Coulombs





4.4.3 Examples 3

Question

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r






For a Capacitor

C = ε A / d

Q = CV

Series connection:

1 / CT = 1 / Cl + 1 / C2 + 1 / C3 etc.

Parallel connection:

CT = Cl + C2 + C3 etc.

Energy stored

W = 1/2 C V 2

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

4 -

B a s

i c

e l e c

t r o s

t a t i c s

& t h e c a p a c

i t o r














M o d u l e

N o . 4 : I n d u s t r i a l e l e c t r o n i c

s 1

U n i t N o . 5 -

T h e i n d u c t o r , c a p a c i t o r &

D C





TABLE OF CONTENTS

Para Page


5.1 INTRODUCTION 4

5.2 D.C AND THE INDUCTOR 4

5.3 D.C. AND THE CAPACITOR 6

5.3.1 Circuit Operation 7

5.4 CAPACITOR TIMING CIRCUITS 7

5.4.1 Example 8


M o d u l e


s 1

U n i t N o . 5 -


D C







• Explain with the aid of a diagram D.C. applied to an inductor.

• Explain with the aid of a diagram D.C. applied to a capacitor.

• Explain the time constant of a resistor - capacitor circuit and its use as anelectronic timing circuit.

M o d u l e


s 1

U n i t N o . 5 -


D C





5.1 INTRODUCTION

Units 2 and 3 explained the rules to be used when dealing with resistive circuits.The calculations can be carried out using either D.C. values or A.C RMS. values.The results will be the same. This is not true when inductors and capacitors areincluded in a circuit. This unit will explain what happens when D.C is applied to aninductor and capacitor.

5.2 D.C AND THE INDUCTOR

Figure 5-1 The Electrical Circuit

Figure 5-1 shows D.C applied to an inductor via a switch. The graph below showswhat happens when the switch is closed.

M o d u l e


s 1

U n i t N o . 5 -


D C





At the moment the switch is closed the build up of the magnetic field in the coilproduces a back EMF which opposes the applied EMF The starting current is zero.

When the magnetic field is steady the back EMF is zero. The current is a maximumand is limited only by the winding resistance of the coil. The time it takes to reachmaximum current flow depends on the ratio of the coil inductance to its windingresistance. Because of this effect relay coils and the solenoids of electricallyoperated valves have increased resistance. This reduces excessive hold oncurrents.

If the switch is open the field in the coil collapses and a high voltage is produced.When the switch is open this high voltage can destroy the switch contacts bysparking. Therefore special circuits must be used to protect the switch and theconnected supply voltages. These circuits will be explained in Industrial Electronics11.

Note:

1. The above principle is used to ignite the fuel of a gasoline engine. Thevoltage produced when the circuit of an energised coil is broken is used tomake a spark across the plug fitted in the cylinder.

2. An energised coil stores energy in a magnetic form. The energy stored isgiven by the equation

W = 1/2 L I2

M o d u l e


s 1

U n i t N o . 5 -


D C





5.3 D.C. AND THE CAPACITOR

Figure 5-2 D.C Applied to a Capacitor

Figure, 5-2 shows D.C applied to a capacitor. Switch A closed and switch B opencharges the capacitor. Switch A open and Switch B closed discharges the capacitor.The graph below shows what happens when the switches are operated.

M o d u l e


s 1

U n i t N o . 5 -


D C





5.3.1 Circuit Operation

Charging:

When switch A is first closed the current flow into the capacitor is only limited by theloss resistance of the insulator. As the capacitor charges the current flow will fall tozero and the voltage across the capacitor will equal the supply voltage. This meansthat a charged capacitor is an open circuit to D.C.

Discharging:

When switch B is closed the discharge current is in the opposite, direction to thecharging current. It will start at maximum and then fall to zero as the capacitorvoltage falls to zero.

5.4 CAPACITOR TIMING CIRCUITS

The capacitor is often used in electronics as a timing circuit. An explanation of thebasic principle is given in Figure 5-3. We will look at how this circuit can be usedduring more advanced work in later units.

Figure 5-3 Basic RC Timing Circuit

Figure 5.3 shows a basic timing circuit using the voltage across the capacitor (C).The switch is closed and when the voltage (V) rises to a set value the timing unitoperates. It is normal to use what is called the time constant for the circuit. The time

constant is given by the equation.

TIME CONSTANT (T) RESISTANCE (R) x CAPACITANCE (C)

(SECONDS (OHMS) (FARADS)

The voltage across the capacitor will be 63.2% of the D.C supply voltage at the timeconstant (T = RC).

M o d u l e


s 1

U n i t N o . 5 -


D C





5.4.1 Example

Question:

A 1 MΩ resistor is connected in series with a 100µF capacitor and supplied withD.C. Find the time taken for the capacitor to reach 63.2% of its maximum valueafter the supply is switched on.

Solution:

The time to reach 63.2% of the supply voltage is the time constant of the circuit RC.

T.C = 1 X 106Ω X 100 X 10

6 F

Time Constant = 100 seconds.


TIME CONSTANT = RESISTANCE x CAPACITANCE

(SECONDS) (OHMS) (FARADS)

T = RC

M o d u l e


s 1

U n i t N o . 5 -


D C














M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





TABLE OF CONTENTS

Para Page


6.1 INTRODUCTION 4

6.2 A.C. AND THE INDUCTOR 4

6.3 A.C. AND THE CAPACITOR 5

6.3.1 The Inductor-Resistor Combination 6

6.3.2 The Capacitor-Resistor Combination 7

6.3.3 RL and C in Combination 8

6.3.4 Resonance 9

6.4 WORKED EXAMPLES 9

6.4.1 Example 1 9

6.4.2 Example 2 10

6.4.3 Example 3 10

6.4.4 Example 4 12

6.4.5 Example 5 13

6.4.6 Example 6 14

6.4.7 Example 7 15


M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s







• Explain with the aid of a diagram the effects of A.C. on an inductor.

• Explain with the aid of a diagram the effects of A.C. on a capacitor.

• State the formula for inductive reactance.

• State the formula for capacitive reactance.

• State the formulas for RL and C combination circuits supplied with A.C.

• Explain the term impedance.

• Carry out simple calculations using the formulas for RL and C combinationcircuits supplied with A.C.

• Explain resonance.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.1 INTRODUCTION

The aim of this unit is to explain the operation of a capacitor and an inductor whensupplied with A.C. both individually and in combination with resistors.

6.2 A.C. AND THE INDUCTOR

Figure 6-1 A.C. and the Inductor

The previous unit showed the effect of applying D.C. to an inductor. The back EMF

across the inductor falls from maximum to zero and the current rises from zero tomaximum. A.C. is a form of continuously switching D.C. The diagram and the graph(see Figure 6-1) show the effect of supplying A.C. to an inductor. The voltagewaveform leads the current waveform by 90'. When the voltage is maximum thecurrent is zero. When the current is maximum the voltage is zero and so on. Thefaster the A.C. changes (the higher the frequency) the greater the back EMF whichis produced. The back EMF reduces the current. The alternating current resistanceprovided by the coil is called INDUCTIVE REACTANCE (XL) and is given by theformula

XL = 2 f L Ohms,

XL = Inductive reactance (Ohms)

L = Coil inductance in Henrys (H)

f = Frequency in Hz

∏ = Mathematical constant (3.142).

This formula must be remembered.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.3 A.C. AND THE CAPACITOR

Figure 6-2 A.C. and the Capacitor

The previous unit showed the effect of applying D.C. to a capacitor. The chargingcurrent starts at a maximum and falls to zero and the voltage across the capacitorstarts at zero and rises to a maximum. The effect is the exact opposite to aninductor. The diagram (see Figure 6-2) shows the effect of supplying A.C. to acapacitor. This time the graph shows the current leading the voltage by 90'. Whenthe current is maximum the voltage is zero and so on.

The faster the A.C. changes (the frequency) the less time the capacitor has tocharge so the current through the device increases. The A.C. resistance(reactance) of a capacitor (Xc) goes down as the frequency goes up and is given bythe formula

Xc = I Ohms---------

2 ∏ f C

Xc = Capacitive reactance in Ohms

C = Capacitance in Farads (F)

f = Frequency in H2,

∏ = Mathematical constant (3.142).

This formula must be remembered.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.3.1 The Inductor-Resistor Combination

RL in series circuit RL in parallel circuit

Figure 6-3 Inductor - Resistor Combination

Figure 6-3 shows the series and parallel circuits of an RL combination. Calculatingthe unknown values of Vs and Is is difficult because the current and voltage

waveforms through the inductor are 90° apart.

The total A.C. resistance, IMPEDANCE (Z) for a series circuit is given by theformula:

A simple line diagram is used to illustrate the problem. From the diagram we get thefollowing formulas. These must be remembered.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.3.2 The Capacitor-Resistor Combination

Figure 6-4 Inductor - Capacitor Combination

Figure 6-4 shows the series and parallel circuits of an RC combination. Theformulas for the total A. C. resistance (IMPEDANCE) of the above circuits follow thesame principle as for the resistance and inductor circuits to give:

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.3.3 RL and C in Combination

Figure 6-5 shows the series and parallel circuits for an RLC combination. In thiscase the reactance of the reactive parts oppose each other to give the formulas.

Figure 6-5 Resistor - Capacitor - Inductor Combination

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.3.4 Resonance

When the value of XL equals the value of XC then XL - XC= 0. So the formula forimpedance changes to:

Therefore Z = R for both circuits

This effect is called RESONANCE. At one frequency the circuit is only resistive.

At resonance;

The frequency (f) is called the RESONANCE FREQUENCY of the circuit. Itproduces a circuit that is purely resistive.

This circuit is useful because it is used to select one frequency from all others. Arange of these circuits is used to select a television channel or radio station. Eachchannel transmits at a different frequency to stop interference

6.4 WORKED EXAMPLES

6.4.1 Example 1

Question

Find the inductive reactance of a 5 mH coil at 50 kHz.

Solution

Inductive Reactance (XL) = 2 ∏ f l

XL = 2 ∏ x 103 (Hz) 5 x 10

-3 (H)

XL = 500 ∏ Ω

XL = 1571 Ω

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





Inductive Reactance = 1571Ω





6.4.2 Example 2

Question

Find the capacitive reactance of a 1∏ capacitor at 50 kHz.

Solution

Capacitive Reactance (Xc) = 1--------

2 ∏C

Xc = 1-------------------------------------

2 ∏ 50 x103 (Hz ) x l x l 0

-6 (F)

= 103

-------- = = 3.183 Ω

100∏

Capacitive Reactance = 3.183 Ω

6.4.3 Example 3

Question

Find the impedance of a 50Ω resistor and 100 µF capacitor connected in series to a50 Hz supply.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.4.4 Example 4

Question

Find the impedance of a 50Ωresistor and inductive reactance of 50Ω connected inseries. ,

Solution

CIRCUIT DIAGRAM R = 50Ω

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.4.5 Example 5

Question

Using the diagram above, find the circuit impedance.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.4.6 Example 6

Question

Using the diagram above, find the circuit impedance.

Solution

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s





6.4.7 Example 7

Question

Using the circuit diagram above, find

(a) Resonant frequency

(b) Circuit impedance at resonance

Solution

a) At resonance

(b) At resonance XL cancels X. and the circuit is resistive only.

Circuit impedance = .10 Ω

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s






Ohm's law and A.C.

V = I R

V = I XC

V = 1 XL

V = IZ

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

6 -

A C P r i n c i p

l e s









UNIT 4 BASIC ELECTROSTATIC$ AND THE CAPACITOR





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o . 7

- C o m m o n e

l e c

t r i c a

l s y m

b o

l s





TABLE OF CONTENTS

Para Page

7 . COMMON ELECTRICAL SYMBOLS 3

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o . 7

- C o m m o n e

l e c

t r i c a

l s y m

b o

l s





7. COMMON ELECTRICAL SYMBOLS

ELECTRICITY AND MAGNETISM

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o . 7

- C o m m o n e

l e c

t r i c a

l s y m

b o

l s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o . 7

- C o m m o n e

l e c

t r i c a

l s y m

b o

l s





GRAPHIC SYMBOLS

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o . 7

- C o m m o n e

l e c

t r i c a

l s y m

b o

l s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o . 7

- C o m m o n e

l e c

t r i c a

l s y m

b o

l s














M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





TABLE OF CONTENTS

Para Page

PRACTICAL TASK 1 3

PRACTICAL TASK 2 6

PRACTICAL TASK 3 8

PRACTICAL TASK 4 10

PRACTICAL TASK 5 11

PRACTICAL TASK 6 12

PRACTICAL TASK 7 13

PRACTICAL TASK 8 16

PRACTICAL TASK 9 19

PRACTICAL TASK 10 22




RESISTANCE COLOUR CODES 35

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 1

PROOF OF OHM'S LAW

1. Connect the circuit as shown using the components supplied.

2. After the instructor has checked the circuit, switch on the D.C. supplyand set the supply voltage to 1V on the voltmeter. Write down thecurrent reading on the table provided.

3. Repeat step (2) for a D.C. supply setting of 2V to 10V- Increase thesupply in one volt steps. Note the current reading each time.

4. Switch off the D.C. supply.

5. Plot a graph of voltage against current from the readings obtained.

6. The graph must be a straight line to show Ohm's law. V α 1.

7. Find the slope of the graph.

8. The slope of the graph will be the value of the resistor.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





Slope = Distance X (Volts) = Resistance----------------------

Distance Y (mA)

RESULTS TABLE

Questions to be answered to show understanding. of the practical task.

(1) What is the current, if the supply voltage is 25 volts?

---------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------

(2) What is the circuit current with a supply voltage of 10 V, if the resistor is

changed to 300Ω

---------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 2

1. Connect the circuit as shown using the components supplied. Do notconnect the meters.

2. After the instructor has checked the circuit, set the supply voltage to10V with the voltmeter. Switch off.

3. Connect an ammeter across A-B. Switch on and note the ammeterreading. Switch off.

4. With the ammeter across A-B short out C-D. Switch on and note thereading. Switch off.

5. Short out A-B and connect the ammeter across C-D. Switch on andnote the reading. Switch off.

6. above readings should show that in a broken series loop, the currentis zero. Also the current is the same in all parts of a series circuit.

7. Short out A-B and connect an ammeter across C-D. Switch on.

8. Connect a voltmeter across P-Q, R-S and T-U in turn and note thereading of each. Switch off.

9. The voltage readings obtained will prove KIRCHHOFFs second law.

10. Divide the supply voltage (10V) by the total resistance (RT) for aseries circuit.

RT = 10OΩ + 20Ω + 30Ω = 60Ω

This will give the reading measured on the ammeter within the tolerance ofthe resistor values and the accuracy of the meters.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





RESULTS TABLE

Questions to be answered to show understanding of the practical task.

(1) What does the ammeter read, if the supply voltage is 5 volts?

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

(2) What happens to the voltage across the 20Ω resistor, if the short circuit

across AB is replaced with a 40Ω resistor?

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 3

THE PARALLEL CIRCUIT

1. Connect the circuit as shown, without the meters connected.

2. Set the D. C. supply to 10 V using the voltmeter. Switch off.

3. Short out G - H and place the ammeter across A-B. Switch on and note thereading. Switch off.

4. Repeat step (3) with the ammeter connected across C-D and E-F.

5. Short out A-B, C-D and E-F. Reconnect the short circuit on G-H and replace

with the ammeter across G-H. Switch on and note the reading. Switch off.

6. KIRCHHOFFs first law is now proved as

7. Short out G-H, A-B, C-D and E-F. Switch on. With a voltmeter measureVSUPPLY, VR1 VR2 and VR3

8. This will show that, in a parallel circuit, the voltage is the same across allloads.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





RESULT TABLE


(1) Calculate the resistance of the three resistors in parallel and find thesupply current (is) for a supply voltage of 10V. This answer should be,within the accuracy of the equipment, the same as the measured Is.

---------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------

(2) Are the measured values for 11, 12 and 1,3 the same as the following?

---------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 4

THE SERIES - PARALLEL COMBINATION CIRCUIT

1 .Connect the circuit as shown, without the ammeter connected.

2. After the instructor has checked the circuit, switch on the power supply. Setthe supply and voltage to 11 V. Switch off.

3. Connect the ammeter into the circuit. Switch on and note down the readingof the ammeter. Switch off.

RESULTS TABLE

VOLTMETER (VOLTS AMMETER (mA

Question to be answered to show understanding of the practical task.

Calculate the total resistance of the circuit and the supply current (is) with supplyvoltage at 11 V. The calculated current will be, within the limits of accuracy, thevalue measured on the meter.

--------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 5

THE WHEATSTONE BRIDGE

1. Connect the circuit as shown with the switch in the open position.

2. After the instructor has checked the circuit, set the ammeter at its highestrange. Close the switch.

3. Adjust the decade box until the ammeter reads as near zero as possible onthe lowest range. Note the value of the decade box. Switch off.

4. Calculate the value of Rx using the formula5.

5. Check your answer by measuring Rx on an ohmmeter.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 6

A.C. AND RMS VALUES

1. Connect a 100Ω resistor across 6.3 V RMS supply, as shown.

2. Connect an oscilloscope across the resistor and measure the peak to peakvalue.

3.

4. Connect a dvm set to measure A.C. voltage across the resistor. This showsthat, within limits, the device is calibrated in RMS.

5. Connect an ammeter, which must be set to measure A.C. current, in the

circuit. It should read V RMS / 100, to show it is also calibrated in RMS.

6. Using the time basis scale, show the supply frequency is 50Hz. Rememberthe frequency = 1/2 period.


Why is it not possible to display the workshop socket A.C. waveform on theoscilloscope?

--------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 7

D.C. AND THE CAPACITOR

1. Connect the circuit as shown in the diagram.

2. After the instructor has checked the circuit, switch on the supply. Notethe reading on the DVM every 10 seconds as the capacitor charges.When the DVM is steady, switch-off the supply. Discharge thecapacitor by switching the DVM to the D.C. ampere range.

3. Plot the results obtained on a graph and estimate the RC time of thecircuit (time to reach 6.32V).

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





RESULTS TABLE

TIME (S) DVM (V)

0

10

20

30

40

50

60

70

80

90

100

110

120

CALCULATIONS

Estimated RC time = _______________ secs

Calculated RC time = _______________ secs

QUESTION

Why are the estimated and calculated RC times different?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 8

THE INDUCTOR AND A.C.

1 . Connect the circuit, as shown, with the function generator set at 100Hz with a 1 V output. Write down the reading indicated on the mAmeter.

. Repeat step (1) with a function generator output of 1V for frequenciesof 200, 400, 800, 1000, 1200 and 1400 Hz. Note the reading of themA meter each time.

3. Work out the reactance of the coil at each frequency (divide 1V by mAreading).

4. Plot a graph of reactance against frequency.

5. The graph will show that inductive reactance increases linearly (in astraight line) with frequency.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





RESULTS TABLE

Supply voltage constant at 1 V.


(1) Calculate the reactance of the inductor at 1000 Hz.

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

(2) Why is it different from the measured value?

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 9

THE CAPACITOR AND A.C.

1. Connect the circuit as shown, with the function generator set at 100Hz with a 1 V output. Write down the reading indicated on the mAmeter.

2. Repeat step (1) with a function generator output of 1V for frequenciesof 200, 400, 800, 1000, 1200 and 1400 Hz. Note the reading of themA m meter each time.

3. Work out the reactance of the capacitor at each frequency (divide 1 Vby mA reading).

4. Plot a graph of reactance against frequency.

5. The graph will show that capacitive reactance falls exponentially withfrequency.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





Supply voltage constant at 1 V.


(1) Calculate the reactance of the capacitor at 1000 Hz.

--------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------

(2) Why is it different from the measured value?

--------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 10

A.C. CURRENT AND VOLTAGE IN AN INDUCTANCE

1. Connect the circuit as shown. Connect the earth leads of the oscilloscope(OSC) to the LOW side of the function generator.

2. Adjust the waveforms to approximately the same size and sketch thewaveforms shown on the oscillator.

3. The waveforms should, show approximately a 90° phase shift between the

voltage across the inductor and the current (voltage across the 20Ωresistor)

through the inductor.


Does the voltage lead the current or the current lead the voltage?

-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 11

A.C. CURRENT AND VOLTAGE IN A CAPACITANCE

1. Connect the circuit as shown. Connect the earth leads of the oscilloscope(OSC), to the low side of the function generator.

2. Adjust the waveforms to approximately the same size. Sketch thewaveforms displayed.

3. The waveforms should show approximately a 90° phase shift between the

voltage across the capacitor and the current (voltage across the 20Ω resistor) through the capacitor.


1 Does the voltage lead the current or the current lead the voltage?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 12

A.C. AND THE INDUCTOR / CAPACITOR RESISTIVE CIRCUIT

INTRODUCTION

The previous two tasks (10 and 11) showed the phase shift between thecurrent and voltage waveform when a capacitor or inductor is supplied with A.C. This task will show how the phase shift between the current and thevoltage can be adjusted. This is done using an inductor / capacitor with aresistor in a series circuit.

1 . Connect the circuit as shown. Sketch the two waveforms shown onthe oscilloscope.

2. Change the frequency to 500 Hz. Sketch the waveforms.

3. Change the frequency to 2000 Hz. Sketch the waveforms.

4. Replace the 100 mH inductor with a 0.1µF capacitor.

5. Repeat steps (1) through (3) and sketch the waveforms.

Questions to be answered to show understanding Of the practical task.

(1) Work out the phase shift at the various frequencies from the sketchesyou have made.

-----------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------

(2) Do these sketches show that the inductive reactance goes up with frequencyand the capacitive reactance goes down with frequency?

-----------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------. M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 13

RESONANCE

SERIES

1. Connect the circuit as shown.

2. Set the function generator to 200 Hz and note the reading on theDVM

3. Repeat step (2) for frequencies of 400, 600, 800, 1000, 1200, 1400.1800, 2000 and 2200 Hz.

4. Adjust the frequency on the function generator to obtain the largestreading on the DMV. Note the frequency.

5. Draw a graph of DVM reading against frequency.

6. The graph should show the circuit resonates. It. has a maximumvoltage (current) at one frequency.


----------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------

(2) Does your calculation agree with the result obtained from step (4) ?

----------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------- M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





PARALLEL

1. Connect the circuit as shown.

2. Set the function generator to 200 Hz. Note this reading on the DVMI.

3. Repeat step (2) for frequencies of 400, 600, 800, 1000, 1200, 1400.1800, 2000 and 2200 Hz.

4. Adjust the frequency on the function generator to obtain the smallestreading on the DMV. Note the frequency.

5. Draw a graph of the DVM reading against the frequency.

6. The graph should show the circuit resonates. It has a minimumvoltage (current) at one frequency.


------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------

(2) Does your calculation agree with the result obtained from step (3) ?

------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





RESISTANCE COLOUR CODES

Method 1

The diagram shows a colour coded resistor. The colour code is there toshow you the resistance of the resistor. Reading from left to right, the firstand seconds bands indicate a number, (eg. if the first colour band is 4 andthe second colour band is 7 then the number is 47). The third band is themultiplier in power form, (eg. 10

3) . The fourth band indicates the tolerance of

the resistor (eg. ± 5%). The numbers to match the colours are internationallyfixed and are given below.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





Example 1

GREEN

The example has the bands red, violet, green and gold. This means

27 x 100 000 (105) = 2.7 MΩ

Tolerance ± 5%

Example 2

The example has the bands black, green, gold and red. This means

05 x 0. 1 = 0. 5Ω

Tolerance ± 2%

Example 3

The example has the bands red, black, black and brown. This means

20 x 1 = 20.Ω

Tolerance ± 1 %

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





Method 2

The newer types of resistor have the value and tolerance printed on them. These

use letters to show the powers.

R = 1

K = 1000

M = 1 000 000

Examples

100 R = 100 Ω

1R1 = 1.1Ω

1 K5 = 1 500Ω

4M7 = 4 700 000Ω

This method of numbering resistors is now used on circuit diagrams and incatalogues when ordering resistors.

Note: Various colour codes for capacitors have been devised. However none ofthese are widely accepted so they are not worth learning.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





Tolerance:

This is the range over which a component is allowed to vary from its stated value.

The closer the tolerance- the more accurate the component. However, the closerthe tolerance the higher the cost. Electrical/electronic circuits are designed so thatclose tolerance components are only used when it is necessary for correctoperation.

Example

Find the acceptable range of values for a 1 K resistor with a tolerance of ± 5%.

5% of 1 000 = 50Ω

Acceptable range will be 1 000 ± 50Ω

or 950 Ω to 1 050Ω

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





Power Rating.

When an electric current is passed through a resistor, energy is dissipated (used) in

the form of heat. So, resistors are made according to how much heat (power) theycan take without burning out. This is called the power rating. The power -rating of aresistor is not usually printed on the resistor. The manufacturer's catalogue will tellyou the maximum power it can handle. The construction of resistors depends ontheir power rating. There are two basic kinds.

(1) Film Resistors

Figure PT-1 Film Resistor

Figure PT-1 shows a film resistor used in electronics. It is made by putting a thincoating (a film) of a carbon or metal compound onto a ceramic cylinder. Theresistivity of the coating compound is varied to give the necessary resistance value.The resistance can be made more accurate by cutting grooves in the film. Thegrooves change. the area and thus the resistance. The connections to the resistorare made by brass or nickel caps and copper connecting leads. The device iscoated with a plastic insulator and painted with the colour code. These resistors are

made in various values from about I Ω- to 10MΩ with a power rating to about 2W.

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s





(2) Wire Wound

These resistors are made for high power applications. An instrument technician will

only see these types in power amplifiers driving field devices (e.g. relays, solenoidvalves, etc.) however, they are often used in electrical work.

Figure PT-2 Wire Wound Resistor

Figure PT-2 shows a wire wound resistor. It consists of a ceramic cylinder with aresistance wire wound around it. The resistance value depends on the resistivity ofthe wire and the number of turns. These resistors can be very accurate. They areused as standard resistors. The insulation on the device depends on what thedevice will be used for. Very high power resistors which need to dissipate kilowattsusually have no insulation. They lose the heat by radiating it outwards like the sun.

Electronic power resistors are usually insulated with what is called 'vitreousenamel". This provides good insulation with good heat radiation properties. The wirewound resistor usually has its resistance value and its tolerance written on the

device (no colour code). Wire wound resistors are only produced in the lowerresistance ranges with a maximum value of about 100kΩ. The power ratingsproduced for electronics vary from about 2.5W to 50W. However, some electricalsystems may use resistors with power ratings of many kilowatts.

Note: The latest type of resistors come in what arecalled "chips". These arefilm resistors. They are constructed on a ceramic chip. There areconnecting pads on the bottom so it can be surface mounted on a printedcircuit board. The "chips" come from the factory stuck on a tape. They areremoved one at a time when they are needed. Figure PT-3 shows a typicalchip resistor.

Figure PT-3 Chip Resistor

M o

d u

l e

N o .

4 :

I n d u s

t r i a l e

l e c

t r o n i c

s 1

U n

i t N o .

8 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 5




July 1999- Rev.0

Page 1/13



UNIT 1 BASIC SEMICONDUCTOR THEORY

UNIT 2 DIODE APPLICATION

UNIT 3 THE CONTROLLED DIODE

UNIT 4 TRANSISTOR S


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 2/13


TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 BASIC ATOMIC THEORY 4

1.2.1 Electrical Conduction 6

1.3 THE INTRINSIC SEMICONDUCTOR 7

1.3.1 Doping an Intrinsic Semiconductor 8

1.3.2 The PN Junction 10

1.3.3 The PN Junction Diode 11

1.3.4 Diode Symbols 12

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 3/13




• Explain an electric current as a movement of electrons or holes.

• Explain the difference between a conductor, insulator and semiconductor byelectron shell theory.

• Explain the terms 'P' type and 'N' type material.

• Describe the action of a PN junction.

• With the aid of a sketch explain the action of a PN junction diode.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 5/13


as H20'



July 1999- Rev.0

Page 6/13


The electrical properties of an element depend on how many electrons are in theoutside shell. Good conductors like copper only have 1 electron in the outside shell.

Good insulators like neon have a full outside shell (8 electrons). Semiconductorsare half-full; eg, silicon. Elements are classified according to the number ofelectrons in the outside shell from group 1 (good conductors) to group 8 (goodinsulators). Group 3, 4 and 5 materials are used to make semiconductor devices inuse today, e.g. diode, transistor, integrated circuit etc.(see Figure 1-2)

• Group 1 example Lithium

One electron in the outside shell

• Group 4 example Silicon

Four electrons in the outside Shell

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 7/13


• Group 8 example Neon

Eight electrons in the outside shell

Figure 1-2 Atomic Shell Structure examples

1.2.1 Electrical Conduction

Figure 1-3 Simple Electrical Conduction

Figure 1-3 shows a few atoms in a conductor. Each atom has a single (free)electron in the outside shell. When an EMF is applied, the free electron (which hasa negative charge) is pulled towards the positive charge. The 'hole' left by theelectron is filled by the next moving electron. So, the hole (the positive charge)appears to move to the negative. The electron flow of an electric current is fromnegative to positive. Hole flow is from positive to negative. It is hole flow that is usedto show the direction of an electric current, (conventional flow).

Note : The charge of an electron is very small. A current of 1 Amp means that

1.6 x 10

19

electrons are moving per second.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 8/13


1.3 THE INTRINSIC SEMICONDUCTOR

The intrinsic semiconductor is a group 4 material with 4 electrons in the outsideshell. This means there are four (4) empty places in the outside shell into which anelectron can move. The most common intrinsic semiconductors are silicon andgermanium. They are produced as crystals. Crystals are an extremely pure form inwhich the atoms have a regular pattern (see Figure 1-4).

Figure 1-4 Arrangement of Atoms in a Crystal

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 9/13


The atoms hold together as a solid, by sharing the electrons between them to keepthe outside shell full some of the time. arrangement in which atoms share electrons

is called a covalent bond. A simple diagram of this is shown in Figure 1-5.

Figure 1-5 Covalent Bonding

Note : A good quality crystal has less than 1 part in 10,000,000,000 impurities.

1.3.1 Doping an Intrinsic Semiconductor

Doping an intrinsic semiconductor is the trick which makes all semiconductordevices work. There are only two types of doping that can be done.

N Type

A small amount of a group 5 material; eg, arsenic, which has 5 electrons in its outershell, is added to an intrinsic semiconductor. This causes the shared area around acovalent bond to have a 'spare' electron which is free to move; 4 from silicon 5 fromarsenic = 9 electrons. There is one spare electron because 8 is a full shell.

Figure 1-6 shows the action of an N type material which has free electrons to giveaway: doNate.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 10/13


Figure 1-6 ‘N’ Type Material

P Type

A small quantity of a group 3 material, eg, aluminium, which has 3 electrons in theouter shell, is added to an intrinsic semiconductor. This causes the shared areaaround a covalent bond to be one electron short. There are 4 electrons from siliconand 3 from aluminium which makes 7 electrons in total. This is one short of a full

shell so a 'hole' is produced where an electron can go. The P type material will takein electrons, accePtor. Figure 1-7 shows the action of a 'P' type material.

Figure 1-7 'P' Type Material

Note: The doping rates are very small, about one part in a million. However,doping rates vary depending on the amount of excess holes or electronsrequired.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 11/13




July 1999- Rev.0

Page 12/13


1.3.2 The PN Junction

Figure 1-8 The PN Junction

Figure 1-8 shows what happens when a piece of 'P' type material and a piece of 'N'type material are joined together.

The excess holes from the P side and excess electrons from the side cross thebarrier and cancel each other out. The 'P' area gain electrons and goes NEGATIVE,the 'N' area gains holes and goes POSITIVE. A CONTACT POTENTIAL is formed.The electric field which it produces stops any more hole-electron connections. The

area where these holes and electrons cancel each other is called the DEPLETIONLAYER.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 13/13


1.3.3 The PN Junction Diode

Figure 1-9 The PN Junction Diode

Figure 1-9 shows what happens when an external voltage is applied to a PNJunction. If the 'N' region is made positive to the 'P' region the depletion layer gets

stronger and no current flows. If the 'P' region is made positive to the 'N' region, thecontact potential and depletion layer are broken down and current will flow. The PN junction acts like a non-return valve. It allows current to flow in one direction only.Therefore, it is a diode. The current depends on the size of the voltage applied M

o d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 14/13


Note : The current will only flow in the forward direction after the contactpotential (barrier voltages) has been overcome. This is about 0.7v withsilicon diodes and about 0.2v with germanium diodes. If enough voltage

is applied in the reverse direction, the diode will break down and highcurrent will flow. The amount of voltage needed to do this is called theZENER breakdown voltage.

Figure 1-10 Diode Symbols

Figure 1 -10 shows the common symbols for a diode. Figures (a) and (b) show thesymbol used on an electronic diagram. The 'P' region is called the 'ANODE' and the

'N' region the "CATHODE'. Forward current flow is from anode to cathode. Figures(c) and (d) show the markings on the diode itself. Two examples of industrialsemiconductor diodes are shown below.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y



July 1999- Rev.0

Page 15/13


STUD MOUNTING

WIRE CONNECTIONS

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

1 -

B a s

i c s e m

i c o n

d u c

t o r

t h e o r y









UNIT 4 TRANSISTOR S


M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 SYMBOLS 4

3.3 CHARACTERISTICS 5

3.3.1 Forward Characteristics 6

3.3.2 Reverse Characteristics 7

3.4 PARAMETERS 8

3.5 IDENTIFICATION 9

3.6 TESTING DIODES 11

3.7 APPLICATIONS 13

3.8 LIGHT-EMITTING DIODES 15

3.9 REVIEW 17






The trainee will be able to:

• Recognise the common diode symbols

• Explain the meaning of

∗ Forward bias

∗ Reverse bias

∗ Anode

∗ Cathode

∗ Reverse (breakdown) voltage

∗ Forward voltage/current

∗ LED

∗ Photodiode

• Explain how to test a diode

• Briefly explain how diodes can be identified

• Describe one application for a diode (or an LED)

M o

d u

l e N o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





3.1 INTRODUCTION

A diode is a semiconductor device. It is usually made of Silicon (Si) or Germanium(Ge).

It has two terminal connections and, within voltage limits, conducts current only inone direction. It does the same job as a non-return valve. It is this characteristicwhich is important in electronics. Diodes are used to convert Alternating Current(AC) to Direct Current (DC). Direct Current is used in all electronic equipment.

The connections of a diode are called the ANODE and the CATHODE (see figure3.1). If the diode is FORWARD BIASED, the anode is connected to the positivevoltage and the cathode to the negative voltage. When the diode is forward biased,current flows through it. When the diode is REVERSED BIASED, only a very smallamount of current (leakage current) flows through it.

Figure 3-1 Symbol of Diode

Diodes allow current to flow only in one direction. It is this characteristic which isvery useful in electronics. Diodes are used to convert Alternating Current (AC) toDirect Current (DC). Direct Current is used for all electronic equipment. You willlearn about this when you study Rectifiers in Unit 4.

3.2 SYMBOLS

The general symbols for diodes are:

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





Figure 3-2 Symbols for Diodes

Some symbols also show the polarity of the diode (see figures 3.3 and 3.4).

Figure 3-3 Polarity of Diodes - Polarity shown by symbol

Figure 3-4 Polarity of Diodes - Polarity shown by line

3.3 CHARACTERISTICS

When a diode is connected to a supply with a positive anode and negative cathodepolarity, the diode is FORWARD BIASED.

M o

d u

l e N o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





When a diode is connected to a supply with a negative anode and positive cathodepolarity, the diode is REVERSE BIASED.

When the diode is Forward Biased, it conducts current. When the diode is ReverseBiased, it does not conduct much current.

Each of these two conditions has a different characteristic (see figure 3.5).

Figure 3-5 Characteristics of Forward and Reverse Biased Diodes

In figure 3.5, note that the current is shown in mA and µ A and that the forward

voltage is positive and reverse voltage is negative. Note also that the forwardvoltage is shown in tenths but the reverse voltage is shown in tens.

In figure 3.5 in FORWARD bias, the current through a Silicon diode begins to flowwhen the voltage reaches about 0.6V. In REVERSE bias, the current through theSilicon diode begins to flow when the voltage reaches about -50V. What are the twolimits for a Germanium diode?

3.3.1 Forward Characteristics

Figure 3.5 shows that Silicon diodes and Germanium Diodes have differentcharacteristics. The Silicon diode has a higher "turn-on" voltage and a higher"breakdown" voltage. The "turn-on" voltage is the voltage at which the diode beginsto work. The "breakdown" voltage is the voltage at which the diode cannot control

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i

c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





the current.





The Silicon diode has a higher FORWARD VOLTAGE DROP than the Germaniumdiode (see figure 3.6). In figure 3.6 the Silicon diode is shown with a FORWARD

VOLTAGE DROP from about 0.6V. What is the FORWARD VOLTAGE DROP ofthe Germanium diode shown in figure 3.6?

Figure 3.6 Forward Characteristics

There are many different types of diode. Some diodes break when only a fewmilliamperes (mA) of current flow through them. Other diodes break when over 100amperes of current flows through them.

3.3.2 Reverse Characteristics

In theory, no current flows when the diode is reverse biased. In practice, however,some LEAKAGE current does flow.

The Germanium diode has a larger leakage current at lower voltages than the

Silicon diode.

At some values of reverse voltage the current suddenly increases very quickly. Thisis called the REVERSE BREAKDOWN VOLTAGE. Voltage at this level will destroythe diode. So it must be controlled by a resistor connected in series (see figure 3.7).

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





Figure 3-7 Reverse Characteristics

The leakage current of diodes increases when the temperature rises. The leakagecurrent of Germanium diodes increases faster than Silicon diodes.

3.4 PARAMETERS

Diode manufactures give the following ratings, or information, about their diodes:

V-f Forward Voltage for a particular forward current (eg up to 1.5@ 5A for a silicon diode but the value will usually be less than1 V for most diodes) - or the voltage in a forward biasdirection - at which the diode begins to work.

I-f the Forward Current at which a diode begins to work.

V-rrm the Repetitive Reverse Maximum Voltage (sometimesreferred to as PRV - Peak Reverse Voltage - or PIV - PeakInverse Voltage). The amount of voltage a diode canwithstand in a reverse bias direction without breaking down.

When choosing a diode, you should consider:

• how much FORWARD CURRENT it will carry.(or at what voltage it will begin towork).

• how much REVERSE VOLTAGE it will tolerate (or at what voltage it will breakdown).

• whether it is made of Silicon or Germanium (remember that they have differentcharacteristics).

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





3.5 IDENTIFICATION

There are many different types, sizes, styles and ratings for diodes (see figure 3.8,

3.9 and 3.10). The diodes therefore have to be identified so that we know what theycan do.

Figure 3-8 Diode Case Styles


M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





There are two numbering systems for diodes. The AMERICAN system starts with a1 N. This means that the device has one PN junction. For example, a 1 N4004 is aSilicon diode with a voltage rating of 400V. A 1 N4020 is a Zener diode made of

Silicon with a voltage rating of 12V and which can handle 5W. A 1 N2326 diode ismade of Germanium with a rating of 1 V and 2mA. The numbers after 1 N arereference numbers.

The EUROPEAN Pro-Electron system starts with two letters. The first letters are Aor B. The second letters are Y or Z.

A = Germanium (a detection or switching diode)

B = Silicon (a variance capacitance diode)

Y = a rectifier diode

Z = a voltage reference diode (or a transient suppresser diode)

For example, a BY200 is a type of Silicon Rectifier diode. The numbers after thetwo letters are reference numbers.

Some diodes have ratings which say that they can handle only a few milliamperes.Other diodes can handle several hundred amperes (see figure 3.10).


M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





3.6 TESTING DIODES

Diodes can be tested with an ohmmeter:

• connect the ohmmeter across the diode

• look at the reading

• reverse the ohmmeter leads

• look at the reading

If the readings are exactly the same, the diode is probably not working. Can youexplain why? Remember that a diode works like a one-way valve.

The ohmmeter test is about 98% accurate. It is not 100% accurate because thediode could be overheating when the circuit is operating.

Diodes can also be tested with analogue and digital voltmeters.

Using a DIGITAL voltmeter (see figure 3.11), set it to the DIODE CHECK position.Note that the RED lead is the POSITIVE lead and the BLACK lead is theNEGATIVE lead.

The digital voltmeter uses a constant current to check resistance. On the resistancerange, the voltage would not be enough to "turn on" the diode since it is less than

0.6V. On the DIODE CHECK range, the current is still constant but there is enoughvoltage for the diode to conduct. The reading is the forward voltage drop of thediode. This reading is useful to find diodes with similar V-fs.

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





Figure 3-11 Using a Digital Voltmeter (DVM)

In figure 3.11 the lamp lights up when the supply is connected. When the current isreduced, the lamp becomes dimmer and the voltage falls. In figure 3.11 B when thediode is reversed, the lamp does not light up. Can you explain why?

Using an ANALOGUE voltmeter (or Multimeter), set it to the Ohms x 1 range. Inthis range, the BLACK lead is POSITIVE and the RED lead is NEGATIVE (seefigure 3.12).

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i

c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





Figure 3.12 Using an Analogue Multimeter

All the meters will show an OPEN CIRCUIT diode as an open circuit and a SHORTCIRCUIT diode as a short circuit.

Some diodes will show a resistance other than infinity when in REVERSE BIAS. ForGermanium diodes, this could be correct because Germanium diodes have moreleakage current than Silicon diodes. For Silicon diodes, a resistance other thaninfinity when in REVERSE BIAS probably means the diode is not working.

3.7 APPLICATIONS

The diode has many uses but two uses will be described here.

Look at figure 3.13. It is a circuit for a dimmer control for a lamp. The lamp is OFFwhen the switch is in the centre position. When the movable contact of the switchmeets the upper contact, the lamp is ON at FULL brightness because FULL voltageis supplied to it. 'When the movable contact meets the lower contact, the currentflows through the diode. The diode allows current to flow only one way. HALF of the AC Waveform is blocked during each cycle. So HALF of the voltage is supplied tothe lamp. So the lamp is ON - but at HALF brightness.

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





Figure 3.13 Lamp Dimmer Control

This is a dimmer control. The advantage of this type of control is that ordinarylamps can be used.

Look at figure 3.14. It is a circuit is for a dynamic brake for a small AC inductionmotor. AC induction motors can be braked by applying DIRECT CURRENT to theirstator windings. Remember that diodes allow current to flow only in one direction.The current becomes DIRECT CURRENT because it does not reverse direction.

Figure 3-14 Dynamic Braking Circuit for AC Induction Motor

The AC induction motor is OFF when the switch is in the centre position. When theswitch is in the MAINTAINED CONTACT position, the AC motor is ON. When theswitch is in the MOMENTARY CONTACT position, the current flows through thediode and the limiting resistor. This applies direct current to the stator winding andbrakes the motor. The resistor limits the amount of current to a safe value for thediode and the winding of the motor.

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





3.8 LIGHT-EMITTING DIODES

Light-emitting diodes (LEDs) give out light when current passes through them (see

figure 3.15).

Figure 3-15 - Light Emitting Diode

Photodiodes are turned on by light (see figure 3.16). They will not work withoutlight.

Figure 3-16 - Photodiode

Note the different direction of the arrows on the symbols.

LEDs and ordinary diodes are similar. They both allow current to flow in only onedirection but an LED needs a higher voltage to turn it on. An ordinary Silicon junction diode needs about 0.7V to turn it on. An LED needs about 1.7V to turn iton. An LED has a higher voltage drop than an ordinary junction diode. The highervoltage drop makes an LED difficult to test with some ohmmeters. The best way oftesting an LED is put it in a circuit and see if it works.

When it is in a circuit, an LED works with about 20mA (0.020A) or less of current.So when an LED is put in a 12V DC circuit, the current must be limited by resistorwhich is connected in series (see figure 3.17). Can you calculate the value for the

resistor? Use R=V ÷ I

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n

i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





Figure 3.17 Current Flow limited by Resistor

When an LED is connected in a circuit, it is important to know which lead is theanode and which lead is the cathode. Hold the LED with the leads towards you. Theplastic case has a flat side. The flat side should match the line on the diode symbol(see figure 3.18).

Figure 3-18 LED Polarity

LEDs are used for pilot lights and numerical and figure displays on electronicequipment. They are inexpensive. Unlike light bulbs, they do not have anyfilaments.

LEDs are used for seven segment displays. The seven segments can be lit indifferent combinations to make a variety of numbers and figures.

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i

c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n





3.9 REVIEW

• symbols for diodes, including LEDs.

• Forward Bias is when the diode is connected to supply so that, within limits,it conducts current.

• Reverse Bias is when the diode is connected to a supply so that, withinlimits, it does not conduct current.

• The anode and cathode are the diode connections.

• When the diode is Forward Biased the anode is connected to the positiveand the cathode to the negative voltage.

• Reverse Breakdown Voltage is the voltage at which the diode cannot controlthe current.

• Forward Voltage is the voltage at which the diode begins to work.

• LEDs are Light Emitting Diodes which give out light when current passesthrough them.

• Photodiodes are diodes which need light to work.

• Diodes can be tested to find out if they working by using ohmmeters ormultimeters connected across them.

M o

d u

l e N

o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c s

2

U n

i t N o .

2 -

D i o d e a p p

l i c a

t i o n



July 1999- Rev.0

Page 1/8






UNIT 4 TRANSISTORS


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e



July 1999- Rev.0

Page 2/8


TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 THE THYRISTOR (SCR) 4

3.2.1 A Typical SCR Control Circuit 5

3.2.2 The SCR in Industry 6

3.3 THE TRIAC 7

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e



July 1999- Rev.0

Page 3/8



The student will be able to -

• Describe the operation of a Thyristor (SCR).

• Draw and explain the operation of a typical variable D.C. supply using an SCR.

• Describe the operation of a TRIAC.

• Draw and explain the operation of a typical variable A.C. supply using a TRIAC.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e



July 1999- Rev.0

Page 4/8


3.1 INTRODUCTION

Units 1 and 2 described the diode and its applications. This unit will explain the

operation of diode devices which can produce a variable D.C. output from an A.C.supply, or a variable A.C. output from an A.C. supply.

3.2 THE THYRISTOR (SCR)

The thyristor or Silicon Controlled Rectifier (SCR) is a 3 PN Junction device. A veryenlarged view of the construction of an SCR is shown in Figure 3-1.

Figure 3-1 The Three Junction SCR

Operation

An AC supply is connected anode to cathode. This device will only conduct when avoltage is applied to the gate. With no voltage on the gate, the device will notconduct in either direction.

If a positive voltage of above 3V is applied to the gate a current will flow. The

forward bias of the bottom PN junction produces enough current carriers for apositive voltage on the anode to produce a current. This current will flow from anodeto cathode. However, a negative voltage on the anode produces no current floweven if the gate has a positive voltage. This means the device acts as a diode butits point of conduction is controlled by the voltage on the gate. The SCR cannot beswitched off once it is conducting. It will continue to conduct until the anode voltagefalls to zero.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e



July 1999- Rev.0

Page 5/8


3.2.1 A Typical SCR Control Circuit

Figure 3-2 Simple SCR Light Control Circuit

Figure 3-2 shows a simple SCR control circuit. It is used to control the brightness ofa lamp (the load).

Operation.

• The timing of the pulse onto the SCR gate is controlled by an RC timingcircuit and a UJT. The UJT (Uni-Junction Transistor) has only one junctionso it only conducts when the emitter is positive enough.

• The capacitor C charges through R on the positive half cycle to a pointwhere the M conducts. The high current passing through R, passes a pulseof voltage, via the diode, onto the SCR gate. When a voltage is applied tothe gate of the SCR it conducts and the bulb lights.

• The low resistance of the EMITTER-B1 junction shorts out the capacitor so itis ready for charging on the next positive halfcycle.

• The time at which the SCR conducts on the positive half-cycle depends onthe RC time. The RC time can be adjusted by R.

• If the RC time is long, the SCR will switch on later. If the SCR takes longerto switch on, the positive A.C. pulse across the lamp will be shorter. If the AC pulse is shorter, the lamp will get dimmer (less bright).

• The SCR is a diode so it only operates on positive half-cycles.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e



July 1999- Rev.0

Page 6/8


• The graph below shows the action of the circuit.

3.2.2 The SCR in Industry

The simple SCR control circuit has no practical use. It is only used to show SCRaction in a training workshop. An industrial SCR controller uses a complicatedswitching circuit. This is a separate electronic unit (card). Industrial SCRs are used

in different ways. You must use the manufacturer's manual to set them up. A typicalexample of SCR control is the large industrial battery charger. A typical circuit forthis is shown in Figure 3-3. The supply is three-phase with fullwave rectification.This gives six D.C. pulses per cycle which is more efficient (see Figure 3-3b).

Figure 3-3 The Basic Industrial Battery Charger

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e



July 1999- Rev.0

Page 7/8


Figure 3-3b

3.3 THE TRIAC

The triac is basically two SCRs back-to-back in one unit. It is used to control an A.C. wave. The symbol for a triac is

With a triac, the gate can be triggered by both negative and positive pulses (usuallypositive). Current will flow in both directions when either MT2 is positive to MT1 orMT1 is positive to MT2. The simple light control circuit (see Figure 3-4) can beadapted to use a triac which gives better control of light dimming as shown below.

Figure 3-4 Simple Light Control Circuit

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e



July 1999- Rev.0

Page 8/8


The dimming circuit works in the same way as before but the output voltage acrossthe lamp will be controlled A.C. The graph below shows the basic action.

Triacs are seldom used in industry as the distorted A.C. waveform causesunwanted electrical noise. This is difficult to filter out. However, they are used ininstrumentation as A.C. power switches. They are very good for switching devicessuch as valves, relays, turbine control valves, etc which are actuated by electricalsolenoids. Full AC voltage is applied when the triac is switched on, but there is novoltage when the triac is switched off.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

3 -

T h e c o n

t r o

l l e d d i o

d e









UNIT 4 TRANSISTORS


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





TABLE OF CONTENTS

Para Page


4.1 INTRODUCTION 4

4.2 THE BIPOLAR JUNCTION TRANSISTOR (BJT) 4

4.2.1 The BJT NPN Amplifier Circuit 6

4.2.2 The PNP BJT Transistor 7

4.2.3 The BJT PNP Transistor Amplifier 7

4.3 THE COMMON COLLECTOR (EMITTER FOLLOWER) AMPLIFIER 8

4.4 THE FIELD EFFECT TRANSISTOR (FET) 9

4.5 THE FET AMPLIFIER 10

4.6 THE METAL OXIDE SEMICONDUCTOR FIELD EFFECT

TRANSISTOR (MOSFET) 11

4.7 THE TRANSISTOR AS AN ELECTRONIC SWITCH 13

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r







• Explain with the aid of a diagram, the operation of a Bipolar Junction Transistor(BJT) amplifier.

• Explain with the aid of a diagram, the operation of a Field Effect Transistor (FET)amplifier.

• Explain with the aid of a diagram, the operation of a Metal Oxide SemiconductorField Effect Transistor (MOSFET) amplifier.

• Explain with the aid of a diagram, the operation of typical transistor switching

circuits.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.1 INTRODUCTION

The aim of this unit is to introduce the basic construction of three commontransistors in use: the Bipolar Junction Transistor (BJT), the Field Effect Transistor(FET) and the Metal Oxide Semiconductor Field Effect Transistor (MOSFET).

These devices use a D.C. power supply as an energy source to increase the levelof an alternating current signal to a usable level. No modern electronic devices(radio, stereo, television etc.) will work without transistors. This is because thesignals received from an aerial, tape or C.D. player are too small to see or hear.They must be amplified.

4.2 THE BIPOLAR JUNCTION TRANSISTOR (BJT)

Figure 4-1 (BJT) NPN Construction

Figure 4-1 shows an enlarged diagram of the construction of a BJT. It has two PNJunctions to make an NPN BJT. The three areas are called EMITTER, BASE andCOLLECTOR.

Operation

• The 'N' regions are more heavily doped than the 'P' region.

• The base is much thinner than the emitter and collector regions.

• The emitter-base junction is FORWARD BIASED. The- current which flowsis mainly ELECTRONS. These are the MAJORITY CURRENT CARRIERS.

• The base-collector junction is REVERSE BIASED. This means that theelectric field across the junction will pull the majority current carriers(electrons) into the collector region.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





The base current is very small because it is not heavily doped. So, there are fewholes for the electrons to combine with. Most of the electrons are pulled into the

collector.

The current passing into the collector, for a fixed collector voltage, is proportional tothe emitter-base bias.

The device amplifies because small changes in the base current produce largechanges in the collector current. The gain of a BJT is called HFE. HFE reflects thechange in the collector current compared to the change in the base current.

HFE =(GAIN) CHANGE IN BASE CURRENT

CHANGE IN COLLECTOR CURRENT

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.2.1 The BJT NPN Amplifier Circuit

Figure 4-2 The NPN BJT Amplifier

Figure 4-2 shows a typical NPN BJT small signal amplifier. The output signal is anamplified version of the input signal. The signal is amplified but it's not distorted.

Operation

• R1 and R2 set the bias voltage of the base-emitter junction so that the BJT isconducting at it's midpoint and the voltage at the collector (Vc) is half of+Vcc.

• The load resistor (RL) is added to develop a voltage output from the changes

in the collector current.

• C1 and C2 are added to block any D.C. levels which may affect the bias setby R1 and R2.

• If the input signal goes positive the forward bias of the base-emitter junctionis increased. This causes the collector current to go up so Vc will fall.

• If the input signal goes negative the forward bias of the baseemitter junctionwill fall. This causes the collector current to fall which means Vc will rise.

• The output signal is 180

° out of phase with the input signal (inverted) butamplified.

• This transistor is called a 'common emitter' amplifier because the emitter isconnected to both the input and the output.

• The symbol on an electrical diagram for an NPN BJT is

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.2.2 he PNP BJT Transistor

Figure 4-3 PNP BJT Construction

Figure 4-3 shows the basic construction of a PNP BJT. It works in exactly the sameway as an NPN BJT. However, the power supply are reversed and the majoritycurrent carriers are the holes (the spaces which attracts free electrons).

4.2.3 The BJT PNP Transistor Amplifier

Figure 4-4 PNP BJT Amplifier

Figure 4-4 shows a typical PNP BJT amplifier. The use of each component isexactly the same as for an NPN BJT but the DC supply is negative (-Vcc).

he symbol for a PNP Transistor is:

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.3 THE COMMON COLLECTOR (EMITTER FOLLOWER) AMPLIFIER

The normal small signal voltage amplifier is the one shown previously for both the

PNP and NPN. This circuit is not suitable for giving power to small resistance loads.The circuit used to provide power gain is called the common collector (emitterfollower) and shown in Figure 4-5.

Figure 4-5 Common Collector Amplifier

The load (RL) is connected in the emitter circuit of the BJT. 1 The voltage gain isless than one but the current gain and power gain. ~, high. This circuit will thusprovide the power to drive loads requiring high power, eg. stereo speakers, solenoidvalves, relays, etc. The output waveform is in phase with the input waveform.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.4 THE FIELD EFFECT TRANSISTOR (FET)

Figure 4-6 FET Construction

Figure 4-6 shows the construction of a field effect transistor (FET). It consists of apiece of 'N' material (the N channel) with P type material inset around the middle asshown. When there is no voltage on the 'P' region (gate), current flows from thedrain (D) to the source (S). If a negative voltage is applied to the gate a depletionlayer is created as shown. This makes the N channel smaller so less current flowsthrough it. The resistance of the 'N' channel goes up and the drain-source current(W goes down. If a big enough negative voltage is applied to the gate the depletionlayers close off the 'N' channel so that no current can pass through it. Then ID failsto zero. The gate voltage to do this is called the 'pinch off' voltage. It is possible to

change this device to a 'P channel` with inset 'N' type material. A 'P' channel FETworks the same way as an 'N' channel except the `pinch off' voltages are positive.

This gives a unit of conductance (1/Resistance). This unit of conductance is calledthe 'SIEMEN'.

FET Symbols

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.5 THE FET AMPLIFIER

Figure 4-7 The "N" Channel FET Amplifier

Figure 4-7 shows a typical N channel FET amplifier. The bias is set by R,. Thevoltage at Vs being ID R, positive. The voltage on the gate must be negative withrespect to the source.

The input signal developed across RG will move the gate voltage up and down. This

produces an inverted output signal similar to a BJT amplifier. The gain of an FETamplifier is small (around 10) compared with a BJT amplifier (around 100). But theinput resistance is very high unlike the BJT. However, the input resistance on anFET amplifier is much higher than on a BJT.

A P channel FET amplifier looks exactly the same as an N channel amplifier. Thebig difference is that VDD is negative.

Note : The capacitor Cl is used to short out any A.C. signals that would affect thebias developed across R,.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.6 THE METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR

(MOSFET)

There are two types of MOSFET; depletion (see Figure 4-8a) and enhanced (seeFigure 4-8b)

Figure 4-8 The MOSFET

The N-channel in the P substrate is insulated from the gate by silicon dioxide (Si02).When a voltage is applied across source and drain, a current will flow. The gate,insulator and N-channel act as a capacitor. When a voltage is applied to the gate acharge comes out of or goes into the N-channel. This increases or decreases thecurrent which flows from the drain to the source.

Any change in the gate voltage will produce a greater change in the drain circuit.This produces a gain similar to an ordinary FET. This device is usually made to behalf conducting when there is no gate voltage so an amplifier circuit does not needbiasing (see Figure 4-9).

Figure 4-9 Depletion MOSFET Amplifier

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





Depletion MOSFET symbol

Enhanced MOSFET

The enhanced type MOSFET has no inlaid N-channel. If there is no voltage on thegate there is no current flow between the drain and the source. A positive voltage

on the gate makes a current flow in the channel between the N+ regions. The sizeof this current depends on the size of the gate voltage. These devices are notnormally used as signal amplifiers because the biasing is complicated. However,they are very useful as electronic switches.

Enhanced MOSFET symbol

Note : P channel devices work in the same way as N channel devices except thegate voltage must be applied in the opposite direction. A negative gatevoltage increases the current flow from drain to source. This means a Pchannel MOSFET amplifier does not reverse the input signal. Input andoutput signals are in phase.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r





4.7 THE TRANSISTOR AS AN ELECTRONIC SWITCH

The previous sections explained the use of a transistor to amplify a small alternative

signal. This section deals with the use of a transistor as an electronic switch. Theonly transistors which are useful as switches are ones that are OFF normally andwill switch ON when a signal is applied.

The transistors discussed so far are :

BJT Normally off without bias

FET Normally on without bias

MOSFET (Depletion) Normally neither on or off.

MOSFET (Enhanced) Normally off.

This means the transistors used as switches are usually either the BJT or theMOSFET (enhanced). The circuit below (see Figure 4-10) shows the construction ofa typical BJT and MOSFET (enhanced) electronic switch.

Figure 4-10 Transistor Switches

Neither the BJT nor the MOSFET have any bias. A positive voltage applied to thebase or gate is sufficient to drive both devices into full conduction and to operatethe relay coil or solenoid valve. Remove the positive voltage and the deviceswitches OFF. A capacitor, C, is sometimes added, particularly to a BJT, to quickenthe switching action. The power MOSFET used as a switch is very popular today asit can be made to switch at least 200A as required.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

4 -

T r a n s i s

t o r



July 1999- Rev.0 Page 1 / 41






UNIT 4 TRANSISTORS


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 2 / 41


TABLE OF CONTENTS

Para Page

INTRODUCTION 3

PRACTICAL TASK 1 4

PRACTICAL TASK 2 7

PRACTICAL TASK 3 10

PRACTICAL TASK 4 18

PRACTICAL TASK 5 21

PRACTICAL TASK 6 24

PRACTICAL TASK 7 30

PRACTICAL TASK 8 34

PRACTICAL TASK 9 39


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 3 / 41


INTRODUCTION

The previous units (theory) have described the discrete (separate) componentswhich are used in electronics. These discrete components are only used ininstrumentation for simple tasks. Diodes for rectification. Transistors as outputdevices to drive 4-20 mA loops, relays, solenoids etc.

Most electronic tasks are done using Integrated Circuits (IC). These IC's provide theamplification, computing, switching, etc. of the electronic signals. The IC hasthousands of diodes, transistors etc. in one package using either BJT or MOSFETTECHNIQUES. The practical tasks given for this unit will enable you to learn theuse of discrete components and identify the circuits in an overall instrument circuitdiagram. The next unit will show you how to use IC's.

The connections to a component depend on the way it is made. The correctconnections to a device are given in data books which are held in the workshop.You must learn how to use these data books, with the assistance of the instructor.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 4 / 41


PRACTICAL TASK 1

THE PN JUNCTION DIODE

(1) Connect-up the circuit as shown in the diagram above.

(2) After the instructor has checked the circuit, set the variable DC supply togive 0.25V and note the mA reading.

(3) Repeat step (2) for 0.5V, 0.75V, 1 V, 1.5V and 2V.

(4) Reverse the positive and negative connections to the DC supply. Switch onthe power supply and note the mA reading for a 2V and 3V supply. Switchoff.

(5) Plot a graph of diode current (mA) against supply voltage.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 5 / 41


RESULTS TABLE

SUPPLY VOLTAGE (V) DIODE CURRENT (mA)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

2

-1 (Reversed connections)

-2 (Reversed connections)

Questions to be answered to show understanding of the task.

(1) IN 4001 is a silicon diode. From the graph estimate the forward bias required

to cancel the barrier (contact) potential.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

(2) Does your graph show that a diode is an electric check valve?

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 6 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 7 / 41


PRACTICAL TASK 2

THE ZENER DIODE

(1) Connect up the circuit as shown using the components supplied.

(2) After the instructor has checked the circuit, set the DC supply to 1 V andnote the mA reading.

(3) Repeat step (2) for a DC supply of 2V, 3V, 4V, 5V, 6V, 7V, 8V, 9V, 10Vnoting the mA reading each time. Switch off.

(4) Reverse the connections to the DC supply and the DMM. Switch on and

note the mA reading for a supply voltage of 0.5V, 1V, 1.5V and 2V.

(5) Draw a graph of zener diode current against supply voltage.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 8 / 41


RESULTS TABLE

REVERSE VOLTAGE REVERSE CURRENT

0

1

2

3

4

5

6

7

8

9

FORWARD VOLTAGE FORWARD CURRENT

0.5V

0.6V

0.7V

1V

2V


(1) Is the reverse zener breakdown voltage written on the zener correct?

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

(2) Does a zener diode act like an ordinary diode in the forward direction?

---------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 9 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 10 / 41


PRACTICAL TASK 3

THE DIODE AND RECTIFICATION

• HALF-WAVE RECTIFICATION

(1) Connect the circuit as shown using the components supplied.

(2) After the instructor has checked the circuit, switch on the AC supply andmeasure the peak voltage and period of the waveform shown on theoscilloscope (OSC).

(3) Sketch the waveform 'accurately on the graph paper supplied.


(1) What happens if the diode is reversed?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

(2) What is the RMS value of the AC supply?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 11 / 41


• FULL WAVE RECTIFIER


(2) After the instructor has checked the circuit, place the plug connected to theprimary side into the wall socket.

(3) Switch on. Measure the peak voltage of waveform seen on the oscilloscope(OSC).

(4) Sketch the oscilloscope waveform accurately on the graph paper provided.


(1) Does your sketch show full wave rectification?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

(2) What happens if the diodes are reversed?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 12 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 13 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 14 / 41


BRIDGE RECTIFIER


(2) After the instructor has checked the circuit, put the plug connected to theprimary side into the wall socket.

(3) Switch on the 240V - supply and measure the peak voltage shown on theoscilloscope.

(4) Accurately sketch the waveform shown on the oscilloscope on the graphpaper provided.


(1) Does the bridge rectifier circuit provide full wave rectification?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

(2) What happens if the diodes are reversed?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 15 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 16 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 17 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 18 / 41


PRACTICAL TASK 4

SMOOTHING CIRCUITS

THE RESERVOIR CAPACITOR


(2) After the instructor has checked the circuit, put the plug connected to theprimary side into the 240V wall socket.

(3) Switch on the 240V supply and carefully sketch the waveform seen on theoscilloscope. Switch off.

(4) Replace the 10 µF capacitor with a 100 µF capacitor.

(5) Switch on and carefully sketch the waveform seen on the oscilloscope onthe same sketch drawn during step (3). Switch off.

QUESTION to be answered to show understanding of the practical task.

What is the effect of changing the size of the reservoir capacitor?

------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 19 / 41


THE RESERVOIR CAPACITOR WITH FILTER CIRCUIT


(2) After the instructor has checked the circuit, put the plug connected to theprimary side into the 240V wall socket.

(3) Switch on the 240V supply and carefully sketch the waveform seen on theoscilloscope.

(4) Measure the size of the peak to peak ripple and the DC level using theoscilloscope.

(5) Find the frequency of the ripple using the oscilloscope. Switch off.


(1) Why is a 200Ω resistor used instead of an inductor?

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

2) Does the RC filter reduce the ripple?

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 20 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 21 / 41


PRACTICAL TASK 5

THE 3 LEG REGULATOR


(2) After the instructor has checked the circuit, put the plug from the primaryside into the wall socket.

(3) Switch on and adjust the variable resistor so that the ammeter reads 0. 1 A.Note down the reading on the voltmeter.

(4) Repeat step (3) for ammeters reading 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9and 1.0A. Note the voltmeter reading each time.

Do not exceed 1 A. Switch off

(5) Draw a graph of load current against output voltage.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 22 / 41


RESULTS TABLE

LOAD CURRENT (A) LOAD VOLTAGE (V)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


(1) How good is the regulation of the 3 leg regulator?

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

(2) Find the size of the ripple across the load, if load current is 0.5A.

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 23 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 24 / 41


PRACTICAL TASK 6

THE THYRISTOR (SCR)


(2) After the instructor has checked the circuit, switch on the A supply.

(3) Sketch the waveforms shown on the oscilloscope, for different settings ofthe variable resistor. Switch off.

(4) Place a 10µF capacitor (with the correct polarity) across the 5kΩ resistor.Switch on and prove to yourself that a variable DC level can be obtainedwhen the variable resistor is adjusted.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 25 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 26 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 27 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 28 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 29 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 30 / 41



Do your findings agree with the theory given?

------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 31 / 41


PRACTICAL TASK 7

THE TRIAC


(2) After the instructor has checked the circuit, switch on the A and DC supplies.

(3) Sketch the waveforms seen on the oscilloscope for various settings of the

variable resistor.

(4) Prove to yourself that the output is a variable AC waveform controlled by thetiming circuit.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 32 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 33 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 34 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 35 / 41


PRACTICAL TASK 8

THE BJT TRANSISTOR AMPLIFIER

Introduction

The BC 109 NPN BJT is not an accurate device. The gain (HFE) can vary over arange from about 100 to 400. The circuit shown is thus a compromise. Your friend's

results may be different from yours. However, if your circuit works then the resultsyou get are good.


(2) After the instructor has checked the circuit, switch on the DC supply (9v).

(3) With a voltmeter check that the collector / earth voltage is about +4.5V.Check the base / emitter voltage is about 0.7V.

(4) Using an oscilloscope display the output waveform on the screen. Adjust theinput signal to get the biggest undistorted signal (good sinewave). Measure

the peak to peak value of this output signal. Measure the peak to peak valueof the input signal.

(5) Switch off DC supply and AC sinewave generator. Change the BC 109 for aBC179 (the P type equipment of the BC109).

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 36 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 37 / 41


(6) Connect the DC supply with reversed connections. Switch on the DC supplyand AC generator.

(7) Repeat step (4). The results should be similar to the BC 109, the onlydifference is the reversed supply.

RESULTS TABLE

INPUT SIGNAL OUTPUT SIGNAL GAIN

BC 109

BC 179

QUESTION to be answered to show understanding of the practical task.

1) Is the output signal the same as an inverted amplified input signal.

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

2) What happens if the 1 OK resistor is shorted out?

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 38 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 39 / 41


M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 40 / 41


PRACTICAL TASK 9

THE COMMON COLLECTOR AMPLIFIER


(2) After the instructor has checked the circuit, switch on the DC supply

(3) With an input signal of 1 V p to p, find the p to p value of the output signal

on an oscilloscope. Prove to yourself that this circuit has a voltage gain ofless than one.

(4) Using both traces on the oscilloscope, show that the input and outputwaveforms are in phase.

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 41 / 41


PRACTICAL TASK 10

THE FET AMPLIFIER


(2) After the instructor has checked the circuit, switch on the D supply and thesignal generator.

(3) With an oscilloscope across the output, adjust the input A signal to obtainthe largest undistorted signal on the screen.

(4) Measure the input and output peak to peak signals. Find the gain of theamplifier.

RESULTS TABLE

INPUT SIGNAL OUTPUT SIGNAL GAIN

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0 Page 42 / 41



(1) Is the output signal an inverted version of the input?

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

(2) Which device gives the best gain; an FET or a BJT?

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

5 :

I n d u s

t r i a l e

l e c

t r o n i c

s 2

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 6







UNIT 1 DIGITAL MATHEMATICS

UNIT 2 INTRODUCTION TO DIGITAL SYSTEMS

UNIT 3 LOGIC GATES, FLIP-FLOPS, COUNTERS AND REGISTERS

UNIT 4 MEMORIES AND CLOCKS

UNIT 5 MULTIPLEXERS, DECODERS AND DISPLAYS

UNIT 6 DIGITAL / ANALOG & ANALOG / DIGITAL CONVERTERS

UNIT 7 THE COMPUTER

UNIT 8 INTRODUCTION TO DIGITAL TRANSMISSION


M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 BINARY NUMBERS 4

1.2.1 The Decimal System 4

1.2.2 The Binary System 5

1.2.3 Binary and Numbers Less Than One 7

1.3 OCTAL NUMBERS 10

1.4 HEXADECIMAL NUMBERS 11

1.5 BINARY CODED DECIMAL, OCTAL AND HEXADECIMAL 13

1.5.1 Binary Coded Decimal 13

1.5.2 Binary coded octal 14

1.5.3 Binary Coded Hexadecimal 14

1.6 BASIC BINARY ARITHMETIC 15

1.6.1 Addition 15

1.6.2 Binary Subtraction 16

1.7 BINARY MULTIPLICATION AND DIVISION 19

1.8 ALPHANUMERICAL CODES 20

1.9 CONCLUSION 22

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s







• Explain the binary system of numbers and convert from binary to decimal anddecimal to binary.

• Explain octal and hexadecimal number systems and convert these numbers todecimal. Convert decimals to octal and hexadecimal.

• Explain binary coded decimals (BCD), binary coded octal and binary codedhexadecimal.

• Carry out simple addition and subtraction of binary, octal and hexadecimal numbers

using one's and two's directed complements.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.1 INTRODUCTION

The aim of this unit is to introduce the mathematics required to understand digitalnumber systems which are now in common use throughout Companies.

1.2 BINARY NUMBERS

The binary system is a counting system used by computers. It's different from ournormal system of counting because it has a base of two. To understand the binarysystem it helps to start with our normal counting system and then compare it to thebinary system.

1.2.1 The Decimal System

Our normal counting system is the decimal system. In the decimal system there areten digits: 0,1,2,3,4,5,6,7,8,9. In this system, we write numbers as multiples of ten.So, the number 694 means 6 hundreds, 9 tens and 4 ones. We can show ones,tens, hundreds, thousands etc. as powers of ten:

Note: Any number to the power of zero is 1. So 10°= 1, 5° = 1 694° = 1 and 20° =1.

In the decimal system you can use the ten digits 0 to 9 in any column. The highestnumber in any column is 9. To write the next number you must use the next columnto the left. So, 9 means 9 ones. 10 means 1 ten and 0 ones. 19 means 1 ten and 9ones, 99 means 9 tens and 9 ones. 100 means 1 hundred, 0 tens and 0 ones. 999means 9 hundreds, 9 tens and 9 ones, and so on.

Figure 1-1

Try and write one thousand on the table (Figure 1 -1 ).

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.2.2 The Binary System

in _the binary system there are only two digits: 0 and 1. In this system we writenumbers as multiples of two. We can show ones, twos, fours, eights etc. as valuesof two.

Figure 1-2

Note: Any number to the power of zero is 1. So, 2° = 1.

In the binary system you can only use the two digits 0 or 1 in any column. The

highest number in any column is 1. So, 0 in the 2° column means 0 ones which iszero. 1 in the 2° means 1 one which is 1.1 in the 21 column and 0 in the 2° column

means 1 two and 0 ones which is 2. 1 and 1 means 1 two and 1 one which is 3. Towrite 4 you must move to the next column (2

2). 1, 0 and 0 means 1 four, 0 twos and

0 ones which is 4. 5 would be written as 1 four, 0 twos and 1 one; 6 is 1 four, 1 twoand 0 ones, 7 is 1 four, 1 two and 1 one and so on.

Try and write 8, 9, and 10 as binary numbers on the table.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





Modern electronic gates only have 2 states, on and off, (1 and 0). So, the binarysystem of numbers is the only one a modern computer understands.

The previous examples showed how a binary number can be translated to adecimal number. The next example shows a quick way of changing a-decimalnumber to a binary number.

The trick is to keep dividing the number by two. The binary number is the finalquotient, which is one (called the Most Significant Bit (MSB)). It is followed by all theremainders in reverse order.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.2.3 Binary and Numbers Less Than One

The previous paragraph explained how binary and decimal numbers are made forwhole numbers (e.g. 57, or 10110). This paragraph shows how to write numbersless than one.

The binary conversion to decimal is:

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





A further example is given to show the conversion of a binary number to decimal:

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





Converting a Decimal Number to Binary

You can convert a decimal number to a binary number by continually multiplying bytwo as follows:

The binary number is given by the carry column (from top to bottom).

The check is not exactly the same as the original number because the binarynumber was rounded down to 6 bits. The conversion is more exact if you use morebits. Your calculator will usually calculate and display to an accuracy of about 10bits. A good multimeter will calculate and display to 4 bits.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.3 OCTAL NUMBERS

The decimal system has a base of ten which means it uses ten digits. The binarysystem has base two. The octal system has base eight which means it uses eightdigits. The highest in any one column is 7.

The octal number 172 can be converted to the decimal system as follows:

To change a decimal number to an octal number you keep dividing the number by8. The octal number is the final quotient (MSB) followed by all the remainders.Converting the decimal number 247 into octal.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.4 HEXADECIMAL NUMBERS

The hexadecimal number system has base sixteen which means it uses sixteendigits. The highest number in any one column is 15. To avoid using two digits eg. 1and 5) in any one column, the hexadecimal system uses letters to represent thenumbers 10 to 15 as follows:

DECIMAL HEXADECIMAL

0 0

1 1

2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9

10 A

11 B

12 C

13 D

14 E

15 F

16 10

17 11

A typical hexadecimal number is written below :

The hexadecimal number 3AC

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





To change a decimal number to a hexadecimal number you keep dividing thenumber by 16. The hexadecimal number is the final quotient (MSB) followed by allthe remainders.

Converting the decimal number 247 into hexadecimal.

Note : Computers count in twos. However, large binary numbers can be verylong. For this reason large numbers are converted into octal andhexadecimal systems. These numbers systems are easy for computersbecause they are powers of two.

So, octal and hexadecimal numbers can be easily expressed in the binary systemusing 4 and 8 bit units (bytes). A good scientific calculator will change binary, octaland hexadecimal numbers into decimal and vice-versa. An instrument technician willneed a good calculator when programming Programmable Logic Control (PLC)systems at work.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.5 BINARY CODED DECIMAL, OCTAL AND HEXADECIMAL

This is a way of presenting decimal, octal and hexadecimal numbers for binary

processing in a computer. The table below shows the decimal (0-17), octal andhexadecimal numbers as they are changed to binary.

DECIMAL OCTAL HEXADECIMAL BINARY

0 0 0 0

1 1 1 1

2 2 2 10

3 3 3 11

4 4 4 100

5 5 5 101

6 6 6 1107 7 7 111

8 10 8 1000

9 11 9 1001

10 12 A 1010

11 13 B 1011

12 14 C 1100

13 15 D 1101

14 16 E 1110

15 17 F 1111

16 20 10 10000

17 21 11 10001

1.5.1 Binary Coded Decimal

This is used to change the digits in decimal numbers to binary numbers forcomputer calculations '(eg. putting decimal numbers into a calculator). The decimalnumber is binary coded as follows :

This code must be reversed by a BCD decoder before it can be shown as a digitalread-out (eg. on a multimeter).

The binary code for the decimal number is now processed in blocks of FOUR binaryBITS called a BYTE.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.5.2 Binary coded octal

This is used to change the digits in octal numbers to binary numbers for computer

calculations. The octal number is binary coded as follows.

The binary code for the octal number is now processed in units of 3 binary BITS

called a BYTE.

This code was popular when processing chips could only manage 4 bits at a time.Modern computer chips can use 32 bits at a time (one byte has 32 bits). This meansthat hexadecimal systems are mostly used today.

1.5.3 Binary Coded Hexadecimal

This is used to change a hexadecimal number (hex) to a binary number forcomputer calculations. The hexadecimal number is binary coded as follows :

The binary code for the hex number is now processed in blocks of 4 bits. These can

be grouped by a modern processor or chip into a BYTE of 32 bits.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.6 BASIC BINARY ARITHMETIC

1.6.1 Addition

In the decimal counting system, the highest number in any column is 9. When youadd numbers in the decimal system you "carry one". Carry one means adding oneto the next column on the left if the total is more than 9. So:

In the binary counting system, the highest number in a column is 1. When you addnumbers in the binary system you still "carry one". However, carry one in the binarysystem means adding one to the next column on the left if the total is more than 1 .

A further example is given below. In the left column there are 3 ones. The sum ofthe 3 ones is 1 carry 1. In the next column there are now four ones. The sum of four

ones is "zero" carry two (1 and 1 in the next column

1011100110110010

100001

1111 For every two ones a carry.each carry added to next column

1 1

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.6.2 Binary Subtraction

Binary Subtraction can be done in exactly the same way as with decimals using the

method of borrowing one from the next highest power (the next column to the left).However, the number which is borrowed from the next highest power is written as11 in the next column to the right:

As can be seen this method of subtraction is difficult in binary. it is not used in acomputer. The following two methods are used in computers.

ONE'S COMPLEMENT

One's complement is a method of subtraction which can be done easily in acomputer. The binary number to be subtracted is inverted (all the ones become zeroand all the zeros become ones). The two numbers are then added together. Thedigit on the left shows whether the final number is positive (1) or negative (0).

Invert the number to be subtracted (the bottom number) and add the two numbersas shown below.

+ 00100

The "1 " in the extra column on the left indicates a POSITIVE number and must beadded to obtain the answer:

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





Example 2: Subtract 11011 from 10111

Remember, invert the number to be subtracted and add the two numbers together:

The '0' in the first column means it is a NEGATIVE number. If the result is anegative number then the one's complement of the result (invert the result) providesthe answer.

11011 inverted = -00100

So, that 10111 - 11011 = -00100

Proof :

Note : ONE'S COMPLEMENT IS ONLY APPLIED TO THE NEGATIVE NUMBER.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





In the following example (example 2) the result is a negative number (it begins with1). In this case reverse two's complement is applied to the result.

The reverse two's complement of -1110 = - (0001 + 1) = -0010

Proof :

In the following example, both the numbers are negative. So, both numbers areinverted using two's compliment.

2's reverse of - 01100 =-(1 0011 + 1) = -10100

Proof :

Note :- TWO'S COMPLEMENT IS ONLY APPLIED TO THE NEGATIVE NUMBER.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.7 BINARY MULTIPLICATION AND DIVISION

Both multiplication and division are done in the same way as in decimals. The two

examples below show how this done. The computer does this process by eithercontinuous addition or subtraction and this need not be remembered.

Multiplication:

Division:

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





1.8 ALPHANUMERICAL CODES

The binary code for the computer is called the "Machine Code". This is the code the

computer (machine) understands. The previous section showed how to get thebinary code for numbers. However, a binary code must also be made to representletters. The standard computer keyboard is arranged in the same way as atypewriter; it has a "qwerty" keyboard. There is an international standard code which"assembles" both numbers and letters from the keyboard into the "Machine Code".This code is called "ASCII" (American standard code for information interchange). Itis an 8 bit code which provides 256 characters for upper and lower case alphabets,numbers, punctuation marks, symbols etc.

A few examples of this code are given in the table below. The code is given inhexadecimal for convenience. The machine code for the computer is in binarycoded Hex. The following examples are given as a reminder.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





Some examples of ASCII (8 Bit code)

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s





There are many other alphanumberic codes used by manufacturers. These codeswill have to be learnt during specialised training, e.g. using the TDC 3000 orFoxboro ]A keyboards. You have already learnt one of these codes when using the

Autodynamic simulator keyboard.

The best known example of a modern alphanumeric code is the "Bar Code" as usedon supermarket products. This code allows the price to be taken automatically andis used to keep control of stock.

Note: Setting the rules for a computer using a "machine code" or"alphanumeric code" would take a very long time. To make things gofaster a high level code (language) is used which does whole sentencesat one time. These high level languages are learnt by the systemsengineers. Then they programme the system to do what is wanted (e.g.PID control, Logic control etc.). Examples of these languages are

Fortran, Pascal, C, Unix, etc.

1.9 CONCLUSION

This unit has shown you the basics of computer mathematics. You have learned thebinary, octal and hexadecimal number systems and how to add up and subtract inbinary. A computer uses these methods and others to do basic arithmetic. How acomputer makes up a number for processing and transmission will be shown on amore advanced training course.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

1 -

D i g i t a l m a

t h e m a

t i c s











UNIT 6 DIGITAL/ANALOG & ANALOG/DIGITAL CONVERTERS

UNIT 7 THE COMPUTER



M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n

t o d i g i t a l s y s

t e m





TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 THE ANALOG SIGNAL 4

2.2.1 Analog Systems 4

2.3 THE DIGITAL SIGNAL 6

2.3.1 Digital Systems 8

2.4 ANALOG/DIGITAL COMPARISON 10

2.4.1 Analog 10

2.4.2 Digital 10

2.5 THE 4-20 mA ANALOG CONTROL LOOP 11

2.6 THE DIGITAL CONTROL LOOP 12

2.7 DIGITAL TRANSMISSION 13

2.8 EXAMPLES OF A DIGITAL TRANSMISSION SYSTEM 13

2.8.1 E.S.D Systems 13

2.8.2 Tank Farm Systems 14

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m







• Explain with the aid of a diagram an analog signal.

• Explain with the aid of a diagram a digital signal.

• Explain with the aid of a diagram an analog instrument loop.

• Explain with the aid of a diagram a digital instrument loop.

• Describe, in general terms, how a digital transmission system works.

• Use block diagrams to explain the use of digital transmission systems in the

petroleum industry, e.g. ESD systems and tank farm operations.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





2.1 INTRODUCTION

The aim of this unit is to describe the differences between analog and digital

systems. It explains the basics of digital transmission, and gives general examplesof how digital transmission is used in the petroleum industry.

2.2 THE ANALOG SIGNAL

Figure 2-1 Analog Signal (as shown on the oscilloscope)

Figure 2-1 shows a simple circuit which produces an analog signal. The variableresistor is placed across a supply. The slider (moveable arm) of the variable resistoris moved by the process variable. The output signal shown on the oscilloscope,changes continuously with time. The output signal depends on the position of the

variable resistor slider.

2.2.1 Analog Systems

Analog systems are still used because they are easier to make. The sensor itselfproduces an analog signal. The control valve needs an analog signal. So, it issimplest to use a (4-20 mA) analog signal for the loop. Also people must haveanalog systems in order to see and hear etc. That's why televisions, radios, andcassette players etc. must produce analog signals.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





However, the analog system needs a large bandwidth of frequencies when sendinga signal. This reduces the number of signals (television channels, etc.) that can besent along one cable. Analog systems are also very sensitive to noise and cannot

produce a good quality television picture or good quality sound over a radio orcassette player.

. Figure 2-2 shows how amplifiers are connected to make an Analog ProcessController.

Figure 2-2 Analog Process Controller

The error detector senses any difference between the set point (SP) and themeasured value (MV). It sends a signal to three amplifiers in parallel. Theproportional amplifier sets the gain of the system. The Integral reduces any offset tozero. The derivative speeds up the initial change in the system (particularly used forslow response loops). The responses of these three amplifiers are combined andconverted to a current signal. This signal adjusts the I/P converter which adjusts theposition of the control valve. The action of the three amplifiers is adjusted so that

the control valve responds as quickly as possible to changes in the loop, withminimum overshoot. The curve shows this effect using a set point change.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





The response time will be slow (minutes) on most control loops and can be hourson some temperatures loops. Each individuals loop has its own controller. On alarge refinery the control room is very large. There are hundreds of individual

control loops for the various physical properties being measured (e.g. pressure,temperature, pH, 02 content, etc.)

2.3 THE DIGITAL SIGNAL

Figure 2-3 Digital Signal

Figure 2-3 shows a simple circuit which produces a digital signal. The processvariable operates a switch which opens and closes the circuit. The output signal isalways the same level but comes as a series of pulses (digital) depending onwhether the switch is open or closed. The system has a fixed timing sequencewhich produces a series of "ONES" and ZEROS" to represent the process variable.

A typical example of a digital signal is shown in Figure 2-4.

Figure 2-4 A Digital Signal

The process variable timing sequence takes 1 6us There are 8 timing intervals of2us Each digit ("1") is 1.2~is long. The digital presentation of the process variable is

10111001 Each following 16~is will produce a similar 8 digit sequence whichreflects the value of the process variable.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





From previous units it has already been shown that the transistor (FET) is ideal as ahigh speed switch to provide either a maximum (on) or minimum (off) signal. By

manufacturing thousands of these FET switches on an integrated circuit the basicsof a digital computer is obtained. However, there are only two states for any oneswitch. The system is binary so it can only count in twos giving either a one or zerooutput. Each ONE or ZERO is called a "BIT" of information, a "BYTE" is the wordlength of the processing system, e.g. 8 bits or 16 bits taken at one time.

Note : Bit rates are an approximation for powers of 2, thus:

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





2.3.1 Digital Systems

Digital systems produce better quality signals than analog systems (e.g. a compactdisc player has better sound than a cassette player). The bandwidth is alsoreduced. There are at least 5 times as many channels on a television when the newdigital television signals are used. The picture is also much better. Unfortunately,new television sets are needed to process digital signals.

Digital systems are more complicated than analog systems. This is because theanalog signals from the sensor must be converted to digital signals using an analogto digital converter (A/D). Digital signals must be converted to analog for the controlvalve using a digital to analog converter (D/A). Both these devices will be explainedlater in the course.

Digital systems are slowly coming into the petroleum industry as they use less cableand cost less to install. The reduced bandwidth needed for each loop means thatmany signal loops can be sent from one area to another using one cable or radiolink.

The digital system of control is based on the micro-computer which operates inmicro-seconds. So, using digital techniques it is possible to control all the loopsfrom one place. This means that the operator can use a VDU to control the plantfrom one position. Therefore, there is no need for a control room with an individualindicator controller recorder for each loop.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





Figure 2-5 The Digital Controller

Figure 2-5 shows a typical layout of a control system using a microcomputer. It hasthe following components.

a) Signal Conditioning Cards (SCC): These take the analog signals from theinput transmitters etc. and put them into a form acceptable to the dataacquisition system (usually 1-5 volts). Typical signals are 4-20 mA, mV(thermo-couples), pulse trains (turbine meters) and resistance (RTD).

b) Data Acquisition System (DAS): This unit changes all input signals into adigital format which is acceptable to the microcomputer. It also switches the

loops for processing.

Note: Modern digital systems combine (a) and (b) in one unit.

c) Input Ports: These connect the digital input signals from the field to thecomputer.

d) Output Ports: These connect the computer to the control devices, e.g.relays, digital/analog converters for 4-20 mA signals, solenoid valves, etc.They also provide the signals for the VDU display.

e) The Keyboard: This lets the operator communicate with the computer. Using

a set program the operator can call up the required loop, display it andchange the PI and D configuration as required. This is usually done underengineering supervision.

(f) The Micro-Computer: This controls the system. Using a set program it willcheck each loop and adjust the control as required. It has a memory to storeeach loop's operating data so that it has a reference for each check. Eachcheck only takes micro-seconds so each loop can be checked everyhundred milli-seconds or so. The type of micro-computer used depends onthe system. The Foxboro !A is based on the Intel 80286 16 bitmicro-processor.

(g) Timer: This is an electronic clock which times the operation of the system.Each operation is in time with a clock pulse. In this way the micro-computeris synchronised with the information coming in and going out.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





2.4 ANALOG/DIGITAL COMPARISON

2.4.1 Analog

2.4.2 Digital

Analog technology is well known and has been in use for years. Most sensors usean analog system. So, for single loop and small system control the analog system ischeap and easy to service using standard equipment.

However, for larger systems, e.g. chemical plants, oil/gas production platforms etc.,The analog system is difficult and expensive to install. It needs a lot of wiring tocomplete all the loops. It also needs a large control room with many discrete

controllers/indicators/recorders which must be supervised by the operator on duty.

Analog signals are also very sensitive to noise. Noise degrades the signal andcannot be removed,

Digital control systems are only possible because of the development of theintegrated circuit. It is much more complicated to process information using a digitalsystem than an analog system. However, once they are installed, digital systemsare more reliable than analog systems. They are noise free so there is not muchinterference from atmospherics, etc.

A Distributed Control System (DCS) with modems and fibre optic cables addedneeds much less wiring. Also, it is cheaper to supervise the control room, if smartsensors are used which control between themselves without using the maincomputer.

Unfortunately, the introduction of digital control means that the instrumenttechnician has to improve his knowledge of electronics and learn a completely newmethod of control. That is the object of this training module.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





2.5 THE 4-20 mA ANALOG CONTROL LOOP

Figure 2-6 The 4-20 mA Analog Control Loop

Figure 2-6 shows a 4-20 mA analog loop using a microprocessor (µP) controller andVideo Display Unit (VDU).

The resistance of the transmitter changes as the process variable changes. Thevariable, analog current signal which is produced is passed through the input of theconditioning unit. This unit converts the analog signal to a digital signal so that the

µP controller can process the signal. The digital signal output from the j-LPcontroller is returned through the output unit. This converts the digital signal back toan analog current signal. The analog signal is converted to a pneumatic signal bythe I/P to position the valve.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





2.6 THE DIGITAL CONTROL LOOP

Figure 2-7 The Digital Control Loop

Figure 2-7 is a simplified diagram of the latest type of digital control. The transmitteritself converts the analog sensor signal to a digital signal. The input loop sends onlydigital signals. These do not need to go through a conditioner so they go directly tothe control processor. The output loop sends only digital signals. The valve

positioner uses a µP to set the correct position of the valve. The valve actuator isusually either electro/hydraulic or pneumatic in operation.

Note: There is a half-way system in use called "Smart". You have alreadyworked on these in the workshop. The. "Smart" system is basicallyanalog in operation. The digital signals placed on top of the analogsignal are used for calibration.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





2.7 DIGITAL TRANSMISSION

There are many methods of organising the digital pulses so that the microprocessorcontroller can understand the signal that is being sent. The method used is called a"protocol". Most manufacturers now use a protocol called "Hart", developed byRosemount. The "Smart" transmitters you have worked on use "Hart".Understanding "protocols" and fault finding digital transmission systems will belearnt on advanced courses later in your career.

2.8 EXAMPLES OF A DIGITAL TRANSMISSION SYSTEM

The following examples show in simple terms the use of digital transmissionsystems in the petroleum industry.

2.8. 1 E .S.D Systems

Figure 2-8 Digital ESD System

Figure 2-8 shows a typical digital control system used for ESD processing. Thelocal control unit has many field alarms connected to it. The controller in the localcontrol unit puts all the separate input signals into a timed sequence (multiplexed)digital stream. This means that all the input signals can be sent down one cable to

the control room. The control room µP de-multiplexes (separates) the digital stream

and shows the alarms separately on the alarm panel. This process of sending allthe alarm signals digitally down one cable saves kilometres of cable and reducesthe time it takes to install the system.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m





2.8.2 Tank Farm Systems

Figure 2-9 Tank Farm Systems

Figure 2-9 shows a popular tank farm management system for indicating tank levelsin a control room.

The level transmitters (e.g. ENTIS-ENRAF) process the level of each tank intodigital signals. The field communication unit combines these signals and sends a

multiplexed signal down one cable to the control room, The µP in the control roomde-multiplexes the signal and displays each level separately on the VDU.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

2 -

I n t r o

d u c

t i o n


t e m












UNIT 7 THE COMPUTER



M o d u l e


s 3

U n i t

N o . 3 - L o g i c g a t e s , F l i p - f

l o p s , C o u n t e r s a n d R e g i s t

e r s





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 LOGIC GATES 4

3.3 THE SR FLIP-FLOP 7

3.4 THE JK FLIP-FLOP 8

3.5 THE "D" FLIP-FLOP. 10

3.6 THE PRACTICAL JK FLIP-FLOP 11

3.7 COUNTERS 12

3.7.1 The Non-Synchronous Counter; (Ripple Counter) 12

3.7.2 The Synchronous Counter 14

3.7.3 The Decade Counter 15

3.7.4 Counter Chips 16

3.8 THE REGISTER (ACCUMULATOR) 17

M o d u l e


s 3

U n i t



e r s







1 Draw the basic symbols for logic gates to include multiple units.

2) Draw a typical SR flip-flop.

3) Make a truth table for an SR flip-flop.

4) Draw a JK flip-flop and make a truth table to show its operation.

5) Draw the following counters made from flip-flop's and explain how theycount.

• Ripple counter

• The synchronous counter

• Decade counter

7) Draw and explain the register.

8) Explain the meaning of SISO, SIPO, PISO and PIPO registers.

M o d u l e


s 3

U n i t



e r s





3.1 INTRODUCTION

The aim of. this unit is to review logic gates and the use of these gates to make thebuilding blocks for digital systems.

3.2 LOGIC GATES

The following diagrams are given as a review of the logic gates learnt in Unit 2Industrial Electronics 3. Extra symbols have been added to show the latest symbolswhich are an American (IEEE) and International (IEC) joint standard.

M o d u l e


s 3

U n i t



e r s





M o d u l e


s 3

U n i t



e r s





Note: The old symbol for a "NOT" function was a circle. The new IEEE/IECsymbols use the triangle to show a "NOT" function. It is possible for

symbols to have inverters shown on the input so that:

Most gates today come as multiple units and the new standard symbol for a 2 inputquad NAND gate (e.g. 7400) is drawn as follows (the old symbol is shown on theright so that you can compare the two).

M o d u l e


s 3

U n i t



e r s





3.3 THE SIR FLIP-FLOP

The SR (set-reset) flip-flop is the basic building block for most digital devices, (e.g.memories, registers, converters, etc.). It will keep either a "V' (high) or "0" (low) as acontinuous output. The output will not change unless the input is changed.

Figure 3-1 SR Flip - Flop Block Diagram

Figure 3-1 shows an SR flip-flop in block diagram form.

The SR flip-flop has two input connections; S and R. It also has two outputconnections; Q and Q1 (Q1 = not Q or opposite of Q). Normally there is a " 1 " on Sand “0" on R. The outputs are " 1 on Q and “0" on Q1. If the " 1 " on S is removednothing happens. If a " 1 " is now applied to "R" the flip-flop changes over. Thismeans that the Q output is "0" and Q1 output is " 1 ". If there is a " 1 " on both R andS the flip-flop may change its position or it may not. This is called the "undefined"position and is not allowed.

A simple truth table below is given to shows its operation.

M o d u l e


s 3

U n i t



e r s





3.4 THE JK FLIP-FLOP

The SR flip-flop as a chip is now obsolete and is little used today. The JK flip-flophas taken its place. The JK flip-flop has the advantage of having no "undefined"position. It can be connected as an SR flip-flop if required.

The JK flip-flop can be operated in two ways; synchronous or asynchronous. Thetwo words are often used in digital systems and you must learn what they mean.

Synchronous means the system runs like a clock. There are a fixed number ofpulses per second (e.g. 4M bit). The pulses from the clock and the changes in theinput both change the outputs. Asynchronous means the system runs without timinglike the SR flip-flop. You can only change the output by changing the input.

Figure 3-2 JK Flip-Flop Block Diagram

Figure 3-2 shows the JK flip-flop. The pulses from the clock can switch theflip-f lop. With a " 1 on the J terminal and a '0' on the K terminal, the outputs are Q =“1 " and Q1 = 0. If there is a “0” on the J terminal and a "'I " on the K terminal thenthe outputs reverse. If a " 1 " is applied to both J and K then the outputs follow theclock with the Q1 output out of phase with the Q output. This position is called a"toggle".

M o d u l e


s 3

U n i t



e r s





The truth table for a JK flip-flop is given together with the pulse diagram

The JK flip-flop has the advantage of having no "undefined" position. It can be usedas an SR flip-flip simply by not connecting the clock.

Note: The above flip-flops can be made using either "NAND" or "NOR" gates.The actual circuit need not be remembered as these devices aremanufactured as IC chips. You are not given information about how it ismade. An example is the CMOS 4027 dual JK flip-flop.

M o d u l e


s 3

U n i t



e r s





3.5 THE "D" FLIP-FLOP.

This is an adaptation of the JK flip-flop. It allows for the switching of one input only.It delays the passing of the input signal by one clock pulse. That's why it's called the"Delay" or M" flip-flop.

Figure 3-3 M" Flip-Flop Block Diagram

Figure 3-3 shows the block diagram for a "D" flip-flop. There is only one input. An"on chip" inverter reverses the D input signal to the K input.

The output at Q will be a "1' if D is "1' and "0" if "D" is zero. The output changes atthe end of the clock pulse so that a change in D is delayed by one clock pulse. "D"flip-flops are like JK flips-flops as they are manufactured in DIL packages, e.g.

CMOS 4013 dual D flip-flop.

M o d u l e


s 3

U n i t



e r s





3.6 THE PRACTICAL JK FLIP-FLOP

The manufactured JK flip-flop comes with extra connections; "preset" and "clear".

Set : Pre-set = 0: Clear = 1: therefore Q = 1

Reset: Pre-set = 1: Clear = 0: therefore Q = 0

Toggle: Pre-set = 1; Clear 1: therefore Q = ?

Note : Pre-set 0 and Clear 0 is not allowed.

The output Q depends on the data at J and K and the clock. It is the same as in aJK flip-flop.

JK flip-flops come in two types. Type 1 switches on the positive going edge of theclock pulse. Type 2 switches on the negative going edge of the pulse. The JKflip-flop described was of the negative edge type.

M o d u l e


s 3

U n i t



e r s





3.7 COUNTERS

These are integrated circuits. When they are connected to a data stream of bits,they count them.

3.7.1 The Non-Synchronous Counter; (Ripple Counter)

The simplest type of counter is called a RIPPLE COUNTER. The data passesthrough the device like waves hitting the sea shore. Figure 3- shows a typical ripplecounter using 4 JK flip-flops.

Figure 3-4 Typical Ripple Counter

Remember all the J and K inputs are at "1'. Each JK flip-flop gives an output signalas it receives a pulse from the clock terminal. The table below gives the count andthe waveform for each particular JK output.

M o d u l e


s 3

U n i t



e r s





A ripple counter is only used if speed is not important. This is because it may taketoo much time for the clock pulse to ripple through several stages. The time it takesfor the ripple to pass can be shortened by using a synchronous counter. In thissystem all the flip-flops are switched at the same time.

M o d u l e


s 3

U n i t



e r s





3.7.2 The Synchronous Counter

Figure 3-5 shows a typical synchronous counter. Note that the inputs J and K onflip-flop A are ONE and all other flip-flop X inputs are joined together and controlledby the AND gates X and Y. The waveforms of the 4 outputs are given below.

Figure 3-5 Synchronous Counter

Note: The output at QD comes after 16 input bits. Thus the circuit can be usedto divide things by 16. In the same way Qc will divide by 8, QB by 4 andQ A by 2.

M o d u l e


s 3

U n i t



e r s





3.7.3 The Decade Counter

The most popular type of decade counter (a device which counts in tens) usesflip-flops with a reset connection. If a ONE is removed from this connection theoutput goes to zero. An example of the use of this type of flip-flop is given in Figure3-6.

Figure 3-6 The Decade Counter

The counter works as follows:

All the J and K inputs are connected to the high " 1 " position (e.g. 5V). The data tobe counted is applied to the clock connection of flip-flop A.

M o d u l e


s 3

U n i t



e r s





3.7.4 Counter Chips

The previous pages have shown how individual JK flip-flops are connected to makecounters. There is no need to remember how this is done as they are manufacturedas IC chips. A typical example of a counter chip is the 7493 14 pin TTL 4 bit binarycounter. The pin connections are the same for every manufacturer. They are givenin standard electronic data books. Normally the data book shows the basic blockdiagram of how the chips are connected. It also shows how to connect them. Anexample is shown in Figure 3-7.

Figure 3-7 Pin Connections for a 7493 4 Bit Binary Counter

If pin 12 is connected to pin 1 it is a 4-stage ripple counter. R1 and R2 are re-setconnections. A " 1 " applied to both positions clears the counter. This can be turnedinto a decade counter by connecting pin 9 to pin 2, pin 11 to pin 3, and pin 12 to pin

1.

M o d u l e


s 3

U n i t



e r s





3.8 THE REGISTER (ACCUMULATOR)

A register (accumulator) is a temporary storage device for data coming into or out ofthe processor. It also stores data which is not completely processed. When it isconnected in the right way it can take this stored data and switch it to either aparallel or a serial output. It is the basic block for storing a digital number andmoving it about. Figure 3-8 shows a typical register using JK flip-flops.

Figure 3-8 Register

This unit will store a 4 bit binary number as follows.

At the start, the reset has cleared the register.

Q A = 0, QB = 0, QC = 01, QD = 0

Let us suppose that the number to be stored is 1101. This is fed into the data inputin the order that it reads from left to right. The register will then store the number asfollows.

M o d u l e


s 3

U n i t



e r s





If the clock is now stopped the accumulated number will stay in the register as longas the supply stays switched on. So, this unit can be a 4 bit memory circuit.

If the clock is started again then the data will leave the output (QD) in the order itwas entered.

This kind of register can be used to hold a number so it can be processed later. It isthen called an ACCUMULATOR. If the data is moved in and out it is called a SHIFTREGISTER.

The shift register shown moves the data in and out in serial form (one after theother). However, shift registers can be used to provide a parallel output (all the datacomes out at the same time). Thus the shift register can come in 4 different forms,depending on requirements, as follows.

M o d u l e


s 3

U n i t



e r s





1 ) SISO (Serial in-Serial out)

This is the method shown above. It acts as a short term storage device or adelay circuit. The data can only be accessed in the order in which it isstored. The first bit of data IN must be the first bit of data OUT.

2) SIPO (Serial in-Parallel out)

The information is stored as described above. However, when theinformation is accessed by the next clock pulse, all 4 bits of data come out ofthe outputs at the same time. It is used to change information from serial toparallel form.

SIPO Shift Register

3) PISO (Parallel in-Serial out)

This is the opposite of SIPO. After a clock pulse is applied, the next clockpulse will apply the 4 bits (byte) to all flip-flops simultaneously (at the sametime). The following 4 clock pulses will then read out the number in serialform.

M o d u l e


s 3

U n i t



e r s





4) PIPO (Parallel in-Parallel out)

The PIPO acts as a storage device but keeps and processes the byte inparallel form.

PIPO Shift Register

Special Devices

1. There are counters which will count in both directions. They are called"Up/Down" counters.

2. Some shift registers will move out in both directions. These are called "ShiftRight/ Shift Left" registers.

3. Very high speed systems use special flip-flops called "Master/SlaveFlip-Flops". The external connections are the same as an ordinary JK

flip-flop.

M o d u l e


s 3

U n i t



e r s












UNIT 7 THE COMPUTER



M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





TABLE OF CONTENTS

Para Page


4.1 INTRODUCTION 4

4.2 MEMORIES 4


4.3 READ ONLY MEMORIES (ROMS) 4

4.3.1 EPROM's and EEPROM's 7

4.4 RANDOM ACCESS MEMORIES (RAM) 8

4.4.1 Static RAMs (SRAM) 8

4.4.2 Dynamic RAMs (DRAM) 8

4.5 HARD DISKS AND FLOPPY DISKS 10

4.5.1 Hard disk 10

4.5.2 Floppy Disk 12

4.5.3 Magnetic Data Readers 13

4.6 CLOCKS 14

4.6.1 The Multivibrator 14

4.6.2 The Mains Supply and a Schmitt Switch 15

4.6.3 The 555 Timer 17

4.6.4 The Crystal Oscillator 19

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s







• Explain the terms ROM and CD ROM.

• Explain the terms PROM, EPROM and EEPROM.

• Explain the terms RAM, SRAM and DRAM.

• Explain the terms Hard disk and Floppy.

• Explain the use of a Streaming Tape,

• Explain the terms Hardware, Firmware and Software.

• Sketch a typical Multi-Vibrator and show how the timing can be changed.

• Sketch the circuit of a 555 timer, and show how the timing can be changed.

• Sketch a typical Crystal Clock and explain its frequency of operation.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.1 INTRODUCTION

The aim of this unit is to explain in basic terms the memories and clocks used in acomputer.

4.2 MEMORIES

4.2.1 Introduction

Digital memories are units which store information. The information is for use whenchecking control loops, storing operating programmes (PI and D settings), orremembering numbers during calculations etc. This unit will introduce the basic

concepts of how digital memories are made.

4.3 READ ONLY MEMORIES (ROMS)

A ROM is a permanent memory. It cannot be changed by the operator. It has datawritten into it which can be read from the memory but it cannot be removed. Thedata cannot be destroyed even if the supply is switched off.

Figure 4-1 Simple Diode Operated ROM

Figure 4-1 shows a simple diode operated ROM. The programmer positions thediodes to link the rows and columns into a matrix. In this program there are threeaddress lines and 4 output data lines. With the diodes in the positions shown theprogram operates as follows.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





If there is no diode linking the row to the column, the output is high (1). If there is adiode linking the row to the column when the row is earthed, the output is low (0).

The programmer can change this program by moving the diodes to new Positions.The resistors are added to limit the current through the diodes.

The data output for a ROM with diodes as shown in Figure 4-1 is given below:

This type of memory is usually called HARD WIRED. The program can only bechanged by manually changing the position of the diodes. For example, if diode A ismoved to position B (see Figure 4-1) then the data output for address 101 willchange from 1110 to 0111.

This type of memory is still used in ESD systems (e.g. Thorn-EMI fire and gasdetectors). This gives maximum safety as only an instrument engineer can movethe diodes to change the programme. The keyboard operator cannot change theROM program by mistake.

The diode matrix shown in the diagram is also manufactured as an integrated

circuit. However bipolar or field effect transistors are usually used to link the rowsand columns (not diodes). It works in the same way but the switch is more accurateand faster. This type of fixed memory is used when a manufacturer intends to massproduce a device, eg. a calculator. You use the keyboard to address the setprogramme of the memory. The answer is displayed on a screen.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





Another kind of ROM is the Programmable Read Only Memory (PROM). Thesecome with all the rows and columns linked by transistors so that all the outputs are

set at "0" as shown below.

The user can then program the device by selecting different line/column junctions.When you pass enough current through the junction it will blow the fuse link, andchange the output from 'TO" to “1”

There are several TTL PROM's available e.g. 74186 (64 x 8) and 74470 (256 x 8). There are also devices to program them.

Note:

64 x 8 means 64 output words of 8 bits. 64 = 26 so you need 6 address lines to get

the correct output words.

PROM's are popular with manufacturers of washing machines, ovens, etc. Theyallow flexibility in design.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.3.1 EPROM's and EEPROM's

Both these devices store a charge. The MOSFET insulation gate is used like acapacitor. It either holds a charge: " 1 " or it doesn't hold a charge; "0".

The EPROM (Erasable Programmable ROM) has a window in the top. By shiningultraviolet light through the window the program in the chip can be erased. Then thechip can be reprogrammed. The basic problem with this type of chip is that all theprogram must be destroyed before any changes can be made.

The EEPROM (Electrically Erasable Programmable ROM) is a device which isprogrammed using an electrical signal. A voltage of about 21 volts applied for about10ms will erase a single bit of the programme. This device is must easier to usethan the EPROM, as no ultraviolet light is required. You do not need to remove it to

reprogram it. Examples of the above chips are:

EPROM Intel 2716

EEPROM Intel 2817

EEPROM's provide the operating program in many of the PLC systems used in thefield. You will see these and program them when you practice basic configuring ofthe Allen Bradley PLC in the workshop.

Note

1 . The latest type of EEPROM is called a FLASH memory. This is an EEPROMwhich can be erased and programmed while it's in place. However, all thememory is removed when changes are required. The memory is removed ina "flash". An example is the INTEL N 28FO10-200 chip. This will remember131072 words (word length 8 bit) sometimes written as a 132 k bytememory.

2. PROMS, EPROM's and EEPROMS are programmed using special devicessupplied by the manufacturer. Normally the engineer programmes thesechips in the office. Then you change the whole chip in the field.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.4 RANDOM ACCESS MEMORIES (RAM)

As discussed in the previous section the ROM will store data permanently, (it isnon-volatile). However changing the programme is difficult, if not impossible.EPROM's and EEPROM's can be erased and rewritten but they cannot be changedat normal operating speeds. Therefore, another type of memory is required whichcan be re-programmed as required. These memories are called read/write orRandom Access Memories (RAMs).

4.4.1 Static RAMs (SRAM)

The simplest RAM is the flip-flop which will store 1 bit of data. FlipFlops connectedto make a resister can store a word. Connecting resisters together will produce a

very simple memory. The TTL 74170 4x4 register contains 16 flip-flop's. It can store4 words of 4 bits each. The TTL type RAM cannot be made very large because itloses a lot of power (heat). Normally MOSFET technology is used to make what arecalled "STATIC RAMs". These static RAMs contain thousands of flip-flop's on oneIC chip. This produces a large random access memory.

A typical static RAM is the Toshiba CMOS TC 55257 BPI-102. This will remember 132k byte and pass them out 8 bits at a time. This chip comes in a 28 pin DILpackage so you can connect it to a PCB.

4.4.2 Dynamic RAMs (DRAM)

Single Transistor Dynamic RAM Storage Cell

Dynamic RAMs are devices which can store a charge. A single cell is shown above. A charge in the capacitor indicates a "ONE". These devices can only store theinformation for about a milli-second, so that the data must be refreshed (rewrittenafter a short period of time). These devices are popular because each cell area issmall so a large memory can be created in a single device. An example is the

Motorola 65536 (64k) x 1 high speed dynamic RAM. This will store 64k bits but onlysend them out one at time.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





Note

1) Dynamic RAMs need a lot of external hardware. For example, they need a

counter, a clock for the counter and a mulitplexer to send row addresses,column addresses and a refresh count. They are still popular becausedynamic RAMs are much cheaper per bit of information stored,

2. Chip manufacturers are developing larger and faster static and dynamicRAMs all the time. Any electronic magazine will give you the latestdevelopments.

Static and dynamic RAMs are "volatile" memories. If you switch off the power, thedata is lost. Therefore, most systems have standby batteries or an UninteruptablePower Supply (UPS) system. This provides power if mains power is lost.

The Motorola 64 K DRAM comes in a 16 PIN DIL package with pin connections asshown.

This type of memory is used in most personal computers. It is also the type ofmemory used when changing the operating conditions for a loop.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.5 HARD DISKS AND FLOPPY DISKS

Static RAMs and Dynamic RAMs are used inside computers. They remember

changes that the typist makes on the P.C. or the operator makes on a control loop.However, these devices soon become full. Therefore, other types of RAM are usedto store large' quantities of information which must be kept for a long time. Theseare called hard disks and floppy disks (floppies).

4.5.1 Hard disk

Figure 4-2 A Typical Hard Disk Drive Unit

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





Figure 4-2 shows the layout of a hard disk drive unit. It consists of a number ofmagnetic disks. These store the information in much the same way as a musiccassette tape.

Information can be written on or read off the disk electronically. The electronicsdrive motors. The motors set the position of the disk and the position of the readinghead so it will process the required data. The hard disk drive used in the office P.C.will store about 0.5 G bytes of information. The hard disk will hold all the necessaryinformation. This information can be changed and rewritten as required.

The hard disk unit on a DCS in a plant is called the HISTORIAN. The historian canbe very large (many Giga bytes). It will hold and update information about the plantover many weeks.

The hard disk will also hold the software programmes. These are programs which

are designed to do particular jobs such as typing, making diagrams, doingcalculations, etc. Windows 95 is a good example of a modern software system.

A DCS system has software specially made to show the PFD's for the plant on theVDU. These software programmes are supplied by the manufacturer to fit your plantand are stored on the system hard disk.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.5.2 Floppy Disk

Figure 4-3 Floppy Disks (Diskettes)

Figure 4-3 shows 2 typical floppy disks. These disks come in various sizes (e.g. 8in., 51/4 in., 3.5 in., etc.). They are used to store information that is no longerneeded on the hard disk. When this course was written it was kept on a hard diskuntil it was finished. Then it was put onto a floppy and kept until it was needed. Thefloppy also acts as a back-up for the hard disk in case of hard disk failure.

A DCS system keeps the plant programmes on floppy disks as a back-up for thehard disk drive. Also, the engineer may have his own floppies which he hasprogrammed himself. These may be used to run a maintenance schedule to checkthe system micro-processors etc.

A floppy disk drive works in much the same way as a hard disk drive. The differenceis that you must insert the disk (the floppy) into the disk drive yourself.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.5.3 Magnetic Data Readers

The diagram shows the basic principle of a magnetic data reader. The tape/disk hasa thin coating of magnetic iron oxide. When a current is passed through the coil aflux is produced across the gap in the iron core. This magnetises the tape/disk sothat a ONE or ZERO is recorded at that particular position. The digit depends on thedirection of the current (i.e. the polarity of the induced magnet). The system isreversible. The magnetised tape/disk is passed over the head. As magnetised areason the tape pass under the tape head gap, a magnetic field is formed in the soft iron

core. The variations in the field induce voltages across the coil. These voltages areamplified to produce ONE's and ZERO's according to the data stored on the tape.

Note:

1. The latest type of programme storage method is the Compact Disc ReadOnly Memory (CD ROM). This is the same type of disk as is used in a CD ina home music system. These are read using a light source (laser). They arebetter than the old magnetic disks because the data cannot be damaged bystray magnetic fields.

2. In some systems the RAM is a cassette type tape unit. These are common

in large computer facilities as they can store Tera bytes of data. Foxborouses them as back-up units for the main hard drives. Foxboro calls them"Streaming Tape" drives.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.6 CLOCKS

4.6.1 The Multivibrator

The basic clock or timer for digital work is the free running flip-flop (multi-vibrator).This is easily made using two BJTs as shown in Figure 4-4.

Figure 4-4 The Multi-Vibrator

OPERATION:

When the circuit is turned on let's assume that T1 conducts more than T2. Thecollector of T1 will fall and the resulting negative charge is transferred through C1.This will tend to cut off T2 and produce a rise in T2 collector. This rise will drive T1

further on so that T1 will go "FULL ON" and T2 "OFF" almost immediately. This statewill not last. The charge of C1 will immediately drain through R2 and R A until thevoltage on T2 base reaches the "CUT ON" point. At this point T2 Will "CUT ON".When T2 Cuts on its collector voltage will fall. This fall will "CUT OFF" T 1. This stateis also unstable as C2 drains through R, and RB, so that T1 will again "CUT ON" asT2 "CUTS OFF". This operation continues as long as the supply is switched on. The

outputs from the two load resistors are opposing square waves as shown below.

The frequency of operation is approximately 1/2 C (R + R A) Hz (if C1 = C2, R A = RB

& R1= R2). If the transistors are the same the output will have an even mark tospace ratio

This circuit is, not very stable and operates only at low frequencies. However, it is a

very simple and cheap clock.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.6.2 The Mains Supply and a Schmitt Switch

In some countries the frequency of the mains supply is very stable all day. So, it can

be used as a timer for electronic clocks, etc.

The diagram below shows a circuit used to obtain 50 Hz T.T.L level pulses from themains supply.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





The Schmitt switch is a very useful device. You can buy it as T.T.L (7414) or CMOS(4554). It has two trigger levels. One level is for positive going signals and one is fornegative going signals. The Schmitt switch is usually shown with a "NOT" output.

This means the output is high when the input is low.

Another important use for the Schmitt switch is for telephone and radio signals etc.The digital signals are distorted as they pass from the transmitter to the receiver.The Schmitt switch can be used to restore the distorted signal. The diagram belowshows this using a 7414.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.6.3 The 555 Timer

The 555 timer is an IC which is good for low frequency non-precision timing work. It

comes in either T.T.L (LM 555) or CMOS (LM7555).

The basic circuit is given in Figure 4-5.

Figure 4-5 Basic Circuit of 555 Timer

The chip consists of an RS flip-flop with reset, upper and lower comparators and aconstant current discharge transistor.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





OPERATION:

1 . The three 5 kΩ resistors inside the chip set the control voltages for the

upper and lower comparators. When the unit is switched on (+Vcc applied),the RS flip-flop is reset so that Q is low.

. External capacitor C charges through R A and RB. When the voltage across C(trigger) reaches the control voltage of the lower comparator, the comparatoroutput changes over. The change applied to the terminal of the RS flip-flopswitches the output Q to High. This change switches on the dischargetransistor.

3. The capacitor C will now discharge through this transistor. At a certain lowvoltage the threshold of the upper comparator is reached. At this point theoutput to the R terminal of the R/S flipflop output changes back to its starting

position. Then C starts to charge again.

4. The operation is continuous as long as the VCC is connected.

The output is a series of timed pulses depending on the charge time of thecapacitor.

The frequency of the pulse depends on the added components R A, RB and C where

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s





4.6.4 The Crystal Oscillator

Most computers must have a more accurate timing system than the timers

described in this unit. This is achieved using a "quartz crystal" such as the onesused in top quality watches.

A "quartz crystal" is a specially cut crystal that has a "pieso-electric" effect. At aparticular frequency it will vibrate to produce an electrical signal and vice-versa. Ineffect it is a very accurate tuned circuit. It's frequency of resonance depends mainlyon the size of the crystal and the way it is cut.

A typical 1 MHz TTL crystal oscillator is given in Figure 4-6. The crystal providespositive feedback at its resonant frequency. This means the circuit will oscillate atone frequency only. The crystal sets the frequency.

Figure 4-6 1 MHz Crystal

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

4 -

M e m o r i e s a n

d c

l o c

k s












UNIT 7 THE COMPUTER



M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s





TABLE OF CONTENTS

Para Page


5.1 INTRODUCTION 4

5.2 MULTIPLEXERS 4

5.3 DECODERS (DE-MULTIPLEXERS) 5

5.4 THE BCD DECODER 5

5.5 THE SEVEN SEGMENT DISPLAY 6

5.6 THE LIQUID CRYSTAL DISPLAY. 8

5.7 MATHEMATICAL NOTE 9

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s







• Explain the purpose of a multiplexer

• Explain the purpose of a decoder

• Describe the LED and LCD 7 segment display

• Explain the use of the 7 segment code.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s





5.1 INTRODUCTION

The aim of this unit is to explain the purpose of multiplexers, decoders and displays.

5.2 MULTIPLEXERS

Multiplexers are devices which combine different analog or digital data signals intogroups. This data can then be transmitted over a single cable. Multiplexers are verycomplicated devices. They are normally serviced and operated by thetelecommunication department. However, simple single chip multiplexers are foundin some instruments. A typical example is the MAX. 378 which will multiplex 8analog signals for onward transmission.

One type of multiplexer is a device called a "UART".

The UART (Universal Asynchronous Receiver Transmitter) takes signals from the

µP system in parallel form and changes them to a serial form for transmission. It will

also, receive serial input signals and convert them to parallel 'for µP processing.

Figure 5-1 shows in simple terms the use of a UART.

Figure 5-1 UART

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s





5.3 DECODERS (DE-MULTIPLEXERS)

Decoders (de-multiplexers) take in a stream of data. They convert the data so that itcan be displayed or processed by a µP. There are various types of decoder(de-multiplexer) depending on their use.

74138 : This decoder/de-multiplexer takes in 3 input data lines and produces8 output lines.

74154: This decoder/de-multiplexer takes in 4 input data lines to provide 16output lines. This chip is used in your workshop project.

5.4 THE BCD DECODER

An important decoder is the BCD decoder. This converts BCD into a special code todrive a digital display (seven segment display).

A block diagram of how a digital display is done is shown below.

The decade counter counts the input signal pulses and provides a 4 line address inBCD to the "BCD to 7 segment.7 decoder. The output from the decoder is amplifiedby the driver to operate the display.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s





5.5 THE SEVEN SEGMENT DISPLAY

This is the standard method for digital displays on all electronic indicators. The twocommon types of seven segment display use either LEDs or an LCD as follows:

Figure 5-2 The LED 7 Segment Display

Figure 5-2 shows a typical 7 segment LED display. Seven LED's are shaped and

placed in an insulating substrate (usually a ceramic). The position and-connection ofeach lettered LED is standard. Therefore, all LEDs will have "a" at the top and "d" atthe bottom and so on. The device shown has the anodes of the LEDs connectedtogether (common anode). The LED is lit by the BCD decoder-driver which earthdifferent cathodes as required.

The LED display can also be obtained with all the cathodes connected together(common cathode). In this case a positive voltage Is provided by the BCDdecoder-driver which lights the correct LED.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s





Figure 5-3 Digital Display of Numbers using Seven Segment Code

Figure 5-3 shows the illumination required to make a seven segment digital display.For example, to display the number 3 - a,b,c,d and g must light, but f and e must notlight.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s





5.6 THE LIQUID CRYSTAL DISPLAY.

This is the display usually used by a calculator. The seven segment code is used forthe display in the same way as an LED. However, the method of illumination isdifferent, as follows:

Figure 5-4 The Basic LCD Display

Figure 5-4 shows a simplified diagram of an LCID display. The liquid crystal issealed between two plates of glass. The segments are set into the liquid. When avoltage is applied to the segment it produces an electrical field across the liquid.This makes it absorb light and so the segment looks black. When the voltage isremoved it will reflect light and so it looks white again. In the diagram a b and chave a voltage applied (black),f, e, g and d have no voltage applied (white). Thenumber 7 is displayed as a black figure on a white background.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s





5.7 MATHEMATICAL NOTE

ADDING BCD

There is a problem when adding BCD as a 4 bit binary code. It will producenumbers from 0000(0) to 1111 (15). However, decimal will only allow 0000(0) to1001 (9) in any one column. After this the number must revert to 0000 and carry.Therefore, adding two BCD numbers is complicated. The calculator actually usesthe following method.

Note: Subtraction is done using ONE's complement and adding.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

5 -

M u

l t i p l e

x e r s ,

D e c o

d e r s a n

d D i s p l a y s












UNIT 7 THE COMPUTER



M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -

D i g i t a l / A n a

l o g

& A n a

l o g

/ D i g i t a l C o n v e r

t e r s





TABLE OF CONTENTS

Para Page


6.1 INTRODUCTION 4

6.2 D/A AND A/D CONVERTERS 4

6.3 BINARY WEIGHTED RESISTOR DAC 4

6.3.1 R/2R Ladder DAC 5

6.4 ANALOG TO DIGITAL CONVERTER (ADC) 6

6.4.1 Ramp Type ADC 6

6.4.2 Successive-Approximation ADC 7

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -


l o g

& A n a

l o g


t e r s







• Explain the use of a DAC

• Explain with a simple diagram the binary weighted resistor DAC.

• State the advantages of an R/2R DAC.

• Explain using a block diagram a modern DAC chip.

• Explain the use of an ADC.

• State the advantages of a successive approximation ADC over a ramp type

ADC.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -


l o g

& A n a

l o g


t e r s





6.1 INTRODUCTION

The aim of this unit is to explain the Digital to Analog Converter (DAC) and Analog

to Digital Converter (ADC).

6.2 D/A AND A/D CONVERTERS

Digital to Analog Converters (DAC) and Analog to Digital Converters (AD C) are anessential part of digital control. The DAC turns digital control signals into analogsignals for 4-20mA output loops, etc. The ADC turns analog signals from the inputloops (mA, mV, resistance, etc.) into digital signals for computer processing.

The following notes describe the techniques used. remember these converters areobtained as an I.C (not as discrete components

6.3 BINARY WEIGHTED RESISTOR DAC

The basic principle of a Binary Weighted Resistor DAC is simple. It uses a summingoperational amplifier. This is the circuit which was made during practical tasks inIndustrial Electronics Ill. Figure 6-1 shows the basic circuit for 'a 4 bit binary toanalog converter using binarv weighted resistors.

Figure 6-1 Basic Circuit for a 4 Bit DAC

The switches represent the input binary code and it works as follows.

1. With all switches open the output is 0 Volts.

2. If D0 is closed the output is -10 / 100 x 5V = - 0. 5V.

3. If D0 is opened and D1 is closed the output is -10/50 x 5V = -1 V.

4. If all four switches are closed the output is -5 x (10/12.5 +10/25+10/50+10/100) =-5x(0.8+0.4+0.2+0.1) = -5 x (1 .5) = -7. 5 V.

5. So if the switches are operated by a binary code the output will be from 0 volts to -7.5 in 15 steps of -05V.

The range of the output can be adjusted by RF but the maximum will be about -14V dueto the saturation of the OP-AMO.

The above system is not much good if the input is larger than 4 bits as the range ofthe resistors becomes to large.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -


l o g

& A n a

l o g


t e r s





6.3.1 R/2R Ladder DAC

Figure 6-2 Basic R/2R Ladder DAC

A basic R/2R ladder DAC is shown in Figure 6-2. This is the normal method used bythe I.C. manufacturer. The circuit is shown at the zero position with all inputs atzero. The binary input changes the switches (D0 to D3) to provide an output with thesame voltage steps as the previous DAC. However, the analysis of the circuit iscomplicated and not worth remembering. The R/2R DAC has the advantage of onlyrequiring 2 values of resistor. Therefore, it is much easier to manufacture on an IC.chip.

Modern D/A converter chips have input latches, decode logic (electronic switch), anR/2R DAC and an output amplifier all on one chip. They will accept either serial orparallel digital data inputs. A typical example of an instrumentation DAC is the MAX.502. This accepts a 12 bit parallel input and produces an output voltage suitable fordriving a 4-20mA output loop.

Note: The latches collect the 12 bit input data. They pass the input data to the

decoder logic and DAC when ordered by the µP using the write line.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -


l o g

& A n a

l o g


t e r s





6.4 ANALOG TO DIGITAL CONVERTER (ADC)

6.4.1 Ramp Type ADC

Figure 6-3 Ramp Type ADC

Figure 6-3 shows a ramp type ADC. The principle of operation of this type of ADC issimple. The ANALOG and RAMP signals are applied to a single comparatorOP-AMP. The comparator will have an output if the analog signal is greater than theramp voltage. The comparator output and a clock signal are both fed to an ANDgate together. The pulsing output from the AND gate is fed to a binary counter. Thecounter will count until the RAMP voltage reaches the level of the analog signal.Then it will stop. The system then resets and counts again. The binary counter willchange every count cycle so that it follows the changes in the analog signal. Thetiming and control unit opens the latches at the end of each count. This provides a16 bit parallel data output.

As an example, suppose the RAMP is set to rise at 1V every 1 ms. If the analog

signal is 2 volts then the counter will count for 2ms before stopping and resetting.The number of counts will be

2/1000 x 1000000/1 = 2000

if the analog signal then falls to 0.5 volts then the count reduces to 500.

The problem with this type of ADC is that there are variations in the ramp generatorslope. This is caused by temperature and voltage variations. Also it is slow. A countof 20 000 will take 100ms or more per conversion cycle.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -


l o g

& A n a

l o g


t e r s





6.4.2 Successive-Approximation ADC

Figure 6-4 Basic layout of Successive Approximation ADC Chip

Figure 6-4 shows the basic layout of a successive approximation ADC. Remember

all of this is made on one chip (e.g. MAX 166 8bit ADC).

The great advantage of this type of converter is its speed. It will produce ONE bit ofresolution for only ONE clock pulse. The problem is that it is more complicated andit needs a DAC to make it work. Therefore, it is expensive.

A brief explanation of the successive approximation method is given below:

1. The circuit consists of four units. A successive-approximation register (SAR),a DAC and two operational amplifiers.

2. At the start the output is zero. On the first clock pulse the full output fromOP-AMP A will be applied to the SAR. This produces a ONE at the MS13position. This ONE is then D/A converted and returned to OP-AMP A viaOP-AMP B. The SAR waits for the result of this comparison.

3. If the DAC signal is greater than the input then the SAR MSB reverts to zeroand the next clock pulse operates the next MSB.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -


l o g

& A n a

l o g


t e r s





4. If the D/A signal is less than the input then the SAR keeps a ONE in MSBposition.

5. The SAR will then continue trying the next MSB until it is full.

6. The output will be a series of ones and zeros according to the analog inputsuccessively approximated to the number of digits the SAR willaccommodate.

7. At the end of the count the latches open to provide a parallel output. TheSAR also provides a serial output if required.

8. If the output "End of Conversion" is connected to the "Start of Conversion"(SC) then the converter will continuously recycle.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U

n i t N o .

6 -


l o g

& A n a

l o g


t e r s












UNIT 7 THE COMPUTER



M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

7 -

T h e

C o m p u

t e r





TABLE OF CONTENTS

Para Page


7.1 INTRODUCTION 4

7.2 THE COMPUTER BLOCK DIAGRAM 4

7.3 THE MICROPROCESSOR 6

7.4 CONCLUSION 7

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

7 -

T h e

C o m p u

t e r







• List the main parts of a computer and explain their use.

• Explain the terms hardware, firmware and software.

• Explain the term bus.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

7 -

T h e

C o m p u

t e r





7.1 INTRODUCTION

The previous chapters have discussed the basic digital building blocks. Thepurpose of this chapter is to show how these blocks go together.

7.2 THE COMPUTER BLOCK DIAGRAM

Figure 7-1 Computer Block Diagram

Figure 7-1 shows the components of a simple single-board computer.

The functions of each components are as follows:

a) Keyboard:

This may be the same as a typewriter keyboard (e.g. secretary's PC). It maybe specially designed for a particular purpose (e.g. refinery control). You willlearn how to use a particular keyboard during specialist equipment training(e.g. Foxboro IA, Honeywell TDC 3000 etc.).

b) Keyboard Input Unit:

This changes the signals from the keyboard into an ASCII code so that thesignals can be understood by the microprocessor. These signals arechanged from serial to parallel form using standard shift registers. Thekeyboard will also provide signals so that the computer can be programmed.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

7 -

T h e

C o m p u

t e r





c) Memory Unit:

This is the working memory for the computer. RAM's depends on the size of

the computer. The number of RAM’s depends on the size of the computer.

d) Timing Unit (Clock):

This consists of a crystal oscillator and ROM. The ROM programmes thetiming pulses from the clock. Different microprocessors operate timers indifferent ways.

e) 1/O Units (input/output Data Chips) :

These connect the computer to the outside world. They may includeparallel/serial converters, DACs and ADCs etc. The type of chip which is

used depends on the data being sent or received.

f) Power Supply Unit:

This is a standard 230V/5V DC power supply. It's similar in design to theones made during Industrial Electronics 2.

g) VDU Output:

This unit produces the characters which will be displayed on the VDU screen. TheRAM stores the data to be displayed. When the data is called up a charactergenerator displays the information on the screen.

h) Interface Unit to Disk Drives:

This unit collects/sends data to/from the disk drives fitted into the computer.There are usually two drives. One drive takes a floppy disk at the front of themachine. The other drive is the hard disk drive inside the machine.

Note: The connections between the chips are extremely complicated. It is onlypossible to do these using a multilayered printed circuit board. They aredesigned by the manufacturer and made as a particular item for the PCin use. You can not make your own computer without a special machine

for making PC boards

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

7 -

T h e

C o m p u

t e r





7.3 THE MICROPROCESSOR

This is the most important unit in the computer. It processes the incoming data,

carries out calculations as required, and returns the results to the outside world.Figure 7-2 shows a block diagram of the ZILOG Z 80 CPU (Central ProcessingUnit) microprocessor. The diagram shows the pin configuration i.e. the way the pinsare arranged. This operates on an 8 bit data bus (8 wires) and a 16 bit address bus(16 wires). 8 BIT DATA

8 BIT DATA

Figure 7-2 ZILOG Z 80 CPU

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

7 -

T h e

C o m p u

t e r





7.4 CONCLUSION

The previous units have introduced the chips required to make a digital computer

control system. The actual instrument control system used in the field varies fromcompany to company. This must be learnt on the job.

The instrument course on the "Introduction to Process Control" gave a shortintroduction to the Foxboro IA and Honeywell TDC 3000 as examples of DCScontrol. However, you may work on the Bailey INFI 90 DCS or the Rosemount RS3DCS.

This course, "Industrial Electronics 4", has introduced what is called theHARDWARE (the chips and components that make up digital control).

The operating instructions for the microprocessors and the computer are set by the

manufacturer in the operating ROM's. These instructions are called FIRMWARE.

The systems engineer programmes the DCS to fit the plant he is working on usingwhat is called SOFTWARE. This software is provided by the manufacturer (e.g.Foxboro) to operate his system only. Usually this comes in the form of a floppy discor streaming tape. This data is loaded into the hard disk on start-up.

The Z80 is used as an example of a microprocessor chip. There are many moretypes of chips in use. The newest chips have a 64 bit data address. However, theyall work in the same way.

The blocks provide the following functions:

1. The 16 bit address bus is used by the CPU to address the RAM's, ROM'setc. to gather or send data required for processing.

2. Data comes in and out through an 8-bit bus.

3. The ALU (Arithmetic Logic Unit) performs the required data calculations.

4. The Inst. Reg. (instruction register) holds the instructions as required. Thisallows the "Instruction Decode and CPU control" unit to perform the requiredsystem and CPU control.

5 The CPU registers do many jobs;

• They act as short time stores (accumulators) for the ALU.

• They acts as memory refresh for dynamic RAM's.

• They act as a program counter

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

7 -

T h e

C o m p u

t e r












UNIT 7 THE COMPUTER



M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





TABLE OF CONTENTS

Para Page


8.1 INTRODUCTION 4

8.2 SERIAL TRANSMISSION 4

8.3 PARITY 5

8.4 A TYPICAL TRANSMISSION SYSTEM 6

8.5 THE MODEM 7

8.6 RS 232C 9

8.6.1 The RS 232C Connector 10

8.7 HANDSHAKING 11

8.8 GLOSSARY 12

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n







• Sketch a typical serial digital transmission signal.

• Explain parity

• Explain the use of a modem

• State the main types of modulation

• Explain the terms DTE and DCE.

• Explain why RS 232C is used.

• Explain handshaking

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





8.1 INTRODUCTION

In the oil industry a Distributed Control System must be able to send operationaldata from the outlying platforms to the main control room. This final chapter tellsyou something about how this data is sent using digital transmission.

8.2 SERIAL TRANSMISSION

Serial transmission reduces the number of communication links (e.g. telephone wirepairs or micro-wave links etc.) which a system needs. Serial transmission allowsthe-required data to be sent as a series of bits on a single pair of wires or achannel.

Figure 8-1 A Serial Digital Transmission Signal

Figure 8-1 shows a typical byte (character) sent in a serial form. It consists of 11bits of data. The start and stop bits are always the same so that the receiver of theserial signal knows which part of the byte to decode. Parity is explained in the nextsection. The actual message is a seven bit word. A group of these bytes makes upthe full data. The data is sent one word at a time. The real meaning of the messagedepends on the programme used. It will have to be decoded correctly at thereceiving end before it can be displayed.

The speed of the transmission is called the "Baud Rate". This is 1 divided by thetime for one bit. For example if the bit time is 1.66 ms then the baud rate is

A high "Baud Rate" means faster transmission.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





8.3 PARITY

As can been seen from the previous work if a "ONE" bit changes to a "ZERO"during the transmission of digital information the whole meaning of the messagechanges. To reduce errors a PARITY system is used. Figure 8-2 shows a typicalparity transmission system. The "parity generator and checker" on the sender findsout if the message has an ODD or EVEN number of ONEs (e.g. 01101101 has anodd number of ones). If the number is ODD a high signal is sent to the receivingend, if EVEN a low signal. The "parity generator and checker" on the receiver alsoworks out if the number is ODD or EVEN. If it agrees with the sender then the datais passed. If it does not agree it sends a return signal so that the sender transmitsthe data again.

Figure 8-2 Parity Checking of Parallel Digital Transmission

The example given shows parity checking for a parallel data transmission system.Normally this is only used over short distances, such as within the computer itself.Parity checking is also used on serial transmission. The parity bit is placed at the

end of the message (see Figure 8-1). This is a 1 if the message bits are odd and 0if the message bits are even. The receiving equipment adds up the number of onesin each message. It checks this number against the parity bit to see if a bit has beenlost in transmission. If the parity check shows a fault the receiver sends a serialmessage back to tell the transmitter to send again.

The "parity" method does not work if two errors occur. If two bits are lost themessage will still appear odd or even and the system will think the information iscorrect. There are error correction systems which use more than one "parity" link.These systems use what are called "Hamming codes".

These codes are not covered in this unit. However, students working on data

transmission "unit to unit" will cover these codes later on.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





8.4 A TYPICAL TRANSMISSION SYSTEM

Figure 8-3 Basic Data Transmission System

Figure 8-3 shows the basic steps used to send data by radio link.

The information from the transmitters is digitised and processed through themicrocomputer. The processed information is put into serial form by a PISO registerand fed into a modulator (modem). The modulator drives the radio transmitter (Tx).

The receiver (Rx) picks up the radio signal. The signal is then changed back toserial digital form by the receiving demodulator. Next, it is put into parallel form by aSIPO register. Finally, it is processed by the microcomputer for display on thereceiving station's VDUs.

Note: The block diagram shows a signal being sent from a remote station tothe main control center. Most systems are capable of working in bothdirections; each end can work as a receiver or transmitter. Themodulator and demodulator are combined into what is called a MODEM.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





8.5 THE MODEM

A MODEM is a unit which changes the serial data of the input so that it can

modulate the transmission system (e.g. telephone wire pairs, radio link, satellitechannel, etc.). Modulation is the process which puts the data onto a carrier wave sothat it can be sent long distances through the atmosphere. It can also do theopposite. It converts the incoming signal to a serial data form (demodulates). Thereare many systems for doing this. These systems will not be dealt with in this unit.They are the work of telecoms technicians. However, some trainees may coverthese systems at a later date.

The four main methods of modulation are:

1 ) Amplitude Modulation (AM)

There is a carrier frequency for a "ONE" but not for a "ZERO"

2) Phase Shift Modulation (PSM)

The sine wave carrier reverses phase (inverts) from a "ONE" to a "ZERO".

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





3) Frequency Shift Keying (FSK)

The frequency jumps from one frequency to another depending on the data.

Note:

a) A similar system is used by the new digital telephones. A different frequencyis used for each number.

b) This method is popular as modems can pass information in both directionsat once (duplex mode) using four different frequencies. Two frequencies areused to send data and two frequencies are used to receive data.

4) Time Division Multiplex (TDM)

In this system, various groups of data are sent on the same transmission frequency.However, they are separated in time. This system is also used to multiplex datawithin the microprocessor. The diagram show three messages being sent at onetime.

The messages A B and C are split into small parts and sent together in one secondintervals. The receiver then separates the small parts and puts all the As, all the Bs,and all the Cs together to make the real message. This method is used for satellitetelephone calls. About 20 calls can be made at the same time on one channel. Thetime for each part of the call is in milliseconds. It is so fast that the listener cannotdetect that he is listening to a message in bits.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





8.6 RS 232C

Modems and the transmitting and receiving equipment that go with them are often

called Data Communication Equipment (DCE). The terminals and computers whichsend or receive the serial data are called Data Terminal Equipment (DTE). In orderto have standard connections between DCE's and DTE's the USA "ElectronicsIndustries Association" (EIA) published the following standard; RS232C. Thisstandard is used all over the world.

This standard defines the voltage levels of the signal, the handshake signals, and astandard 25 pin connector.

DTE - DATA TERMINAL EQUIPMENTDCE - DATA COMMUNICATIONS EQUIPMENT

Figure 8-4 Block Diagram of a Communication System

Figure 8-4 shows the basic block diagram of a communication system usingmodems.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





8.6.1 The IRS 232C Connector

Figure 8-5 RS 232C Pin Connections

Figure 8-5 shows the RS 232C signal names and pin numbers

A basic explanation of the operation of the system is as follows:

1 The "Power on" terminal runs self - checking routines.

2. The Terminal sends a DTR signal to the MODEM

3. The MODEM replies DSR to indicate it is ready.

4. The MODEM at the receiver end is dialled.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





5. The receiver MODEM sends a ready signal. This is on a frequency of 2225HZ on telephone lines.

6. When the transmitter MODEM gets this ready signal it sends a- CD signal tothe terminal.

7. The terminal sends an RTS signal back to its MODEM.

8. After a set time the transmitter MODEM sends a CTS signal to the terminal.

9. The terminal sends the data in serial form through the TXD output.

10 .The same steps are followed at the receiving end.

8.7 HANDSHAKING

Handshaking is used to ensure that the two ends of a communication link are readyto receive transmitted information. This is particularly important when a duplexsystem is used. For example, using telephone wires, the transmitting modem willnot send until it receives a high signal (2225 Hz) from the receiving modem (answermode modem).

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





8.9 GLOSSARY

The following is a list of definitions of the terms used in industrial electronics and

can be used as a review of the course:

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n





M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

8 -

I n t r o

d u c

t i o n

t o d a

t a t r a n s m

i s s i o n












UNIT 7 THE COMPUTER



M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





TABLE OF CONTENTS

Para Page

INSTRUCTOR'S NOTE 3

PRACTICAL TASK 1 4

PRACTICAL TASK 2 7

PRACTICAL TASK 3 10

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





INSTRUCTOR'S NOTE

An instrument technician is not expected to service electronic cards. The digitalelectronic course is concerned with what a chip does, not how it works. Therefore itis suggested that the practical tasks for this course be done in the form of projects.

Three simple projects are enclosed which have proven successful in the past.However, other similar projects can be carried out to fit the chips readily available inthe Company. A book which may help is "301 Circuits" by Micro-Tech Publishers.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 1

THE MULTIVIBRATOR AND BINARY COUNTER

Components required.

QUANTITY DESCRIPTION

2 BC 109

2 10k Resistors

2 2.2k Resistors

2 10µF Capacitors

1 4024

7 250Ω Resistors

7 Red LED’s

1 PC Board

Procedure:

1 ) .Construct the given circuit on a PCB board. Remember to make sure thatthe copper strips are broken in the correct places.

2) Connect up the 9V supply (power supply switched OFF).

3) Switch ON the power supply. If the circuit is counting correctly the LED's willlight in a binary sequence until they are all lit (the binary number 1111111).

4) If the circuit does not work. Start fault finding by checking that themulti-vibrator produces pulses first.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





Questions to show understanding of project.

Q1) What is the maximum decimal count of the binary counter?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

Q2) How could you re-set the counter manually?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





CIRCUIT DIAGRAM BINARY COUNTER

4024 PIN CONNECTIONS

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 2

BACK AND FORTH FLASHER

The object of this project is to produce a back and forth flasher. This is often usedas a brake warning light on a car. It will demonstrate the use of a 555 timer, up anddown counter, 7400 NAND logic gate and a 44ME to 16 4ME decoder(demultiplexer).


Procedure:

1) Construct the circuit as given in the diagram. Remember to break the copperstrips as required.

2) When you have made the circuit check it for mistakes.

3) Connect the circuit Vcc to the positive terminal of a 5V dc supply. Earth thenegative terminal together with the circuit earth (make sure the power supplyis switched OFF).

4) If you have been successful in your construction, the LEDs will flash backand forth when you switch the supply ON.

If it does not work switch OFF. Check the circuit again. With patience you will findthe fault and get it to work.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





Questions to show understanding of project.

1) How could you change the fishing rate ?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

2) Why is the UP/DOWN counter added?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





Note: Pin connections on diagram. Vcc = + 5V

Circuit Diagram Back and Forth Flasher

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 3

A 0-99 COUNTER

The aim of this project is to use a decade counter, BCD decoder/driver and a 7segment display to make a 0-99 counter. This counter is made using a commoncathode LED display. If a common anode display is used the BCD decoder/driverwill be 7447.


Procedure:

1) Construct the circuit as shown in the given diagram.

2) Set the function generator to give a 1 Hz square wave output. Apply the TTLoutput to pin 14 of the first counter (IN position). See if you can get it towork.

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s





Note: Pin connections on diagram. Vcc = + 5V

Circuit Diagram 0-99 Counter

M o

d u

l e

N o .

6 :

I n d u s

t r i a l e

l e c

t r o n i c

s 3

U n

i t N o .

9 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 7

INSTRUMENT WORKSHOP



July 1999- Rev.0

Page 1/18




M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 2/18


TABLE OF CONTENTS

Para Page

PRACTICAL TASK 1- 4

1.1 OBJECTIVES 4

1.2 PRACTICAL NOTES 5

1.2.1 Types of Packing 5

1.3 PACKING REPLACEMENT 8

1.3.1 Removing Old Packing 8

1.3.2 Installing New Packing 8

PRACTICAL TASK 2 12

2.1 OBJECTIVES 12

PRACTICAL TASK 3 18

3.1 SOLDERING 18

3.2 INTRODUCTION 18

3.3 GOOD P.C. BOARD SOLDERING 18

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 3/18


WORKSHOP SAFETY

The following safety procedures must be followed when doing practical work onvalves in the workshop or out in the field.

• The shop should be kept clean and free from hazards which might causeyou to slip or fall.

• Inspect your tools regularly; if your tools are worn and unsafe you shouldthrow them away.

• Neutralise any valve body which has been in contact with flammable,corrosive or toxic fluids.

• The employees should wear suitable clothing. If the clothing is contaminatedwith any harmful or flammable substances it must be cleaned before it isused again.

• Wear approved eye protection when you use compressed air to removerubbish from the equipment.

• To avoid a fire hazard or explosion, do not apply grease to valves which areused in oxygen systems unless the grease can be removed before the valveis put back in service.

•

The disc in a butterfly valve will fall out of the valve body if the shaft isremoved. To avoid injury to personnel and damage to the disc, you mustsupport the disc to prevent it from failing when you remove the shaft.

• Before you begin maintenance work or removal of any equipment in thefield, you must tell the process supervisor and get a work permit.

• If you are working above ground level you will need a platform of some kind.The platform-must be strong enough to support you, and your equipmentand tools. Platforms should have a raised edge to prevent objects fromfalling off.

• To avoid personal injury and damage to the process equipment, isolate thecontrol valve from the system and release all the pressure from the bodyand actuator before you take it to pieces. You must also relieve allcompressive actuator load on the shaft connection before performing anymaintenance operations.

• Do not clear out gas lines with air. Use steam, nitrogen or other approvedchemicals.

• Be very careful of compressed air or gases. Unfortunately, many employeeshave died while working on compressed air lines that they thought weredepressurised.

• Finally, read the manufacturer's instruction manual before starting work onany piece of equipment.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 4/18


PRACTICAL TASK 1.

REPACKING A STUFFING BOX AND DOING A LEAK TEST

1.1 OBJECTIVES

The student will :

1. Repack a gland following the procedure in the attached instructions.

2. Carry out a pressure test on the valve using the attached instructions.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 5/18


1.2 PRACTICAL NOTES

VALVE STEM PACKING

The purpose of valve packing is to prevent leakage. In a typical valve, the glandfollower is tightened until there is no leakage. The valve is then test-operated tomake sure that the packing is not compressed so tightly that the valve does not turneasily.

Note: Constant friction is not a problem in valve packing applications. This isbecause the opening or closing of a valve is a low speed operation.

Figure PT-1 Valve Stem Packing

1.2.1 Types of Packing

Packing comes in two types; in pre-shaped rings or in rope form which is cut to size.The common pre-shaped ring packing material is Teflon. This a plastic materialwhich is self lubricating. Normally the Teflon rings are held in place with a springbelow the gland follower. Another form of this type of packing is called "Chevron"packing. Teflon or rubber packing rings are shaped like a "V" (Chevron) and placedin the stuffing box as shown in Figure PT-2. The process pressure forces the edgesof the chevrons outwards against the shaft and stuffing box wall to produce a goodseal. Chevron packing is very common in hydraulic and pneumatic systems.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 6/18


Figure PT-2 Types of Packing

Rope type packing

Rope type packing comes in various styles and a few examples are shown in FigurePT-2. The most common materials used to make these ropes are Teflon/Asbestosor graphited asbestos. Both are cheaper than Teflon and can be used over a largerrange of temperatures. Also, they will seal better if the stem is roughened with wear.Rope type packing is also easier to change during maintenance. However, it usuallyneeds a lubricator to work well.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 7/18


LANTERN RINGS AND LUBRICATORS

Figure PT-3 Valve Stem Packing with Lantern Ring and Lubricator

Figure PT-3 shows valve stem packing with a lantern ring and lubricator. Thelantern ring is made of metal with holes in it. it allows a lubricating compound to beforced into the space between the ring and the stem. The lubricating compound isusually silicon grease. It is used to ensure there is no sticking as the valve stemmoves up and down. To fill a lubricator, remove the lubricator nut and fill thelubricator with grease. Open the isolating valve and turn the replaced lubricator nutto force the grease into the system. You will know that there is enough grease in thelantern ring when the lubricator nut starts to tighten. Remember to close the

isolation valve when you recharge the lubricator. Leave the valve open when yourecharge the lantern ring.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 8/18


1.3 PACKING REPLACEMENT

1.3.1 Removing Old Packing

The most common sign of packing damage is too much leakage from the gland. Ifyou can't control this leakage by adjusting the gland follower, then the packingshould be replaced.

Before the packing in a valve can be replaced, the valve must be locked off usingthe platform's usual procedures. Next you must check manufacturer's specificationsto make sure that the old packing is replaced with packing of the right size and type.Then you must carry out the following procedures.

Loosen the gland follower nuts.

b) Swing open the gland follower dog bolts.

c) Open (or remove for a split type) the gland follower.

d) Remove the first few packing rings. The easy way is to use a packing tool.This works exactly like a corkscrew.

e) Take care not to scratch the shaft with the packing tool.

f) If there is a lantern ring, remove this with a piece of wire bent into a hook.

g) Remove the remaining packing rings.

h) Make sure all packing scraps have been removed.

i) Check the old packing and the shaft to see if it is only worn, or if there is amore serious reason for the leakage.

1.3.2 Installing New Packing

a) Make sure that the exposed portion of the shaft is completely clean. It is

important to get rid of all the grit particles so that they do not get pushed intothe stuffing box with the new packing.

b) Clean the shaft and stuffing box with a non-flammable, non-toxic solvent.

c) Brush down and then wipe the area with a clean rag.

d) If no manufacturer's information is available, measure the gap between theshaft and the stuffing box.

e) Similarly, measure the depth of the stuffing box.

f) Measure the thickness of the lantern ring.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 9/18


g) Calculate how many rings will be required. h) Find a suitable mandrel (thesame diameter as the shaft).

h) Wind the packing material round the mandrel as many times as the numberof rings required.

i) Cut the rings with a sharp knife.

k) Check how many rings you need to put below the lantern ring. The correctnumber must be replaced, otherwise the lantern ring will not be in line withthe lubricator.

l) Lubricate the rings with an anti-seize compound, so they will go in moreeasily.

m) Insert the packing rings and lantern ring one by one, pushing them into thestuffing box as far as they can go.

n) The joints of the rings should be staggered and cut on a slant as shownbelow.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 10/18


PERFORMING A PRESSURE TEST

A pressure test is carried out to find out if the packing has made a good seal around

the stem. If the valve is a "gate valve" the seal must be perfect at the ratedpressure. Most valves in the industry are rated using the American NationalStandards Institute (ANSI) code in psi. This rating is usually stamped on the valve;for example, 600. This means the valve has a maximum rated pressure of 600 psi.

Control valves however, may be allowed to pass a small amount of process fluid asthey move up and down. This amount depends on the valve and its position in theplant.

To make it easier to complete this task in the workshop, a gate valve is used toshow how to re-pack a stuffing box and how to do a pressure test. Both proceduresare also done on a control valve, with the actuator removed.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 11/18


Figure PT-4 Pressure Testing a Gate Valve

Figure PT-4 shows the layout for pressure testing a "gate valve". The outlet is

sealed off with a 'blanking plate. The inlet is connected to a pressure test rig.

Water is used as the pressurising liquid. The hand pump is operated until the testgauge shows the maximum working pressure of the valve. If the valve leaks throughthe packing, open the depressurising valve and tighten the packing. Repeat thepressure test. If the valve still leaks through the packing, depressurise the valve andreplace the packing.

Note: If the valve does not leak when fully open you can be sure it will not leakfully closed. This is because there is less force on the packing when thevalve is closed.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 12/18


PRACTICAL TASK 2

2.1 OBJECTIVES

OVERHAUL CONTROL VALVE.

The student will :

1 ) Remove the actuator from the valve body.

2) Completely dismantle (take apart) the valve.

3) Inspect all parts for wear and damage.

4) Reassemble (put back together) the valve.

5) Re-pack the gland and carry out a pressure test.

6) Completely dismantle the control valve actuator.

7) Inspect all parts for wear and damage.

8) Reassemble the control valve actuator.

9) Refit the control valve actuator to the valve body.

10) Set the control valve stroke using the attached instructions.

11) Carry out a leak rate test on the complete control valve assembly using theattached instructions.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 13/18


Note: There is a class 6 which defines leakage for very tight shut off. This testrequires air or nitrogen to be used as the test fluid. The leakage rate isgiven in bubbles of gas through water per minute. Checking this class is

not practical in a normal instrument workshop.

A P & ID may indicate a control valve must be "Tight Shut Off" (TSO). How tight thisshut off is depends on the design engineer, but class 5 and class 6 are usuallyconsidered tight shut off.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 14/18


LEAK TEST PROCEDURE

Figure PT-5 Leak Test

Use the workshop equipment supplied and connect the pressure test rig to the valveinlet. Connect the outlet to a measuring vessel. Connect an air supply to theactuator signal input. Figure PT-5 shows a block diagram of the leak testarrangement. Test as follows.

1. If the control valve assembly is air to close, apply 15 psi to the actuator tofully close the valve

2. If the control valve assembly is air to open, apply 3 psi to the actuator, tofully close the valve.

3. Operate the pressure test rig to apply 50 psi to the valve inlet . Time the rateat which water is collected in the measuring vessel (litres per min).

4. Use figures given -by the instructor to work out if the valve is serviceable.

5. TSO valves may be checked for leakage using air. In this case the numberof bubbles passing through the water in the measuring vessel gives theleakage rate, e.g. 10 bubbles per minute.

Note: Most of the CDC valves are made by "Fisher" and are standard class 2.The rated capacity depends on the size of the valve and the way it ismade. It is calculated using manufacturers tables.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 15/18


LAPPING

How well a control valve is seated when it is fully closed, depends on the metal tometal seal between the plug and the seat.

The above diagram shows a simplified, metal to metal seal. The plug is forcedagainst the seal by the actuator. The metal to metal seal can be worn away duringuse because of corrosion, cavitation, sand, etc. After a time the valve leaks badlywhen fully closed. The seal can be restored in the workshop using a techniquecalled "lapping". A grinding paste is applied between the plug and the seat. Then,the plug is rotated against the seat. This action smoothes the surface of the plugand seat so that the metal to metal seal is restored. The process can take a longtime, particularly with big valves. Some instrument workshops use electric lappingmachines to rotate the plug against the seat.

The actual process of lapping is difficult to describe so the instructor willdemonstrate "lapping" a valve.

If a valve fails its leak test then "lapping" is done and then the leak test is carried outagain.

It may be impossible to improve the valve seal by lapping. If this happens the seatand plug must be replaced.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 16/18


SETTING UP A CONTROL VALVE ASSEMBLY

There is a plate on the yoke of the actuator. This tells you the operating range of

the valve and the diaphragm pressure needed to make the stem do its full travel,(called the valve stroke).

Most modern valves will give these figures for both workshop and field operation asthe valves are balanced. Non-balanced valves however, will give two stroke ranges.One is an operating range when in the field, under full operating pressure, (e.g.3-15 psi). The other is the range for a "bench test". This range is used when you setup a valve on a bench in the workshop. The range allows for the unbalanced forceswhich occur in the field. A typical example of a bench test range would be 5-15 psi.This would give a field operating range of 3-15 psi

The "bench" setting of a control valve assembly can also be done for "split range"

operation. Normally a special range spring is fitted. The actuator is then adjusted sothat the stroke is completed over a diaphragm pressure range of for example, 3-9psi or 9-15 psi.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 17/18


CALIBRATION PROCEDURES

1 ) Use a calibration standard to see how much pressure is applied to the

actuator.

2) If the valve opens on air failure, the travel indicator should show the valve tobe closed when full loading pressure is applied. The valve should be openwhen no pressure is applied to the diaphragm case. If the travel indicatordoes not show this, then you should loosen the travel indicator screws andshaft until it does.

3) Vary the pressure on the diaphragm case over its full range and observe thevalve travel. Make sure that the valve plug is seated on the seat rings. If thetravel is not correct, it can be changed by screwing the valve plug stem intoor out of the stem connector. Use a wrench on the stem locknuts to turn the

stem. Do not turn the stem when the valve plug is on the seat. When thetravel is set properly, lock the stem locknuts against the stem connector andtighten the cap screws in the stem connector.

4) If travel starts at a pressure lower or higher than the required pressure, thenyou can adjust it by turning the spring adjuster. Turning the spring adjustercounterclockwise will decrease the spring compression. This causes thevalve travel to start at a lower loading pressure. Turning the spring adjusterclockwise will increase the compression on the spring. This causes travel tostart at a higher loading pressure. For a 0.2 to 1 bar diaphragm pressurerange, the valve should start travelling at 0.2 bar pressure.

5) When the control valve is installed and connected to the controller, it shouldbe checked again. You must check for correct travel, freedom from frictionand correct action, air to open, to match the controlling instrument. In orderto work properly the actuator stem and valve -plug stem must move freelywhen the loading pressure on the diaphragm is changed.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

Page 18/18


PRACTICAL TASK 3

3.1 SOLDERING

3.2 INTRODUCTION

SOLDERING AND WIRE WRAPPING

The older methods of soldering connectors onto cables are not used any more andare normally banned on oil/gas installations. All cables are joined to connectors bycrimping, the method practised during instrument craft practice.

However, you may need to do basic soldering of components onto a printed circuit(P.C.) board. This is the type of soldering that will be practised in this task.

3.3 GOOD P.C. BOARD SOLDERING

The P.C. board consists of copper conducting strips stuck onto an insulation board.The component is fitted onto the board using holes already drilled by the boardmanufacturer. The only connection between the component and the copper strip isthe solder which is applied. A well soldered joint (low resistance connection) and abadly soldered joint (high resistance connections) are shown in the diagram below.

M o

d u

l e

N o .

7 :

I n s

t r u m e n

t w o r k s

h o

p

U n

i t N o .

1 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 8

P & ID’s






UNIT 1 GENERAL SYMBOLS

UNIT 2 READING A P & ID


M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 GENERAL SYMBOLS FOR VESSELS, PUMPS, COMPRESSORS

AND TANKS 5

1.3 GENERAL PIPING AND INSTRUMENT LINES 7

1.4 GENERAL SYMBOLS FOR FIELD DEVICES 8

1.5 INSTRUMENT 12

1.5.1 Instrument Symbol Examples 14

1.6 COMPUTER SYMBOLS 16

1.7 PIPELINE DESIGNATION 18

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s







• Recognise the general symbols used for valves and actuators.

• Recognise the general symbols used for vessels, pumps, compressors andtanks.

• Recognise the general symbols used for field devices, e.g. orifice plates,filters, Venturis etc.

• Recognise the general symbols used for piping and instrument signal lines.

• Describe the letter symbols which indicate a particular instrument.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.1 INTRODUCTION

Piping and instrumentation diagrams show the instrumentation which is fitted to aparticular plant. These diagrams may contain only two or three sheets of paper ormany hundreds. They must be used when any plant maintenance work is carriedout. Unfortunately there is no standard method for P & ID's and only the basics ofthe system can be shown. This unit shows the general symbols.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.2 GENERAL SYMBOLS FOR VESSELS, PUMPS, COMPRESSORS AND TANKS

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.3 GENERAL PIPING AND INSTRUMENT LINES

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.4 GENERAL SYMBOLS FOR FIELD DEVICES

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





VALVES

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





The P & ID indicates the position of a control valve when the ESD is operated asfollows.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





Note : The symbol for manual operation is:

Most P & ID's only indicate the manual operation of important process valves. Othermanual valves e.g. drain valves, bypass valves, instrument block valves etc. do nothave the manual symbol.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.5 INSTRUMENT SYMBOLS

The instruments fitted into a control loop on a P & ID are shown by a circle. Lettersand numbers are written inside the circle to show the function of the instrument andits identification (tag) number. The first letter indicates the process variable beingmeasured and the following letters indicate what it does (function). Normally themaximum number of letters is 4.

All instruments in the same loop i.e. transmitter, controller and control valve, havethe same tag number.

The letters used on a P & ID diagram to show the operation of an instrument are notalways the same in every diagram.

Table 1 shows a list of common letters and their meanings. Lines are drawn in thecircle to show the instrument's position in the plant as follows :

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





TABLE 1

COMMON INSTRUMENT IDENTIFICATION LETTERS

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.5.1 Instrument Symbol Examples

All these instruments are on control loop 101 -

2. Alarms are drawn with the level high or low either inside the circle or outside. Theexample shows a temperature alarm high.

Shut down alarms are indicated using two letters for high or low, e.g.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





Some alarms indicate both high and low eg.

3. Motor operated valves have their position shown by a position switch. Thecontrol room indicator shows open or closed. This is drawn as follows :

Z for Position

S for Switch

I for Indicator

O for Open

C for Closed

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.6 COMPUTER SYMBOLS

Modern control systems are controlled by computers (microprocessors). Therecorders, indicators, alarms etc. are displays on a video screen. The controllerfunction is part of the microprocessor. To indicate this on a P & ID, it is usual to putthe circles in a square box. e.g.

Some computer operations are done separately from the computer control system.This is shown by using the circle symbol with the computer function written outside,for example:

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





The following computer symbols are reasonably standard.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s





1.7 PIPELINE DESIGNATION

Piping on a P & ID is indicated by :

1 ) Usage: For example, process, drain, nitrogen, blowdown, etc.

2) Line Number: The identification number of the line on the plant.

3) Size: Usually in inches.

4) Piping Class: The piping specification, both material and pressure rating.

The specification is usually given using American standards e.g. American Societyof Mechanical Engineers (ASME). or American Petroleum Institute (API).

Each installation uses slightly different methods to do this but the end result is thesame. A typical example is given below.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

1 -

G e n e r a

l s y m b

o l s









M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 WHAT'S ON A P & ID 4

2.3 EXAMPLE 1 5

2.3.1 Process Description 5

2.3.2 Instrumentation 6

2.3.3 Safety System 8

2.3.4 Operator's Aids 8

2.4 EXAMPLE 2 11

2.4.1 Process Description 11

2.4.2 Instrumentation 11

2.4.3 Safety Instrumentation 12

2.4.4 Operator's Aids 13

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s







• Understand P & ID for an operating company which he has not seen before.

• Get a 70% pass in a test on the understanding of a sight unseen operatingcompany P & ID.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





2.1 INTRODUCTION

Reading a P & ID is difficult and requires practice. Companies use differentmethods for making their diagrams.

This course is an introduction to reading a P & ID. You will have to learn the P & lDsfor any particular plant on the job.

The P & lDs on the job site have a 'legend'. The legend is a table which tells youexactly what all the symbols mean. You must study this table before you try to readthe P & ID.

2.2 WHAT'S ON A P & ID

The following gives a general outline of what you will see on a P & 1 D.

1. A layout of the process equipment, e.g. vessels, pumps, heat exchangersetc. A description of the pressure, flow rate, size etc. of the main parts.

2. All the pipelines fitted to the process equipment. Each line has a code on itto show its specification, size etc.

3. All the instrumentation fitted to the vessels, e.g. transmitters, controllers,control valves, relief valves etc.

4. Signal lines to and from the instrumentation.

5. All control loops should be complete. The diagram should show where theinstrument is, e.g. control room or field.

6. A P & ID is only a drawing of the process. The actual position of theinstrumentation may not be correct. Sometimes there is a note on thedrawing to tell you where the instrument is actually placed.

The example P & ID only shows one part of the plant. There are many P & ID's toshow all of a plant. Each P & ID tells you what other drawing you must look at to

learn about the next part of the process

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





2.3 EXAMPLE 1

Figure 2-1 shows a typical P & ID from a plant. The legend for this P & ID is alsogiven (page 10). Remember this legend only applies to this P & ID. Other P & ID'suse different symbols.

With reference to the P & ID.

1. The code number for the drawing is 062-Dl 12. It shows the piping andinstrumentation for vessel 5C-1 64 and pump 5G-1 55.

2. Vessel 5C-164 is a Propane/ADIP settler. It's size is 3 500 mm in diameter(0) and 10 500 mm T/T in length.

3. Pump 5G-155 is a lean ADIP recycle pump. It has a capacity of 122 m3

/h.

Note : T/T means tangent to tangent

2.3.1 Process Description

The vessel is used to separate propane from ADIP (AmineDiIsoPropanol). ThePropane/ADIP mixture is used to remove sulphur compounds from gases producedin the oil field.

The input to the vessel is from vessel 5C-1630 (Propane/ADIP mixer) on pipe lineP-55211 -10"-EA 2DX, shown on P & ID drawing 05-AD-1054

The outlets are:

Propane from the top of the tank to 5C-180 on drawing 05-AD-1054.

ADIP drained from the bottom of the tank to 5C-156 on drawing 062-D110.

The main process flow is shown by the thick black lines. All other lines aresecondary to the process.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





2.3.2 Instrumentation

•

LOOP 803

Loop 803 is the only control loop on the diagram (area A). It is a pneumaticcontrol loop. It keeps the interface level between the propane and the ADIPconstant (the interface level is the level at which the propane and the ADIPmeet).

The loop consists of:

Level transmitter (LT 803). This is of the differential pressure type with apneumatic signal output.

Level switch low (LSL 803). This is mounted behind the control panel.

Level alarm low (LAL 803). This is an indicating light mounted on the front ofthe control panel.

Level switch high (LSH 803) behind the control panel.

Level alarm high (LAH 803) indicating light on the control panel.

Level recorder (LR 803) on the control panel. The recorder is a three penunit which combines LR 803 and FIR 789 (2 readings).

The level indicator controller (LIC 803) is of the pneumatic type. It ismounted on the control panel.

The control valve is a globe valve with a pneumatic diaphragm (LV 803).

• LOOP 804

Loop 804 is a shut down loop for both the pump and the control valve (LV803). It operates when the interface level reaches the low low point. Thelevel is measured using a displacer type pneumatic transmitter (LT 804).The level controller low low is an on/off controller (LCLL 804 and LCLL

804A). LCLL 804 switches off the pump and closes LV 803 when theinterface level falls below 500 mm. LCLL 804A switches the system on(reset) when the interface level rises to 650 mm.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





A time delay is fitted in the pump motor control line to allow the valve tomove before the pump starts or stops (note 1).

The pneumatic signals operate pressure switches. The switches sendelectrical control signals to the pump motor and LCV 803 solenoid operatedvalve (SOV 803).

When the low low level is reached SOV 803 de-energises. This breaks theair signal to the actuator diaphragm and the valve closes. ESD HS-042/1(Drawing 05-AD-1063) is also connected into the circuit. If the ESD ispressed, the pump stops and LV 803 closes. (The valve is fail closed (FC)).

• LOOP 1812

This loop indicates to the operator in the control room the differentialpressure across HV 1816. HV 1816 is a gate valve on the propane outletline.

The loop consists of :

Electrical pressure differential transmitter (PDT 1812) with a locally mountedindicator (PDI 1812/2).

Pressure differential indicator in the control room (PDI 1812/1). This iscombined with temperature indicator (TI 666) into one unit.

Pressure differential switch high (PDSH 1812) behind the control panel.

Pressure differential alarm high (PDAH 1812) on the control panel.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





2.3.3 Safety System

The inlet to the vessel (5C-164) and the propane outlet from the vessel arecontrolled by pneumatically operated ball valves, set by hand.

HV 1841 inlet.

HV 1842 outlet.

Both these valves fail closed (FC) with tight shut off (TSO) if the ESD system isoperated. The ESD operates on SOV which breaks the air supply to the valve forshutdown. ESD reset is done by hand in the field (HS 1841 and HS 1842).

The pressure safety valve (PSV 948) prevents the pressure in the vessel reaching a

dangerous level. It vents the vessel to the HP (high pressure) flare header (line VF-71556-10"-EA28) and to the flare, where it is burnt. The PSV is set to operate at 20barg.

2.3.4 Operator's Aids

A sight glass is fitted to the vessel (LG 947).

A pressure gauge (PG 949) is fitted to the discharge of the Lean ADIP RecyclingPump.

An orifice plate and pneumatic flow transmitter are fitted in the ADIP outlet line. Theflow transmitter's signals are used to record the ADIP flow rate in the control room.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





2.4 EXAMPLE 2

Figure 2-2 shows a simplified P & ]D from a more modern plant. In this plant thecontrol is done using a distributed control system with microprocessors. Thedrawing uses the same symbols as introduced in Unit 1. You should look at this unitif you don't remember the general symbols.

2.4.1 Process Description

The Sweet Gas K.O. (knock out) Drum is used to separate gas/condensate/water.The input fluid stream comes from vessel 32V-101. The vessel is fitted with a mistextractor pad and a vortex breaker. It produces three outputs.

1. Treated gas comes out of the top of the vessel. It goes to dehydration (waterremoval) vessel 42E-309

This is shown on drawing 42.00.30.022

2. Water comes out of the bottom of the vessel. It goes to vessel 32V-184.


3. Condensate (hydrocarbons) comes of the middle of the vessel. It goes tovessel H.P. separator 32V-22


2.4.2 Instrumentation

The basic control of the vessel is done using two level indicating controllers; LIC2819 and LIC 2823.

• LOOP 2823

This is the main level control loop for the vessel. It maintains the gas/liquidlevel in the drum. The level transmitter (LT 2823) is of the D/P type (4-20mA)and provides an electrical signal to LIC 2823. This is a computer function inthe control microprocessor. The high alarm (LAH set at 4450 mm) and lowalarm (LAL set at 588 mm) are indicated on the VDU display in the controlroom. The control microprocessor provides an electrical signal (4-20mA) toset the position of the control valve (LV 2823). The control valve ispneumatically operated. The conversion from an electrical to a pneumaticsignal is done using an I/P converter LY 2823. LIC 2823 sends an internaldata signal to a level compute unit inside the microprocessor. This unitcloses the interface loop 2819 if the liquid level in the tank falls below 1800

mm. If this operates, a low alarm (LAL 2823) is indicated on the control roomVDU.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





• LOOP 2819

This loop controls the interface level between the hydrocarbons and the

water. The system uses on/off control. If the level fails below 589 mm LIC2819 closes the valve. LIC 2819 reopens the valve when the level risesabove 988 mm. There is a connection inside the microprocessor whichcloses the valve if the liquid level falls below 1 800 mm. A switch (LZSC2819) on LV 2819 is used to indicate the position of the valve. It indicatesclosed on the control room VDU (LZAC 2819).

• FLOW MEASUREMENT

The collection of instruments in area A shows the modern computer measurementof flow rate and total flow. It consists of

a) Temperature Transmitter TT 5886

b) Pressure Transmitter PT 3996

c) Two Flow Transmitters FT 1988A and FT 1988B

The signals from these transmitters are connected to the microprocessor. Themicroprocessor internally works out the gas flow rate and total flow in standard units(Nm

3 hr and N m

3). Temperature (TI 5886), pressure (PI 3996) flow (FI 1998) and

total flow (FQI 1998) are all indicated on the control room VDU.

Note : Two flow transmitters are used to make the system more reliable. If one FTfails the other still provides a signal. The microprocessor will indicatetransmitter failure.

2.4.3 Safety Instrumentation

The ESD system is applied via a computer <L2> which ensures XV 9829 and XV9887 close when the ESD is operated. <L2> provides a signal to solenoid operatedthree way valves. If the ESD is operated the signal to the solenoid valves isremoved. The three way valve vents the air supply to the piston actuator and the

valve closes. A mechanical type pressure safety valve is fitted (PSV 8005). Thisreleases the gas to the flare if the pressure in the vessel exceeds 75 bar g.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





2.4.4 Operator's Aids

A sight glass (LG 2828) indicates the hydrocarbon/water interface. Level sight glass

(LG 2822) indicates the liquid level in the vessel. This is made from three separatesight glasses to cover the distance required. A typical layout is given in Figure 2-3.

Figure 2-3 Combination Sight glass

Note : The flow through the vessel is controlled from the previous vessel ondiagram 32.00.30.001. The control valve (FV 1821) has pneumaticdiaphragm type actuator. It is operated by an I/P converter (FY 1821). Thevalve is designed to fail locked (intermediate). This means , that the loss ofthe control signal will not stop operations immediately.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s





M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

2 -

R e a

d i n g

P & I D

’ s









M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 5

3.3 PRACTICAL TASK 1 7

3.4 PRACTICAL TASK 2 15

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s






The student will complete the following practical tasks on reading a P & I D.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





3.1 INTRODUCTION

The following two practical tasks have been given for you to practice reading a P &

ID.

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





3.2 PRACTICAL TASK 1

With reference to drawing 062-D110 (page 4), complete the following tasks.

1) Using a coloured pencil, outline the main process flow lines.

2) The size of the input feed drum

3) The size of the ADIP absorber

The purpose of the ADIP absorber is to remove the sulphur compound hydrogensulphide from the untreated DEO (De-Ethaniser Overheads), mostly methane gas.The gas moves up the absorber, as the lean (clean) ADIP moves down. The clean ADIP removes the sulphur compounds from the gas and leaves the bottom as rich

(dirty) ADIP.

4) The treated gas goes to

----------------------------------------------------------------------------------------------------

5) The dirty ADIP goes to

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





6) Name each instrument in flow loop 785

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

7) When would you expect FV 785 to open.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





8) Name each instrument in loop 1844.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

9) What does loop 1844 do?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

10) What are PSV 925A and PSV 925B?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





11) What does the interlock between PSV 925A and PSV 925B do.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

12) How many interconnected sight glasses are there for LG 923?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

13) Name each instrument in loop 781 and say where they are mounted.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





14) What does LCLL 782 do?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

15) What is PDT 783 for?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

16) What does the symbol below mean?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





17) What does the symbol below mean in a vessel?

18) What does the symbol below mean in a vessel?

19) What are the following?

P - 55200 - 10" - EA2D

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





20) Where do the semi - lean and lean ADIP's come from?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





3.3 PRACTICAL TASK 2

INTRODUCTION

The previous task used a P & ID produced by Kellogg. This task uses a P & IDproduced by Bechtel-Technip. This is done so that you can see that althoughconstruction companies follow the same basic rules for P & ID, each P & ID is a littledifferent.

BASIC PROCESS DESCRIPTION

The P & ID 24-00-30016 (see page 13) shows the 2nd stage of a two stagecentrifugal gas compressor. At this stage, the process is controlled by an anti-surgecontroller. Using a microprocessor, the anti-surge controller controls flow throughand the pressure increase across the stage.

The product of flow and pressure increases (AP) must stay constant. If it does notstay constant then surge occurs. (Surge means the rotor of the compressor movesbackwards and forwards). Surge can badly damage the compressor.

The output of the anti-surge controller adjusts the position of the recycle valve. Thisvalve allows the compressed gas to flow back to the input of the stage. (This gasreturns to the input via a cooler and suction scrubber (KO. drum)). This recycledgas increases the flow through the stage and reduces the differential pressureacross it. This stops the surge.

1 ) What does UIC mean for the anti-surge controller?

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

2) Write down the inputs to UIC 1632

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





3) The number of the re-cycle valve is:

-------------------------------------------------------------------------------------------------

4) Describe loop 1638.

-------------------------------------------------------------------------------------------------

5) What is TG 6611 and where is it?

-------------------------------------------------------------------------------------------------

6) Where is TI 5641 ? When will the alarm light?

-------------------------------------------------------------------------------------------------

7) What happens if TAHH 5842 lights?

-------------------------------------------------------------------------------------------------

8) If PAL 3842 is light, what can you do?

-------------------------------------------------------------------------------------------------

9) What is PDG 4838 for?

-------------------------------------------------------------------------------------------------

10) What pressure are the mechanical pressure safely valves set at?

-------------------------------------------------------------------------------------------------

11) Where does the gas go if the ESD opens the compressor depressuring line?

-------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s





12) What do the letters "HVSO" and "HZLO" mean?

-------------------------------------------------------------------------------------------------

13) How are the two anti surge controllers inter-connected?

-------------------------------------------------------------------------------------------------

14) Explain Note 1:

-------------------------------------------------------------------------------------------------

15) Where does the discharged gas go?

-------------------------------------------------------------------------------------------------

16) What is the average increase in pressure across this stage?

-------------------------------------------------------------------------------------------------

17) What is the size of the suction line?

-------------------------------------------------------------------------------------------------

18) What is the size of the discharge line?

-------------------------------------------------------------------------------------------------

19) Why is the discharge line smaller?

-------------------------------------------------------------------------------------------------

20) What is meant by Nm3 /h?

-------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

8 :

P & I D ’ s

U n

i t N o .

3 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 9

CONTROL SYSTEM 1



July 1999- Rev.0






UNIT 1 COURSE INTRODUCTION


M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 BASIC THEORY 4


1.2.2 On/Off control 4

1.2.3 Manual Control 7

1.2.4 Automatic Flow Control 8

1.2.5 Temperature Control 9

1.2.6 Pressure Control 12

1.2.7 Centrifugal Pump Control 14

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n







• Use the Autodynamics simulator keyboard to adjust values on the videodisplay.

• Perform the following tasks on the simulator to demonstrate the use of thefollowing.

On/Off control

Hand control

Flow control

Temperature control

Pressure control

Pump control

Centrifugal pump

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





1.1 INTRODUCTION

The aim of this unit is to introduce the student to instrument control systems usingthe Autodynamics simulator.

1.2 BASIC THEORY

1.2.1 Introduction

The following theory is a back-up to the practical exercises carried out on the Autodynamics simulator.

1.2.2 On/Off control

On/Off control is the simplest form of control. The controller works between twolevels. It switches 'ON' at one level and it switches 'OFF' at the other. A simplediagram of the system is shown in Figure 1-1.

Figure 1-1 Simple On/Off Control

On/Off control is shown on the simulator by a block valve. An example of the blockvalve is the gate valve. It is either open (on) or closed (off).

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





Figure 1-2a shows the graphic display seen on the video display unit (VDU).This, isthe operator's Process Flow Diagram (PFD). The P & ID to match the PFD is also

given.

Figure 1-2b P & ID

Figure 1-2 ON/OFF Process Control

The instrumentation provided for ON/OFF flow control is:

1. Inlet (upstream) pressure by loop 111. Indication on the workstation VDU.

2. Flow rate by loop 101. Indication on the workstation VDU.

3. Outlet (downstream) pressure by loop 113. Indication on the workstationVDU.

4. Pressure loop 112 is added to show pressure loss across the block valve.The pressure loss is the indication on loop 111 minus the indication on loop112.

5. The position of block valve (HV-131) is indicated as open or closed on theworkstation VDU.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





CORRECT LOOP OPERATION

OFF(closed): FIR reads zero.ZI 131 indicates closed.PT 112 and PT 113 read 129 kg /cm

2

ON (Open): FR 101 reads 125 TPHPI 111 reads 146.4 4 kg/ cm

2

ZI 131 indicates openPI 112 reads 144.4 kg / cm

2

PT 113 reads 129 kg / cm2

The correct 'OPEN' 2 position shows the downstream (outlet) pressure fixed at 129

kg/cm . At this pressure, the flow rate for a differential pressure of 146.4-129 (17.4kg cm

2) is 125 TPH.

The correct pressure loss across the valve is 2 kg / cm2 (146.4-144.4). If the

pressure loss across the valve is higher than this it means there is a fault. The valveis not fully open or it's in bad condition. It needs maintenance work.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





1.2.3 Manual Control

Figure 1-3a shows the process flow diagram seen on the VDU for manual control.

The matching P & ID is shown in Figure 1-3b. The operator can use the keyboard toopen and close the control valve manually. In this way the operator can set therequired flow rate.

Figure 1-3 Manual Control

The instrumentation provided for the manual flow control is :

1. Inlet (upstream) pressure by loop 211. Indication on the workstation VDU set at146.4 kg/ cm

2.

2. Flow rate by loop 201. Indication on the workstation VDU.

3. Piston operated control valve FCV 231. The position of FCV 231 is set in thecontrol room by HC 231.

4. Loop 212 indicates the outlet pressure from the control valve.

5. Loop 213 indicates the downstream pressure (set at 129 kg/ cm2).

CORRECT LOOP OPERATION_

The upstream pressure is fixed at 146.4 kg/ cm2. The downstream pressure is fixed

at 129 kg/ cm2. The operator controls the flow by adjusting HC 231. The throttling

effect of the control valve is shown by the difference in pressure between loops 211and 212 on either side of the control valve. Remember that when the control valveis closed PI 212 will show the downstream pressure at 129.0 kg / cm

2.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





1.2.4 Automatic Flow Control

INTRODUCTION

The flow of liquid is automatically controlled using a Flow Indicating RecorderController (FIRC). The control actions (PID) are set to give good control. High andlow alarms are set at 150 TPH and 50 TPH. Figure 1-4 gives the PFD and the P &ID for the system.

Figure 1-4b P & ID

Figure 1-4 Automatic Control using an FIRC

The FIRC will control at a designed flow rate of 129 TPH. The upstream anddownstream pressures are fixed at 146.4 kg/ cm

2 and 129.0 kg/ cm

2 . The control

valve is 60% open.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





1.2.5 Temperature Control

The simulator is designed to show temperature control using an industrial shell/tube

heat exchanger. You will see many of these in use throughout operatingcompanies.

THE SHELL/TUBE HEAT EXCHANGER

Figure 1-5 Shell/Tube Heat Exchanger

Figure 1-5 shows an example of a shell/tube heat exchanger. The cooling fluidflows round inside the tubes and the process fluid flows outside the tubes inside theshell.

The cooling fluid takes heat from the process fluid as it passes through the tube.So, the process fluid is cooled. The amount of cooling depends on four factors:

1. The rate of flow of the cooling fluid.

2. The rate of flow of the process fluid.

3. The initial temperature of the cooling fluid.

4. The initial temperature of the process fluid.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





SIMULATOR PFD AND P&ID 70.6

Figure 1-6b Heat Exchanger P & ID

Figure 1-6a Heat Exchanger PFD

Figure 1-6 Temperature Control (Shell-Tube Exchanger)

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





CONTROL PRINCIPLES

The operating conditions for the heat exchanger are as follows :

Coolant flow rate 104.2 TPH with an inlet temperature of 25°'C and an outlet

temperature of 70.6°C.

Process fluid flow rate 150 TPH with an inlet temperature of 180°C and an outlet

temperature of 116.7°C (temperature reduction of 63.3°C)

The controlled variable is temperature of the process fluid at the outlet. This ismaintained by a TIRC (Temperature Indicator Recorder Controller). The TIRCoperates the 3-way valve (TCV-624). This allows some of the hot process fluid tobypass the system.

The mixture of cooled process fluid and bypass hot process fluid keeps the outputprocess fluid at a constant 116.7°C.

Two operator alarms are added.

Low coolant flow rate. The alarm operates if the coolant flow falls below 10 TPH

There is a high/low temperature alarm at the process fluid outlet. The high alarm

operates at 150°C, and the low alarm at 90°C.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





1.2.6 Pressure Control

INTRODUCTION

The simulation of pressure control is done using an expansion vessel. The principleof operation is 'BOYLE's LAW' (at a constant temperature Pressure x Volume =Constant). This means that when the volume increases the pressure must fall.Figure 1-7 shows the PFD and P & ID for simulator pressure control.

Figure 1-7a Pressure Control PFD

Figure 1-7 Pressure Control

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





CONTROL DESIGN

For correct operation the inlet pressure of the process gas falls as it expands in the

vessel from 15.5 kg / cm

2

to an outlet pressure of 4 kg / cm

2

. The flow rate is fixedat 10.2 TPH. The system is controlled by PIRC-712. This positions the outletpressure control valve in order to maintain the set-point pressure in the vessel.

OPERATOR ALARMS

These are set as follows :

Inlet flow

High alarm above 13.2 TPH

Low alarm below 2 TPH

Outlet pressure

High alarm above 14 kg,/ cm2

Pressure safety valve (PSV-710) is set at 15 k g/ cm2

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





1.2.7 Centrifugal Pump Control

INTRODUCTION

The centrifugal pump is a common oil field device used to move liquids. It can sendoil from an offshore platform, via a pipeline, to a refinery. It can also pump oil onto atanker etc.

• Principle of operation

Figure 1-8 The Simple Centrifugal Pump

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





Figure 1-8 shows a simple centrifugal pump.

Operation

1. Liquid enters through the hole at the centre (the eye).

2. The impeller rotates very fast.

3. The vanes on the impeller drive the liquid outwards (centrifugal force). Thevelocity of the liquid increases.

4. Drops of liquid fly off the ends of the vanes and hit the pump casing.

5. When the drops of liquid hit the pipe casing their kinetic energy is changedto pressure energy. The higher pressure of the drops forces the liquid out of

the outlet at a higher pressure.

6. The size of the pump depends on the mass flow rate and the gain in headpressure of the liquid as it passes through the pump.

7. Figure 1-9 shows a multi-stage impeller. Most large pumps use a multi-stageimpeller where the output of one impeller is the input to the eye of the next.

Figure 1-9 Multi-stage Impeller

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





SIMULATOR PFD AND P & ID

Figure 1-10 shows the simulator PFD of the centrifugal pump action as seen by the

operator on the workstation screen. It also shows the P & ID.

Figure 1-10a Centrifugal Pump PFD

Figure 1-10 Centrifugal Pump Control

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n





CONTROL OPERATION

1. Under normal operation, the level in the vessel (V-500) is constant. it

provides a suction pressure of 4.5 kg / cm

2

.

2. The normal flow rate is 125 TPH set by FIRC-502. The outlet (discharge)pressure is 18 kg / cm

2.

3. HCV-544 allows the liquid to return to the vessel (recycle line) so that thepump can be kept running even if FIRC-502 closes the outlet valve.

4. The minimum flow line reduces pump vibration which may occur when theflow rate is very low.

PROCESS ALARMS

1. Suction alarm low (PAL 511) which operates at below 0.8 kg/cm2

2. Discharge -pressure alarm low (PAL-512) which operates at below1.0 Kg/cm

2

3. Electric motor overcurrent alarm (IAH-551) which operates when the currentis above 325 A.

4. Discharge flow alarm low (FAL-501) which operates when the flow failsbelow 50 TPH.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

1 -

I n t r o

d u c t

i o n






UNIT 1 COURSE INTRODUCTION


M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





TABLE OF CONTENTS

Para Page

PRACTICAL TASK 1 3

PRACTICAL TASK 2 5

PRACTICAL TASK 3 13

PRACTICAL TASK 4 16

PRACTICAL TASK 5 18

PRACTICAL TASK 6 19

NOTES FOR INSTRUCTOR 20

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





PRACTICAL TASK 1

ON/OFF CONTROL

1) Make sure the Autodynamics simulator is operating as designed with thevalve open.

The screen VDU shows :

PI-111 reads 146.4 kg/cm2

FR-101 reads 125 TPHZI-131 reads Valve openPI-112 reads 144.4 kg/ cm

2

PI-113 reads 129 kg/ cm2

2) Close the valve manually using the keyboard.

3) Fill in the blanks.

ZI-131 reads ..............................PI-111 reads ..............................PI-112 reads ..............................PI-113 reads ..............................FR-101 reads ..............................

4) Open the valve. Does the VDU return to the normal operating position with

the valve open.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





5) Look at the screen. Describe what is happening.

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





PRACTICAL TASK 2

MANUAL CONTROL

PART 1

1) Make sure the autodynamics simulator is operating as designed with HCV-231 60% open.

The VDU screen shows :

PI-211 reads 146.4 kg/ cm2

FR-201 reads 96 TPH

HCV-231 reads 60%

PI-212 reads 130.4 kg/ cm2

PI-213 reads 129 kg/ cm2

2) Close the valve. The VDU screen shows :

PI-211 reads ..............................

FR-201 reads ..............................

HCV-231 reads ..............................

PI-212 reads ..............................

PI-213 reads ..............................

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





3) Open the valve in 10% steps to fully open (100%). Fill in the table for eachstep.

%Open Flow Rate PI 212 PI 211-PI 212

10 0 129 17.4

20

30

40

50

60

70

80

90

100

4) Plot a graph of flow rate against value % open.

5) Plot a graph of pressure drop across the valve (PI 211 -PI 212) against valve% open.

6) Does the flow rate increase linearly with valve % open.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





7) Does the pressure drop across the valve decrease linearly as the valveopens.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

8) Do your results show that a control valve when fully open causes a much

larger pressure loss than the block valve used during practical task 1.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





VALUE % OPEN

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





PART 2

1) Return the manual control to its design position.

HCV-231 is 60% open.

2) Look at the screen. The upstream pressure has risen to 155 kg / cm2

. Adjust the HCV-231 so that the MV returns to a SP of 96 TPH.

The new setting of the valve is ……………………….% open.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





PRACTICAL TASK 3

AUTOMATIC FLOW CONTROL

1) Make sure the Autodynamics simulator is operating as designed.

The screen VDU shows :

PI-311 reads 146.4 kg/ cm2g

FIRC-301 reads 129.0 TPH

PR-312 reads 133.5 kg/cm2 g

PI-313 reads 129 kg/cm2 g

2) Put the flow controller into manual and open the valve.

The high alarm is set at ………………………..TPH.

With the flow controller still in manual close the valve.

The low alarm is set at ………………………….TPH.

3) Return the simulator to its designed operating condition in automatic.

4) Change the set point of FIRC-301 to 120 TPH (step change).

Time the fall in the measured value every 10 seconds until the new set pointis reached.

5) Complete the enclosed graph from the results you have obtained.

6) Could the response time be improved? Ask the instructor if he can changethe PID settings for a quicker response.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





VALUE % OPEN

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





PRACTICAL TASK 4

TEMPERATURE CONTROL

1) Make sure the Autodynamics simulator is operating as designed. The VDUscreen shows:

TI-623 reads 180.0 °C

FR-602 reads 150.0 TPH

FI-601 reads 104.2 TPH

TI-621 reads 25.0°C

TR-622 reads 70.6 °C

FI-603 reads 53.7 TPH

TR-625 reads 81.4°C

TIRC-624 reads 116.7°C

2) The following questions are to be answered by observation of the screen.The instructor will be simulating process changes to illustrate temperature

control

a) Why is the bypass flow rate rising?

------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------

b) Why is the bypass flow rate falling?

------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------

. ------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





c) What has happened? What could you do to correct the problem?

. ------------------------------------------------------------------------------------------

. ------------------------------------------------------------------------------------------

. ------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





PRACTICAL TASK 5

PRESSURE CONTROL

1) Make sure the Autodynamics simulator is operating as designed. The VDUscreen shows:

PI-711 reads 15.5 kg/ cm2 g


HCV-731 is 40% open

HV-731 is Open


PIRC-712 indicates 10 kg/cm2 g


2) Close HCV-731 slowly until the FAL-701 comes on.

The FAL-701 setting is ………………………….TPH.

Open HCV-731 slowly until the FAH-701 comes on.

The FAH-701 setting is ………………………..TPH.

Does the PIRC-712 maintain control over the range from FAH to FAL.

3) Return the simulator to its designed condition.

4) Close HV-732. Describe what happens.

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------

5) What is the setting of PSV-710 ?

---------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





PRACTICAL TASK 6

CENTRIFUGAL PUMP CONTROL

1) Make sure the Autodynamics simulator is operating as designed. The VDUscreen shows :

HCV --544 is closed

FIRC-502 reads 125 TPH


PR-511 reads 4.5 kg/cm2 g

HV-541 is open

HS-542 is on

II-551 reads 290 A

PR-512 reads 19 kg/cm2 g

HV-543 is open


2) Reduce the set point on FIRC until the FAL-501 comes on.

What is the minimum flow setting for Loop-501 ..................

If the FIRC-502 set point must be kept at this low flow level. How can wekeep the pump running correctly?

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

3) Return the simulator to its designed position. Open the recycle line valveHCV-544. Describe what happens.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s





NOTES FOR INSTRUCTOR

1 ON/OFF CONTROL

This task is given as an introduction to the Autodynamics simulator. Makesure that all students can operate the keyboard to change displays andmanipulate the opening and closing of the valve.

For student operation 5, the instructor will set the control desk so thatPI-1 11 increases to 155 kg/cm

2 with a ramp input set at 3.

2) MANUAL CONTROL

Make sure that all students can remember how to operate the keyboard tochange displays and manipulate the opening and closing of the valve.

For student operations in part 2 set the control desk so that PI 211 increasesto 155 kg/cm

2. Step increase is best.

3) FLOW CONTROL

Make sure that all students can remember how to operate the keyboard,change displays and manipulate the opening and closing of the valve.

To obtain a reasonable response time for the student operation 4, set thesimulator to 0.5 real time.

4) TEMPERATURE CONTROL

Make sure that all students can remember how to operate the keyboard,change displays and manipulate the opening and closing of the valve.

This is a task to find if the student understands basic control concepts.

For student operation 2(a), decrease the process flow rate.

For student operation 2(b), lower the inlet coolant temperature.

For student operation 2(c), increase the coolant inlet temperature to 35°C and thisprocess flow rate to 170 TPH.

5) PRESSURE AND PUMP CONTROL

Make sure that all students can remember how to operate the keyboard, changedisplays and manipulate the opening and closing of the valve.

These tasks are given so that the students can try basic manipulations of theprocess using the simulator keyboard. It is hoped they will understand

• The operation of the PSV at the high high level. Pressure control.

• The operation of the recycle valve to maintain low output flow rates. Pumpcontrol.

M o

d u

l e

N o .

9 :

C o n

t r o

l s y s

t e m s

1

U n

i t N o .

2 -

P r a c

t i c a

l T a

s k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 10

PROCESS CONTROL FUNDAMENTAL



July 1999- Rev.0

Page 1/14



UNIT 1 BASIC CONTROL THEORY

UNIT 2 TUNING A CONTROLLER

UNIT 3 INTRODUCTION TO DCS AND PLC

UNIT 4 HONEYWELL TDC 3000 DCS

UNIT 5 FOXBORO IA DCS


M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 2/14


TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 PROPORTIONAL CONTROL ACTION 4

1.3 INTEGRAL (RESET) CONTROL ACTION 6

1.4 DERIVATIVE (RATE) CONTROL ACTION 7

1.4.1 Old Type Controller 8

1.4.2 Modern DCS Controller 8

1.5 RATIO CONTROL 10

1.6 CASCADE CONTROL 11

1.7 FEED FORWARD CONTROL 12

1.8 MULTI-VARIABLE CONTROL 13

1.9 ADAPTIVE CONTROL 14

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 3/14




• Describe the use of proportional control.

• Describe the use of integral control.

• Describe the use of derivative control.

• Describe the use of combination (P plus I plus D) control

• Describe the use of cascade control.

• Describe the use of ratio control.

• Describe the use of feedforward control.

• Describe the use of adaptive control.

• Describe the use of multi-variable control.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 4/14


1.1 INTRODUCTION

The aim of this unit is to describe the use of proportional, integral and derivativecontrol. The course also introduces the newer methods of control; cascade, ratio,feedforward, adaptive and multi-variable.

1.2 PROPORTIONAL CONTROL ACTION

The basic continuous control mode is "proportional control". With proportionalcontrol the controller output is algebraically proportional to the error input signal tothe controller. The simple block diagram model of the controller shows this.

In this case the controller output is the gain of the controller (K) times the errorsignal (E), or

O/P = KE

This equation is called the control algorithm. The value of K can be set manually onolder pneumatic equipment. On modern DCS systems it is set using a computerprogramme.

The mechanism which adjusts the gain on many industrial controllers is expressedin terms of proportional band (PB). Proportional band is defined as the span ofvalues of the input which corresponds to a full or complete change in the output.This is usually expressed as a percentage and is related to proportional gain by:

In practice, wide bands (high percentages of PB) have low gain and narrow bandshave high gain. There are many ways to show the effects of varying proportionalband. One example is shown in Figure 1-1.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 5/14


Figure 1-1 Effect Of Proportional Control On Controller Output

Proportional control is quite simple. It is the easiest of the continuous control modesto tune, as there is only one value to adjust. It is very stable and responds quickly tochanges.

However, proportional control has one big disadvantage. At steady state, it shows"offset". This means there is a difference at steady state between the set point, (SP)and the actual value of the Measured Variable (MV).

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 6/14


1.3 INTEGRAL (RESET) CONTROL ACTION

Reset (integral) action provides a signal which depends on the size of the errorsignal. It is different from proportional control because it Will continue to cancel anyerror until the offset is zero.

Reset (integral) control action is combined with proportional control action. Thiscombination is called proportional-reset or proportional integral action (PI control).This combination provides a control action which is stable and responds quickly withno offset.

Figure 1-2 Proportional plus Reset Control Action

Figure 1-2 shows the action of P & I control. The rate at which integral action isapplied depends on the reset time adjustment. This is measured in either repeatsper minute or minutes per repeat, depending on the manufacturer. The simplediagram below is used to show what this means.

In the diagram above the reset action repeats the proportional action twice in oneminute. The reset time is thus either

2 repeats per minuteor 0.5 minutes per repeat.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 7/14


1.4 DERIVATIVE (RATE) CONTROL ACTION

Derivative (rate) control action produces an output signal which is proportional tohow fast the error signal changes (its rate). This type of control is only used whenthe loop response is very slow. Using derivative control on a loop which responds tochanges quickly is dangerous. The output moves too quickly to a maximum or aminimum and can produce shock waves in the process being controlled.

Derivative control action is only used with proportional and integral action. Together,the three control modes provide what is called a Proportional Integral Derivativecontrol action, (PID control).

Figure 1-3 shows the effect of PID control for a step change in the error signal.

Figure 1-3 The Output of a PID Controller

The output signal is a combination of the three control actions. Note that the rateadjustment changes how long the derivative signal is applied. Some manufacturerscall derivative action "pre-act" as it only produces a signal at the start to quicken theresponse time.

The older types of controller (e.g. Foxboro pneumatic type 43AP or SPEC 200analog electrical/electronic) combine the PID Control into a single unit whichoperates on the error signal. Modern microprocessor controllers, however use a lotof PlD control but in different way. The block diagrams below show the difference.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 8/14


1.4.1 Old Type Controller

The block diagram shows a typical older type PID controller. If the set point ischanged the derivative action can cause large and unstable changes in output. So,D is only used for very slow loops.

1.4.2 Modern DCS Controller

The block diagram shows a typical micro-processor based DCS controller. Thederivative action is only applied to changes in the measured value. Changes in theset point are not affected by the derivative action. This method provides a betterresponse to process changes and more accurate control. Note that the PID settingsare changed using a computer programme. This programme must have an"algorithm" of the controller characteristics.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 9/14


The table below gives a summary of the different types of control action available.

ON/OFF CONTROL.Inexpensive

Extremely simple

Excellent for control of large capacity (volume) systems.

Process variable cycles about set point.

Control valves are easily worn out.

Cannot be used for small capacity systems.

PROPORTIONAL.

Simple

Good for small capacities.

Stable when set up (tuned) correctly.

Rapid response.

Offset at steady state.

Easy to tune.

PROPORTIONAL plus RESET (P & D.:No offset

Better response time than reset alone

P & 1 can reduce the stability of the loop. The gain may need to be reduced when

reset is added.

PROPORTIONAL plus RESET plus RATE (PID).

Most complex

Most expensive

Rapid response

No offset

Difficult to tune

Best control if properly tuned.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 10/14


1.5 RATIO CONTROL

Ratio control is used when two fluids must be mixed together in a specific ratio. Apractical way to do this is to use a standard control system to control the flow onone line. The same transmitter signal is used as a set point for a second controllerwhich controls the flow in a second line. The ratio of one flow rate to the other canbe changed by adjusting the gain for proportional band) of the secondary controller.Figure 1-4 shows a typical ratio control system. The air to fuel ratio of the fluid goingto the combustion chamber is set at 2:1.

Figure 1-4 Ratio Control System

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 11/14


1.6 CASCADE CONTROL

Figure 1-5 is given as an example of cascade control. It shows a chemical mixingvessel. When the two chemicals are mixed they produce heat. Cooling water ispassed around the outside of the vessel via spray rings. This keeps the temperatureof the reaction constant. The temperature is kept constant using cascade control asfollows. The principle of cascade control is to use two controllers. A "master"controller and a "slave" controller. In the drawing the "master" controller comparesthe temperature of the mixture (TT1) with the setpoint. The "master" controlleroutput signal is used as the set point for the "slave" controller. This compares the"master" output signal with the temperature of the cooling water (TT2). The "slave"output adjusts the cooling water flow valve to maintain the temperature of themixture at the desired value. The advantage of this type of control is that if there is achange in the temperature of the mixture, the set point driven "slave" will begin

corrective action more quickly.

Cascade control is used mainly on slow reaction processes; in this example, largecapacity temperature control.

Figure 1-5 Cascade Control

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 12/14


1.7 FEED FORWARD CONTROL

Feed forward control is unusual on the older types of control equipment. However, itis becoming popular in µP systems, particularly in the control of largegas-turbine/centrifugal compressor units. Feed forward control is best explainedusing the following example.

Figure 1-6 Feed Forward Control

Figure 1-6 shows a liquid being heated by steam in a heat exchanger. Thecontrolled variable is the outlet temperature of the liquid (T2). T2 is maintained at aconstant temperature by controlling the flow of steam (F2). The flow control valve forthe steam is controlled by a standard controller (FC which gets its "set point" fromthe feed forward controller.

The output signal of the feed forward controller depends on both the temperature(T1) and flow rate (F1) of the liquid as it comes in. This means that any changes atthe inlet are detected "before" it affects the outlet temperatures. This means that theresponse to changes is quicker and so there is closer control of the controlled

variable.

The operator adjusts the set point on the feed forward controller so that thetemperature on the output (T2) is the same as the temperature (T2) of the set point.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 13/14


1.8 MULTI-VARIABLE CONTROL

The modern µP controller uses multi-variable control. The controller hasmathematical algorithms set into the micro-processor. These provide an outputcomputed from many different inputs . A typical example is the anti-surge controllerof a gas compressor. Figure 1-7 below shows a typical UIC system.

Figure 1-7 Multi Variable Control

The output from the UIC to the recycle valve depends on the inputs from 6 differenttransmitters. The controller normally uses a P plus I plus D control action. Thevalues of PID are set using a software programme.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y



July 1999- Rev.0

Page 14/14


1.9 ADAPTIVE CONTROL

Adaptive control is a method whereby the gain of a system can be varied dependingon the position of the set point. The following shows a simple example of why this isuseful in control systems.

Figure 1-8 Level Control of a Separator

Figure 1-8 shows the level control of a separator. The level in the separator can beset to control at position A or position B.

As the level changes the volume of liquid to be removed or added at position A ismuch greater than what must be removed or added at position B. So, for goodresponse the gain at position A should be greater than the gain at position B. The

LIC is µP based. The gain of the controller is programmed by the engineer so that itchanges when the set point is changed.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n i t N o .

1 -

B a s

i c c o n

t r o

l t h e

o r y












M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r





TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 WHAT IS GOOD CONTROL 4

2.3 TUNING A LOOP 6

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r







• Describe good loop control using simple diagrams.

• Explain how the PID settings of a controller are set to obtain good control.

• Describe modern tuning methods.

• Explain how you can get the best results by co-operating with the paneloperator.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r





2.1 INTRODUCTION

The aim of this unit is to introduce the basics of controller tuning.

2.2 WHAT IS GOOD CONTROL

Figure 2-1 Good Control

Figure 2-1 shows a typical control loop The job of the loop is to keep the measuredvariable (MV) at the set point. The loop is called a feedback control system. If flow isthe process variable, it works as follows.If the flow rate increases the error detector sends a signal to the controller. This

signal indicates how much the measured value is more than the set point (MV-SP).The controller then adjusts the correcting unit (CU) so that the MV decreases andthe flow rate goes down to the set point.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r





If the flow rate decreases to below the set-point, then the error signal is (SP-MV). Inthis case the controller adjusts the correcting unit (CU) so that the MV increases

and the flow rate goes up to the set point.

When you are tuning a loop you cannot wait for the variable to change. So, the setpoint is changed and the MV moves to the new set point. The effect on the controlloop is the same.

The graph shows the tuning of the three mode controller (PID) to give good controlfor a step set point change. The response time should be fast and the MV shouldonly go a little over the SP before it stabilises, (small overswing).

In some processes it is important to tune the system so that there is no overswing. A slow and smooth response is needed. However, some processes need a fast

response and quite big overswings are no problem. The point is you must decidewhat kind of control is good for each specific loop.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r





2.3 TUNING A LOOP

If you must tune a loop it is best to tune it when its on automatic (closed loop). It ispossible to tune it on manual (open-loop) but this can be dangerous. The operatormay not allow any open loop tuning. For any feedback control system, if the loop isclosed (the controller is on automatic), you can increase the controller gain. As youdo this, the loop will start to swing more and more. As you continue to increase thegain, you will see continuous cycling (oscillation) in the controlled variable. This isthe maximum gain at which the system may be operated before it becomesunstable. The period (time) of these continuous oscillations is called the ultimateperiod (see Figure 2-2).

Figure 2-2 Control Loop Response

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r





To determine the maximum gain and the ultimate period, take the following steps:

1 . Tune out all the reset and derivative action from the controller, leaving only

the proportional action. This means you should set T1 equal to infinity and Td equal to zero on the controller (or as close to these values as possible).

2. Maintain the controller on automatic i.e., leave the loop closed.

3. Set the gain of the proportional mode of the controller at any value. Thenmake a disturbance on the process and see what happens. One easy way ofmaking a disturbance is to move the set point for a few seconds and thenreturn it to its original value.

4. If the response curve from step 3 does not damp out, as in curve A (seeFigure 2-2), it means the gain is too high (the proportional band setting is too

low). The gain should be decreased by increasing the proportional bandsetting. Then you repeat step 3.

5. If the response curve from step 3 stops swinging, as in Curve C (see Figure2-2), it means the gain is too low (the proportional band setting is too high).The gain should be increased by decreasing the proportional band setting.Then you repeat step 3.

6. If the response from step 3 cycles continuously, as in Curve B (see Figure2-2), it means you have best possible gain (optimum proportional bandsetting). The "ultimate period" of the response curve should be noted. This isthe maximum gain at which continuous oscillations are maintained. The

ultimate period is written as PU

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r





The values obtained from step 6 are then used to set the PID of the controller. Thestandard method for setting the values of PID is the Ziegler and Nichols method asfollows:

Proportional only

Set the gain to half the maximum gain (or twice the PB setting)

Proportional plus reset.

Set the gain to 0.45 of the maximum gain (or 2.22 times the PB setting)

Set the reset to read 0.83Pu

Proportional plus reset plus derivative

Set the gain to 0.6 of the maximum gain (or 1.7 times the PB setting)

Set the rest to read 0.5 Pu.

Set the rate (derivative) to read 0.13 Pu

If you follow the above procedure it will produce a reasonably tuned loop. However,it may need to be adjusted during operation. The way the loop responds to realchanges in the process must be monitored by the operator. It can take hours for aloop to settle down to normal operational requirements. The operator must decide ifany fine tuning is required.

On older control loops the response to process changes can be seen on theink/paper recorder. A modern DCS system displays process variables on the VDU,using what are called "trend" displays. You must ask the operator to show thesedisplays when you check the loop. Normally, it is possible to print these "trend"displays as the information is stored on a hard disc (the historian). You can usuallyget a copy of what the loop has done for the last 24 hrs.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

2 -

T u n

i n g a c o n

t r o l l e r












M o d u l e

N o . 1 0 : P r o c e s s c o n t r o l f u

n d a m e n t a l

U n i t N o . 3 - I n t r o d u c t i o n t o D C S a n d P L C





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 INTRODUCTION TO DCS 4

3.2.1 The 5 Level Concept 5

3.2.2 Level Concept Description 6

3.3 PROGRAMMABLE LOGIC CONTROLLERS (PLC) 8


M o d u l e


n d a m e n t a l








• Draw a simple block diagram of a DCS system.

• Explain the 5 level DCS concept.

• Draw a simple block diagram of a PLC system.

• Explain the use of PLC in field control.

M o d u l e


n d a m e n t a l






3.1 INTRODUCTION

The aim of this unit is to introduce, in simple terms, what is meant by DCS and PLCin instrument control systems.

3.2 INTRODUCTION TO DCS

Modern control systems in the oil/gas industry now use what is called a DistributiveControl System (DCS). This means that the control of a plant (eg. refinery) is splitinto small units which are distributed around the plant.

Figure 3-1 A Simple DCS System

Figure 3-1 shows a simple DCS system. The plant consists of three separate(distributed) local control units: fractionation, compression and boiler. The loops foreach unit are controlled by a local control unit. The information required by theoperator is sent by a single cable (data highway) to the central control room. Here,the information is shown on a workstation Video Display Unit (VDU). The operatorcan adjust set points, Motor Operated Valves (MOV's) etc., from the workstationusing the same data highway. There are various manufacturers of DCS’s.Operating Companies use a variety of these systems. The following notes are givenas an introduction to the DCS system you might see.

M o d u l e


n d a m e n t a l






3.2.1 The 5 Level Concept

The layout of a particular DCS depends on the manufacturer. However, allmanufacturers make the same type of 5 level DCS as shown in Figure 3-2. Readthe diagram from the bottom (level 1) to the top (level 5).

Figure 3-2 The 5 Level DCS Concept

M o d u l e


n d a m e n t a l






3.2.2 Level Concept Description

Level 1

This is the field device level. Input devices (transmitters etc.) and output devices(control valves, etc.) are connected to input/output units (I/0 units). I/0 units convertthe 4-20mA or digital signals to specially coded signals for the fieldbus. The I/0 unitsalso convert the coded signals on the fieldbus to 4-20mA or digital signals for outputcontrol.

The fieldbus (data highway) is a cable similar to a co-axial cable (like a televisionaerial cable). It sends the coded digital signals from level 1 to the control processorsat level 2.

Level 2

This is the control level. The control processor (CP) uses the data from the fieldbusto control individual control loops. The CP can control more than one loop at a time.The PID settings are placed in the CP using a software program similar to acomputer floppy disc.

Figure 3-3 Control Processor with 5 Loops

Figure 3-3 above shows a control processor operating 5 loops (measured variables)at one time. The data on the fieldbus contains all the information for each loop inputand output. The CP, using only milliseconds of time, controls each in turn. The PIDof each is separately programmed. To the operator it looks as if all the loops arecontrolled at the same time.

M o d u l e


n d a m e n t a l






Level 3

This is the operator's supervision level. The information which is needed for eachloop is displayed on a Video Display Unit (VDU). The operator (supervisor) canadjust the set point, or he can change from manual to automatic etc. using thekeyboards on the workstation. Large control systems may have many workstationswhich display the distributed control units around the plant. Remember that loopcontrol is done from the CP. A fault on a workstation, eg. loss of picture, does notmean the plant has lost control.

Level 4

This is the local management control level. The Applications Processor (AP) takessome of the signals from the CP and puts them into a digital code (protocol) so that

they can be sent over a higher level data highway. This allows the plant engineer,plant manager, etc. to look at the plant operation remote from the Central ControlRoom (CCR), e.g. in his office. Normally, you cannot change control operationsfrom this level. It can only display information for management overview. I

Level 5

The group management level. Some signals for the AP are converted so that theycan be sent (by microwave link, satellite, etc.) to a distant headquarters. This meansthat a senior manager, at group level, can view plant operations. The workstation atheadquarters can not make changes at plant level. However, the workstationdisplays up to date information on production operations for planning purposes.

M o d u l e


n d a m e n t a l






3.3 PROGRAMMABLE LOGIC CONTROLLERS (PLC)

3.3.1 Introduction

Programmable Logic Controllers provide electronic switching operations (foremergency shut down procedures, fire and gas alarm systems, etc.). The system isnot made to control a loop or a plant. It only provides a switching sequence which iscontrolled by a software programme. Usually software programmes are written for aPLC which operates an emergency shutdown system, such as fire and gas alarms,starting electric motors and safety circuits etc. These systems can be very large.They require a systems engineer to design the software programme to operatethem. However, the following notes are given as an introduction to how thesesystems work.

Figure 3-4 Simple PLC Shutdown System

Figure 3-4 shows a simple PLC shutdown system. It has an "AND" gate with threeinput lines. These input lines consists of alarms (either high high or low low), fire

detectors (FD) and gas detectors (G D). Alarms or detectors are connected inseries to a +24V dc supply. The second "AND" gate has two inputs. One is from thefirst "AND" alarm circuit gate and the other is from the "ESD" button, which isnormally closed. The micro processor controls the shut down circuits (relays, controlvalves, solenoid valves, etc.) together with an EEPROM. The EEPROM is thememory chip which holds the shut down sequence programme. This programme isput in by the system engineer.

M o d u l e


n d a m e n t a l






Under normal working conditions all switches are closed and a "V' digital signalholds the microprocessor so that the "shutdown" devices are in their correct,

working position (energised).

If a field alarm operates or the ESD button is pressed the "AND" gate output to the

µP changes from "V to a "0". The µP now changes the output devices to their"shutdown" positions, using a logic. sequence which comes from the programme inthe EEPROM memory.

Note that all shutdown systems are made so that they are energised when they areworking normally. It is not "safe" to make the system energise for shutdown. Anequipment fault or supply problem would not shut the plant down if there was anemergency.

M o d u l e


n d a m e n t a l













M o d u l e


n d a m e n t a l

U n i t N o . 4 - H o n e r w e l l D T C 3 0 0 0 D

C S





TABLE OF CONTENTS

Para Page


4.1 INTRODUCTION 4

4.2 HONEYWELL TDC 3000 DCS 4


4.2.2 TDC 3000 System Overview 4

4.3 HONEYWELL TDC 3000 HARDWARE 7


4.3.2 The Process and Logic Manager Cabinets 7

4.3.3 UCN and LCN 10

4.3.4 Control Room Layout 11

M o d u l e


n d a m e n t a l


C S







• Explain, at block diagram level, the Honeywell TDC 3000 system.

• Explain the terms used by Honeywell for their DCS equipment.

M o d u l e


n d a m e n t a l


C S





4.1 INTRODUCTION

The aim of this unit is to introduce the Honeywell TDC 3000 and to relate the TDC3000 system to the 5 level DCS concept. The unit also explains the termsHoneywell uses for ordinary DCS equipment.

4.2 HONEYWELL TDC 3000 DCS

4.2.1 Introduction

The autodynamics simulator which you used when you learned about controlsystems uses the graphics (pictures and symbols) of the Honeywell TDC 3000

workstation. The displays of PFD's, trends, indicators, alarms etc. are the same asyou will see on a real control room VDU. This unit is given to show the layout of theTDC 3000 system which provides the signals seen on the VDU.

4.2.2 TDC 3000 System Overview

Figure 4-1 is a simplified diagram of the components of the Honeywell TDC (totallydistributed control) 3000 DCS. The notes at the side show how the TDC 3000 fits ageneralised DCS system. The Honeywell TDC 3000 is a newer version of the olderTDC 2000. Therefore, it has extra items not seen on the older systems. The mainfeatures are as follows:

1. Loop control (4-20mA, smart or digital) is carried out by the processmanager (PM). The I/0 units for the loops can be placed locally (inside thesame cabinet as the PM) or placed at a remote location in the plant. Remotesignals are sent using a serial data transmission link (RS422 standard) tothe PM.

2. The switched signals (e.g. alarms, valve positions, fire detectors, gasdetectors, etc.) are processed separately using a Logic Manager (LM). TheI/0 units for the Logic Manager can be either local or remote in the sameway as the PM.

3. The PM uses a microprocessor to control the loops. This µP can be

programmed to set the PID for each loop as required. The µP may also beable to tune the loops automatically for best response. It has an auto-tunefacility.

4. The LM uses a microprocessor to operate the PLC. The Logic Manager µPis programmed by the systems engineer to give the correct shutdownsequences etc.

M o d u l e


n d a m e n t a l


C S





5. Signals needed by -the supervisors on the workstations are transmitted via aUniversal Control Network (UCN). This network is not compatible with the

workstation local area network, (called a Local Control Network (LCN) byHoneywell). Therefore, a Network Interface Module (NIM) is used.

6. The LCN data highway provides the signals to...

• The operators workstations (VDU and keyboards). These are calledUniversal Stations (US) by Honeywell.

• Printers

• Historian (History Module). This contains a redundant hard discsystem which stores operating information so that "trends" can be

printed or displayed.

• Gateways

• These gateways process signals which can be sent to amanagement workstation. The diagram shows a gateway whichchanges LCN data so that it can be sent on an "ETHERNET" highlevel data LAN. A gateway can be provided to operate a modem. Themodem can send signals by radio to the headquarters managementif required.

• Because Honeywell uses its own system for data management (theUCN), other systems have to be connected by special DataConversion units. These are called Minicop Modules (MM). Typicalsystems that may be connected to the TDC 3000 are crude meteringsystems, tank gauging systems, compressor control systems etc.

• To make the system more reliable many of the units run on what iscalled a "Redundant" system. This means that there are two units foreach operation (e.g. UCN links, NIM, Historian, etc.). If one doesn'twork the other takes over automatically.

M o d u l e


n d a m e n t a l


C S





Figure 4-1 Simplified Block Diagram Honeywell TDC 3000

M o d u l e


n d a m e n t a l


C S





4.3 HONEYWELL TDC 3000 HARDWARE

4.3.1 Introduction

The following diagrams are given, with a brief description, to show what theHoneywell TDC 3000 hardware looks like._

4.3.2 The Process and Logic Manager Cabinets

Both cabinets are the same size (shown on the LM in Figure 4-2) and are normallyplaced side by side in the instrument equipment room. The number of each cabinetdepends on the installation.

LOGIC MANAGER CABINET

Figure 4-2 shows the layout of a typical logic manager. The top two racks containthe cards required to make the logic manager and the redundant partner. Thebottom two racks contain the 1/0 cards for parallel and serial operation.

Parallel operation I/0 cards are used for loops near the LM rack (less than 30m).Serial operation I/0 cards are used for processing serial data coming from remotelocations (RS 422 link).

The cards which are fitted into the slots of each cabinet can be removed easily.They are connected to the system by printed board edge connectors. Normallythese cards can not be repaired. The whole card is replaced if it does not work. Thebroken card is sent back to Honeywell for repair.

The LM supplies power at 110V DC and 240V DC. This provides the switchingvoltages for both input devices (e.g. alarm switches) and output devices (e.g.solenoid valves).

PROCESS MANAGER CABINET.

Figure 4-3 shows the layout of a typical process manager. The top rack contains the

input/output cards (called IOP cards by Honeywell). Racks 2 and 3 contain theredundant process manager cards. The bottom of the cabinet contains the powersupplies to operate both the process manager and IOP cards. It also provides the24V DC needed to drive the loops etc.

Note: All loops are connected to the back of the racks through the safety barriers.The Honeywell system is not intrinsically safe.

M o d u l e


n d a m e n t a l


C S





LOGIC MANAGER CABINET -

Figure 4-2 Logic Manager

M o d u l e


n d a m e n t a l


C S





PROCESS MANAGER CABINET

Figure 4-3 Process Manager Cabinet

M o d u l e


n d a m e n t a l


C S





4.3.3 UCN and LCN

The UCN and LCN are both redundant co-axial cables. The nodes (taps) on thesecables are specially made so that if they are disconnected the lines are not broken.The other connected units continue working. Each cable has a special terminator

(75Ω. This must not be removed as it stops signals which reach the end of thecable from being reflected. Any reflected signals will interfere with processing dataand produce errors.

Figure 4-4 shows a redundant UCN as an example.

Figure 4-4 The UCN Network

M o d u l e


n d a m e n t a l


C S





4.3.4 Control Room Layout

The universal stations provide the human interface with the TDC 3000 systems. Themake up of each individual control room depends on the user's needs. It is made upof what Honeywell call "Optimum Replaceable Units" (ORU). A typical arrangementof a control room is shown in Figure 4-5.

Figure 4-5 Supervisors Control Centre

M o d u l e


n d a m e n t a l


C S





The following points should be noted on the typical Honeywell TDC 3000supervisors control room.

1. Cartridge/Floppy disc drives similar to a PC drive are optional extras. Theseallow new operating programmes to be added.

2. The matrix printer is used to print plant operations history for managementoverview.

3. Some instrument/process engineers find the old type of pen recorders aconvenient way of showing trends. These can be added to the system ifrequired.

4. The engineer can connect a portable keyboard into the system. This

keyboard is used to re-configure the system as required.

5. The latest Honeywell US has a touch screen facility . To change the displaythe keyboard is not required. Touch the screen and the display changes asthe operator instructs.

6. The Trackball is the same as an ordinary PC mouse. Rotate the ball and thecursor moves, to the required position on the screen. A trackball is only amouse upside down.

7. The electronics modules are contained in what Honeywell call a 5 slotchassis. These 5 slot chassis contain the electronics to drive the US,

Historian, Gateways, etc.

8. The Network Interface Module (NIM), which is fully redundant, is usuallyhoused as shown.

M o d u l e


n d a m e n t a l


C S



July 1999- Rev.0

Page 1/12









M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 2/12


TABLE OF CONTENTS

Para Page


5.1 INTRODUCTION 4

5.2 THE BASIC FOXBORO IA SYSTEM 4


5.2.2 Foxboro IA System Layout. 4

5.2.3 Foxboro IA Hardware 7

5.3 TYPICAL FOXBORO IA CENTRAL CONTROL ROOM 10

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 3/12




• Explain the terms used by Foxboro in their DCS.

• Sketch the layout of the Foxboro enclosure.

• Draw a simplified diagram of the Foxboro DCS and explain what the maincomponents do.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 4/12


5.1 INTRODUCTION

The aim of the unit is to introduce the Foxboro Intelligent Automation (Fox IA) DCS.It explains the terms used by Foxboro and shows how IA fits the 5 level concept of adistributed control system.

5.2 THE BASIC FOXBORO IA SYSTEM

5.2.1 Introduction

5.2.2 Foxboro IA System Layout.

The Foxboro IA system is one of the most up to date distributed control systems foroil/gas production. The Foxboro system is an improvement on older DCS's as ituses an "Open Industrial System". This means the software used to programme theDCS is industrial standard (UNIX). It can be used to set up both the Foxboro systemand equipment from other manufacturers connected to it.

It has improved data handling so there is no need for "handshaking". It is also has asystem called "Reporting by Exception". This means that measurements are onlychanged if their values change.

I Figure 5-1 shows the layout of a typical Foxboro IA DCS. The levels of control arethe same as the Honeywell but the system is simpler at the 1, 2 and 3 level. So, itonly needs one data transmission highway. The following points should be noted.

1) The diagram shows a large Integrated Control System (e.g. control andmanagement of a multi-platform offshore oil field). The supervision level islocated on each platform. The area management level consists of a centralcontrol room. This is usually on the accommodation platform. It can displayinformation from all the platforms. The group management display is at theheadquarters on shore. Data transmission between units can be either bycable using a high level LAN (ETHERNET) or by radio link (e.g. satellite,microwave link, etc.)

2) The 1/0 conditioning units and the control processors are located in one unit.This can be placed anywhere in the plant.

3) Signals to and from the control room are placed on what Foxboro call a"Redundant Nodebus". The same cable is used for the control room andfield units. If the field units are a long way from the control room a "NodebusExtender" (NBE) is used. This maintains the voltage level of the transmitteddata.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 5/12


4) The following processors are connected to the nodebus:

AP - Applications Processor. This allows data to beprocessed for the Historian, Printer, etc.

WP - Workstation Processor. This allows data to beprocessed for the workstation, (e.g. VDU, keyboard,mouse/trackball, touch screen, etc.).

Comm - Communications Processor. This allows data to beprocessed for items not using UNIX, (mainly theengineer's PC which uses ASCII)

FDG - Foreign Device Gateway Processor. This allows data

to be processed so that signals can be received orsent through a modem. The data can be sent toanother location, platform, etc.

CBLI - Carrier Based LAN Interface. This unit converts theUNIX programming system (protocol) of the nodebusto a protocol for the high level LAN (e.g. Ethernet) andvice-versa. The area management system uses thesame equipment as in the control room. Therefore,there must be a CBLI at both ends of the high levelLAN.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 6/12


Figure 5-1 Foxboro IA DCS Overview

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 7/12


5.2.3 Foxboro IA Hardware

Foxboro combines the first level (field devices) and second level (control devices)into one unit. This unit is called an "Enclosure". It can be placed at any suitableposition in the plant. Figure 5-2 shows a Foxboro enclosure in a plant.

Figure 5-2 Foxboro IA Enclosure

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 8/12


Figure 5-3 Foxboro Industrial Enclosure

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 9/12


Figure 5-3 shows the inside of an enclosure. The bottom two racks have slots intowhich the 1/0 units are fitted. These are called Field Bus Modules (FBM) by

Foxboro. These FBM's can process any type of field input/output.

Some FBM examples are given below.

The top of the enclosure has slots which hold the system processors (calledstations by Foxboro). A plant enclosure normally has only CP's and NBE's. TheCP's control the area loops and the NBE extends the redundant nodebus to thesupervisor's control room.

FBM FUNCTION POINTSFBM 01 0-20 mA INPUT 8 AI

FBM 02 THERMOCOUPLE 1mV INPUT 8 A]

FBM 03 RTD INPUT 8 AI

FBM 04 0-20mA INPUT 1 OUTPUT .4A1/4A0

FBM 10 120 VDC INPUT / OUTPUT SWITCHED 8D1/8DO

FBM 18 SMART TRANSMITTERS 8DA1

AI ANALOG INPUT

DI DIGITAL INPUT

AO ANALOG OUTPUT

DO DIGITAL OUTPUT

POINTS Number of inputs/outputs available on each FBM

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 10/12


5.3 TYPICAL FOXBORO IA CENTRAL CONTROL ROOM

Figure 5-4 Foxboro IA CCR

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 11/12


Figure 5-4 shows the typical layout of a Foxboro Central Control Room (CCR).

A basic description of the system is as follows:

1) The Central Control Room processes signals from both a remote location,using a CBLI, and from equipment on the main platform where the CCR islocated.

2) Main platform signals are routed through what are called marshallingcabinets. These contain the IS barriers. A Foxboro [A FBM is not intrinsicallysafe.

3) The industrial enclosures are the same as the ones described in 5.3.2.However, they need no weather-proofing and Zone 1 protection. These areusually located in a terminal room behind the CCR.

4) Whether the system is for local supervisory control or CCR control theequipment is the same. It is all run from a Redundant Nodebus connectedby either NBEs or CBLIs.

5) The AP, WP, and COMM processors can be fitted into a station in theenclosure or in slots under the workstations.

6) The Nodebus Interface (NBI) connects the Nodebus to the engineers PC.This is done so that the engineer does not interfere with operators using theworkstations.

7) The Nodebus has terminators to stop data reflections, (in the same way asthe Honeywell TDC 3000).

8) All Nodebus connectors can be removed without affecting the other unitsconnected to the bus.

9) Remember that loop control is done by the CP. A fault on the CCR Nodebuswill not cause the plant to lose control.

10) The operator on the workstation normally only supervises the plantoperations. However, he can switch a control loop from automatic to manual

and perform set point changes.

11) PID control functions and PLC sequence changes can only be done by thesystems technician or engineer. This is usually done via the engineer's PCusing a "password" know only to the engineering staff.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S



July 1999- Rev.0

Page 12/12


12) Figure 5-5 shows the typical layout of a Foxboro control room.

Figure 5-5 Foxboro IA Workstations

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

5 -

F o x

b o r o

I A D C S







UNIT 2 TUNING A CONTROLLER.





M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





TABLE OF CONTENTS

Para Page

PRACTICAL TASK 1 3

PRACTICAL TASK 2 8

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





PRACTICAL TASK 1

Introduction

CASCADE CONTROL

The Autodynamics simulator will be used to demonstrate cascade control. Theprocess variable to be controlled is the level in a tank. A liquid storage tank is usedto store a liquid before it is sent for downstream processing. The liquid has avariable density. Figure PT 1 shows the PFD and P and ID of the process.

The normal operating conditions for the loop are:

HCV-431 is open 50% to give a flow rate of 100 TPH entering V-400. The cascadeloop maintains the level at 50% (half way) for a flow rate of 100 TPH.

Alarm settings

FAH/L 402 Above 160 TPH or below 60 TPH.

LAH/L 461 Above 75% or below 25%.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





Figure PT - 1a Process Flow Diagram (PFD).Level Control.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





Figure PT 1b P & ID Level Control

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





PRACTICAL PROCEDURE

PART 1

1) Make sure the Autodynamics simulator is operating as designed. Module 4Level Control.

The VDU screen shows:

FI-401 READS 100 TPH

FIRC-402 READS 100 TPH

HV-432 OPEN

HCV-431 READS 50%

LIRC-431 READS 50%

PI-412 READS 0.6 kg/cm2g

1

2) a) What happens if you adjust the set point of FIRC-402.

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

b) Explain the result of part 2 (a)

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





PART 2

1 Place FIRC-402 to manual.

2. Open HCV-431 so that it reads 60%

3. Using the manual output control of FIRC-402, try and maintain the level ofV-400 at 50%.

4. Estimate the time taken to bring the level under control.

PART 3

1. Return the simulator to normal designed condition, with full automaticcontrol.

2. Increase HCV-431 so that it is 60% open.

3. Estimate the time taken to bring the level under control.

4. Does cascade control produce faster response in the system?

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





PRACTICAL TASK 2

Introduction

RATIO CONTROL

This task uses the Autodynamic simulator to show the operation of ratio control.Ratio control is used to produce a mixed product for tanker loading. It is possiblewith the simulation to switch from ratio to cascade operation, using a productanalyser. This is also demonstrated.

Figure PT 2 gives the VDU display (PFD) and the P & ID for the process.

Mixing Operation

The mixing operation is used in the in-line blender to mix the available components.The components are blended to meet product demands and product specification.The mixing components for this operation are a heavy product feed and a lightproduct feed.

The blended product for loading meets quality specifications using a ratio orcascade control system. Under normal operation the ratio control is used for startup and cascade control for normal running. Ratio control sets the required mixtureof heavy and light products. The cascade control is run by an analyser. It makessure the correct ratio is maintained after the initial settings are made by the ratiocontrol.

Logic Control

This simulation has a PLC system added to provide the following safety function.Block valves HV-526 and HV-528 automatically close when the total volume of therespective trucks reaches 20 m

3 (2000 litres). All flows stop, and the high volume

alarm comes on. To restart the loading of another tanker the system must be resetby switches HS-531 or HS-532. These switches must be switched "Off" again afterresetting. The PLC logic will not allow the block valve (HV-526 or HV-528) to open ifthe reset is left "On".

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





Figure PT-2(a) Product Mixing FPD

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





Figure PT-2(b) Product Mixing P & ID

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





PRACTICAL PROCEDURE

Introduction

To show how ratio control is done, the simulator exercise 5020 Module 5 will becarried out from the closed down position. The object will be to load a tanker with20m3 (2000 litres) of SG 0.7 product.

Note:

The ratio calculation is done as follows (this is done automatically by theloading system).

Let X = Quantity of Heavy product.

Let Y = Quantity of Light product.

Then (0.8 x X) + (0.4 x Y) = (X + Y)0.7

0.8X + 0.4 Y = 0.7X + 0.7Y

0.8X - 0.7X = 0.7Y - 0.4Y

0.1X = 0.3Y

The ratio of heavy to light product is 3:1

1. The storage tank (slops tank) holds poor quality produce that cannot besold. HV-526 must not be opened until AIRC-502 reads the correct qualityon automatic. When the tanker is fully loaded the system will stopautomatically. Make sure you don't open HV-525 until the AIRC-502 is onautomatic.

2. Remember to reset the totalizer after the tanker is loaded. Otherwise thePLC logic will not allow another tanker to be loaded.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s





PART 1

START UP

1) OPEN the storage tank block valve (HV-527).

2) Turn ON HS-51 5 to start the heavy product feed pump (P-f51 5).

3) With FIC-501 on manual, increase the output of FIC-501 to 10%.This will open the heavy feed valve (FCV-501).

4) With FIC-503 on manual opens the light product feed valve by increasing theoutput of FIC-503 to 10%.

5) Adjust the setpoint of FIC-501 to equal its process variable and transfer the

controller to AUTOMATIC.

6) Check the value at AIRC-502 for the specific gravity of the mixed liquid. Ifthe specific gravity is undesirable, adjust the light f low through FCV-503.

7) Adjust the ratio of heavy feed to light feed by adjusting the value at HC-20.

8) Switch HS-529 to RATIO CONTROL, and place FIC-503 in the CASCADE mode.

9) Continue to gradually increase the setpoint of FIC-501 to design(113.6m

3/hr). The ratio controller HC-20 will automatically adjust the light

flow through FCV-503. The specific gravity will not change.

10) Perform a bumpless transfer to place AIRC-502 in control in the followingmanner:

a) Divide the measured variable of FIC-501 by the instrument range.

b) Multiply that number by the ratio factor set on HC-20.

c) Convert that number to output percent by multiplying by a factor of100.

d) This number becomes the required output setting for AIRC 502.

e) Adjust the output of AIRC-502 to the number above.

f) Switch HS-529 to the FEEDBACK condition.

g) Switch AIRC-502 to AUTOMATIC.

11) Begin loading tanker no. 1 by putting HV-526 in the OP condition andswitching the storage tank block valve (HV-527 CLOSED.

M o

d u

l e

N o .

1 0 :

P r o c e s s c o n

t r o

l f u

n d a m e n

t a l

U n

i t N o .

6 -

P r a c

t i c a

l t a

s k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 11

INSTRUMENT CRAFT PRACTICE



July 1999- Rev.0

Page 1/13



UNIT 1 WORKSHOP SAFETY AND TOOL CARE

UNIT 2 BASIC HAND TOOLS

UNIT 3 TUBING SYSTEMS

UNIT 4 CRIMPING


M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 2/13


TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION 4

1.2 WORKSHOP RULES 4

1.3 PERSONAL PROTECTION 6

1.3.1 Body Protection 6

1.3.2 Head Protection 7

1.3.3 Eye Protection 8

1.3.4 Hand Protection 9

1.3.5 Foot Protection 10

1.4 CARE OF TOOLS 11

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 3/13



The trainee will be able to:

• List the general safety rules used in the workshop.

• Identify the items of personal protection commonly used in the workshop.

• List the general rules for tool care.

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 4/13


1.1 INTRODUCTION

To become a skilled craftsman, a trainee must learn to work safely.

He must think of his own safety and the safety of other workers. The safest way ofdoing the job is the best way. Accidents are caused by careless work habits. Theydo not just happen, they, are caused. There is always the possibility of accidentswhen people are working with tools and equipment. These accidents can be costlyand painful. Everyone must try to prevent accidents. Managers try to preventaccidents by providing:

1. Workshop rules

2. Protective clothing and personal safety equipment

3. Safe tools and equipment

These items alone cannot prevent accidents unless the workers do their part tohelp. The responsibility of the worker is to:

1 . Follow the workshop rules.

2. Use protective clothing and equipment.

3. Use tools and equipment correctly.

1.2 WORKSHOP RULES

Every workshop has its own safety rules. These rules will vary according to thedifferent equipment in each workshop. It is every trainee's responsibility to learnthese rules and then follow them. The purpose of workshop rules is to protect youand your fellow workers. The rules will not protect workers who do not learn andfollow them. Although the rules vary from workshop to workshop there are somerules that apply to all workshops.

1. Know your job:

You, should know what you are going to do, how-to do it, and the toolsneeded before you begin work.

2. Good housekeeping:

Keep your work area neat and tidy. Unused parts, scrap material or tools,left lying around your work area will cause accidents.

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 5/13


3. Conduct:

A sudden interruption to a worker who is busy doing his job is dangerous; hecould hurt himself or another worker.

4. Clothing

The type of clothing needed depends on the job and its dangers. Working inhot areas may require light, loose fitting clothes. Working near rotatingequipment means not wearing loose clothes that can be caught. Some other jobs require special protection, such as hard hats, goggles, or safety shoes.

5. Think safety:

Being a skilled worker and knowing all the safety rules does not mean youwill be a safe worker. You must think about safety at all times.

6. Being alert:

Although you may be a safe worker yourself, beware of others around you.They may endanger you if they are using machine tools, grinding, orwelding.

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 6/13


1.3 PERSONAL PROTECTION

Wearing personal protection is important for developing good work habits. As wellas protecting the body, you must protect your head, eyes, hands and feet.

Some suitable equipment for personal protection is as follows:

1.3.1 Body Protection

For general workshop work a coverall is the safest and most practical form of bodyprotection. Figure 1-1 below shows the safe way to dress in the workshop.

Figure 1-1 The Workshop Dress

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 7/13


For extra protection, workers are sometimes required to wear canvas aprons. Theyare worn in machine shops when using drilling or grinding equipment (see Figure

1-2).

Figure 1-2 The Canvas Apron

1.3.2 Head Protection

In some work areas it is necessary to wear hard hats. These areas are usuallyplaces where work is going on above head height. Long hair is also a problem in theworkshop where -there is rotating equipment. If the hair is caught it can causeserious injury.

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 8/13


1.3.3 Eye Protection

Eye protection should be worn in any work situation where there are flying objects.Jobs such as grinding, cutting, or machining require eye protection. Welding andfurnace operations require tinted safety glasses or goggles to protect the eyes fromtoo much light or flying objects. Safety glasses are similar to regular glasses exceptthat the lenses are strong. Safety glasses only protect your eyes from the front. Youcan put side shields on the glasses to help protect the eyes from the side. Typicalsafety glasses are shown in Figure 1-3.

Figure 1-3 Safety Glasses

Safety goggles are designed to provide more eye protection because they fit theface better. Goggles are kept in place with a head strap so they do not fall off aseasily as safety glasses. The safety lenses are made of clear hard plastic. Thelenses allow you to see but prevent flying objects from hitting your eyes. The choiceof wearing safety glasses or goggles depends on the task being performed (seeFigure 1-4).

Figure 1-4 Safety Goggles

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 9/13


Face shields give full face protection and are good for people who wear ordinaryglasses. They allow air to circulate between the face and shield so the glasses do

not mist up. When you are working in areas where there are hot flying particles,face masks must be worn (see Figure 1-5).

Figure 1-5 The Face Mask

1.3.4 Hand Protection

Gloves should be worn when handling sharp objects, such as sheet metal, casings,machined components and swarf. Gloves must be the correct type for the job, andthey must be in good condition. However, gloves should never be worn whenoperating moving machinery. Most gloves are made of either leather, heavy cloth,canvas, rubber, or plastic. They are designed to prevent cuts from sharp edges, orburns from hot metal. Plastic gloves are worn when handling chemicals.

Figure 1-6 Safety Gloves

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 10/13


1.3.5 Foot Protection

Safety footwear are designed to protect the feet. They must be worn at all times

around the plant and in the workshop area. They are reinforced with steel at thetoes to prevent the toes from being crushed by falling objects. If you drop a heavyobject on your toes it can cause a serious injury and can be very painful. The solesare non-slip and are often reinforced to prevent puncture by sharp objects.

Figure 1-7 Safety Shoes

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 11/13


1.4 CARE OF TOOLS

It is important to make sure that tools are kept in good condition. Worn or damaged

tools can cause injuries. A few examples of poorly maintained tools are shown inFigure 1-8.

Figure 1-8 Poorly Maintained Tool

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 12/13


The following is a list of general guide lines for the care of tools and equipment.

Store tools in the proper place

Each tool should have its own special place to be stored when it is not being used.When the job is finished, return the tool to its proper storage place. Putting themaway immediately helps prevent them from being lost. Tools lying around theworkshop can cause accidents; eg, tripping over an electric drill left on the ground.

Care of delicate tools

Some tools require special storage because they can be easily damaged.Measuring tools and instrument screwdrivers are good examples. They are soondamaged if they are thrown down or dropped. Take a little time to ensure that thesetools are in a safe place when they are not being used.

Regular inspection of tools and equipment

Even with the best care, tools can become damaged and equipment worn. Someequipment has inspection and maintenance procedures provided by themanufacturer. These inspection procedures should be followed carefully.

Small hand tools should be checked regularly. They should be repaired or replacedif they are defective. Electrically powered tools can be particularly dangerous if thecable is damaged; they become a fire hazard.

Correct use of hand tools and equipment

Using a tool for a job that it was designed for will not damage it. Some tool parts,like hacksaw blades, are replaceable, but the tool itself should not get damaged. Ifyou use tools for other purposes they can be permanently damaged; eg, usingwrenches as hammers and screwdrivers as levers.

Tools are designed to be held and used in a certain way. Using tools wrongly willmake the tool less effective and will cause damage. As an example, some powertools have guards or safety devices. It is very dangerous to remove the guards.

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 13/13


Using the correct size tool

Many tools come in different sizes. The size of the tool must suit the job it is to do.

Using the wrong size tool is almost as dangerous as using the wrong tool. Using asmall screwdriver to turn a large screw, or the wrong sized wrench to turn a nut isdangerous.

Keep tools and equipment clean

Very little time is needed to clean your tools when you have finished the job. No

one likes dirty tools or equipment. Keeping your tools clean shows you have pride inyour work. Dirt and grease can destroy many tools.

M o

d u l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p r a c

t i c e

U n

i t N o .

1 -

W o

r k s

h o p s a

f e t y a n

d t o o

l s c a r e



July 1999- Rev.0

Page 1/20






UNIT 4 CRIMPING


M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 2/20


TABLE OF CONTENTS

Para Page


2.1 INTRODUCTION 4

2.2 VICE AND CLAMPS 4

2.3 MEASURING INSTRUMENTS 7

2.4 HAMMERS 9

2.5 PUNCHES 10

2.6 FILES 11

2.7 PLIERS 12

2.8 WRENCHES 13

2.9 DRILLS, TAPS AND DIES 17

2.10 THE POWER DRILL 19

2.11 PNEUMATIC IMPACT WRENCH 20

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 3/20



The student will be able to explain the use of the following hand tools.

• Vices and clamps

• Rules, set squares and protractors

• Hammers

• Punches

• Files

• Pliers

• Wrenches

• Drills, tapes and dies

• Power drill

• Pneumatic impact wrench

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 4/20


2.1 INTRODUCTION

The aim of this unit is to describe and give the uses of the basic hand tools used bythe instrument technician.

2.2 VICE AND CLAMPS

The Engineer's Bench Vice

Bench vices are bolted to the top of the workbench. They are used to hold theworkpiece in the right place. The vice should be between 38 to 46 inches from theground, depending on the workman's elbow height (see Figure 2-1).

Figure 2-1 Typical Bench Vice

Often bench vices have a base which can be turned so that the work can bepositioned at a required angle. The vice is locked in place with a lock nut. The

material is held between the jaws by tightening the screw handle. The jaws areusually serrated to grip the work. Soft jaws should be used to protect work whichcan be scratched easily. Soft jaws are made from a soft material such as rubber oraluminium. They are fitted over the normal vice jaws.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 5/20


Another type of hand vice is the machine vice. This is bolted onto the base of thedrilling machine to hold small items for drilling (see Figure 2-2).

Figure 2-2 Machine Vice

Pipe Bench Vice

The pipe vice is another common bench vice which must be bolted to a workbench(see Figure 2-3).

Figure 2-3 Typical Pipe Vice

Pipe can be inserted into the vice by undoing the hook on the side, which allows theframe to open. The pipe is placed on the bottom jaw, then the hook is brought backover and locked in place. The hand wheel is used to make the final tightness of thepipe in the vice. Pipe vices are made in various sizes and styles. The size of the

vice depends on the size of the pipe it is to hold. The vice should be large enough tohold the pipe but not large enough to crush it. The pipe vice is used instead of thebench vice for clamping round work. The V-shaped jaws allow more contact with thework. This gives a better grip. M

o d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 6/20


C Clamp

C Clamps do the same job as a vice. They are used to hold the workpiece securewhile you are working on it. They are portable but they clamp work to the bench.They are usually used on rough material where scratches are not a problem. CClamps have four main parts: the frame, the screw, the handle, and the swivel pad(see Figure 2-4).

Toolmakers Clamps

Toolmakers clamps (parallel clamps) are used on surfaces which must not bedamaged. They come in a range of sizes, which depends on the size of the materialto be held (see Figure 2-5).

Figure 2-5 Typical Toolmaker's Clamp

Figure 2-4 Typical C Clamps

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 7/20




July 1999- Rev.0

Page 8/20


2.3 MEASURING INSTRUMENTS

These are the instruments used for marking out a job. Normally the instrumenttechnician will use only three. The steel rule, set square and protractor.

The Steel Rule

The engineer's precision steel rule is one of the most frequently used measuringtools in the workshop. They are marked with either imperial or metric graduations,or both. They are made from hardened and tempered spring steel.

A metric rule usually comes in lengths of 15cm and 30cm. The measuring accuracyof a rule is up to ± 0.2mm. On a metric rule the longest graduation lines are forcentimetres. The centimetre lines are divided into ten smaller graduations for

millimetres. Some rules have smaller 1/2mm graduations between the mmgraduations (see Figure 2-6) below.

Figure 2-6 The Steel Rule 1

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 9/20


The Set Square

A precision engineer's square is used to ensure the work material is square, and todraw straight lines at 90° to the datum faces. The lines drawn will be parallel to the

other datum edge. Squares have a steel blade and handle, which are at 90° to eachother. Some squares have measuring graduations on the blades (see Figure 2-7)

Figure 2-7 The Set Square

The Protractor

The protractor is used to find or measure angles from 0° to 180°. The flat edge ofthe protractor head is placed on one side of the angle being measured. Then theedge of the rule is placed on the other side of the angle. The angle can be readstraight off the dial on the protractor head.

Figure 2-8 The Protractor

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 10/20


2.4 HAMMERS

The most common type of hammer is the ball-pein hammer. The main parts of theball-pein hammer are: the face (the flat striking surface), the pein (the round face),the wedge (used to hold the hammer head to the shaft), the eye (the hole into whichthe shaft is fitted), and the shaft or handle. The flat face is for hammering, and thepein is for rounding off rivets etc.

Soft-faced hammers, or mallets, are used instead of steel hammers when workingon machined surfaces or fragile parts. They are used especially for assembling ordismantling parts so that the finished surfaces are not harmed. These hammers arecommonly made of plastic, copper, or rubber. Typical examples of these hammersare shown in Figure 2-9.

Figure 2-9 Typical Workshop Hammers

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 11/20


2.5 PUNCHES

Centre Punch

Before any hole is drilled, you must make an indentation with a centre punch, wherethe hole is to be drilled (this is to stop the drill from slipping). The centre punch is aprecision tool so you must be careful to place the point of the punch exactly at thecentre of the hole location (see Figure 2-10).

Pin Punches

Figure 2-10 The Centre Punch

These are specially made tools for the removal of pins etc. A typical example of thistype of punch is shown in Figure 2-11. They are usually in sets of about 15 rangingfrom 1 mm to 10mm.

Figure 2-11 The Pin Punch

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 12/20


2.6 FILES

A file is a hand-held cutting tool which is made from good quality tool steel. The

blade is hardened, but the tang is soft to take a wooden handle. Files come in allshapes and sizes, e.g. flat, square, round, triangular etc. They are used by theinstrument technician for cleaning burrs from tubing, holes etc.

A good instrument tool kit will also contain a set of miniature files for use in contactcleaning. A few examples of files found in the workshop are shown in Figure 2-12.

VERY HIGH QUALITY INDUSTRIAL STANDARD NEEDLE FILES COATED WITHDIAMOND GRIT ENABLING THEM TO FILE MATERIALS SUCH AS TUNGSTENCARBIDE, CERAMICS, CARBON, GLASS, HARDENED STEELS ETC. THE SETCOMPRISES SIX POPULAR PROFILES: HAND, ROUND , HALFROUND ,SQUARE, THREE SQUARE AND TAPERFLAT.

Figure 2-12 Typical Workshop Files

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 13/20




July 1999- Rev.0

Page 14/20


2.7 PLIERS

Pliers are used for gripping and holding small parts during assembly work. They are

also used for bending cables and wires to be connected to instruments. Many typesof instrument pliers also have a cutting edge for cutting cables to the correct length.Pliers come in all shapes and sizes. Figure 2-13 shows some common workshoppliers.

Figure 2-13 Common Pliers

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 15/20


2.8 WRENCHES

Wrenches are used to tighten or remove nuts and bolts. They come in many

different forms. The following are the ones most commonly found in an instrumentworkshop.

Spanner Wrenches

Spanner wrenches are used for fastening and removing nuts and bolts. There arethree common types of spanner wrench. They are open ended, ring and adjustable.Figure 2-14 shows examples of these types.

Figure 2-14 Typical Spanners

Note: Don't use an adjustable spanner if the correct size spanner is available.The repeated use of an adjustable spanner will destroy the flat sides onthe nut or bolt.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 16/20


Socket Wrench Set

Socket wrench sets are made in a wide range of sizes, but all of them have square

drives. They are made in both standard and extended length. Extended lengthsockets are used in restricted places. A set of socket wrenches will include a rangeof attachments, such as: a reversible ratchet, sliding tee, extension bars, universal joints etc. They are very useful tools because they place the load at 12 pointsaround the nut, and they can be used in places where a spanner can't be used. Atypical socket set is shown in Figure 2-15.

A ADAPTER K REGULAR 6 POINT SOCKET

B,C,E EXTENSION BARS L REGULAR 12 POINT SOCKET

D SLIDING T HANDLE M HEX SOCKET SCREW SOCKET

F DEEP 6 POINT SOCKET N UNIVERSAL 12 POINT SOCKET

G DEEP 12 POINT SOCKET 0 FLEX HANDLE

H SPARK PLUG SOCKET P FLEX HEAD RATCHET

I SPEEDER HANDLE Q REVERSIBLE RATCHET

J RATCHET ADAPTER R UNIVERSAL JOINT

Figure 2-15 Socket Wrench Set

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 17/20


Torque Wrenches.

Torque wrenches are wrenches which are used to tighten bolts to a set tightness.

They can be either of the open ended type or have a square drive which fits into a6/12 point socket similar to a socket wrench set. The wrench has a built in indicatorwhich shows the torque applied in either Ibf-in or N-m. The wrench will start to slipwhen the set torque is reached so that no more torque can be applied. Remember,torque is the force applied times the perpendicular distance as shown.

A typical torque wrench is shown in Figure 2-16.

Figure 2-16 Torque Wrench

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 18/20


Allen Wrenches

An Allen wrench is an "L" shaped piece of hexagonal tool steel. They are designed

for fastening or loosening Allen set screws. A set of Allen wrenches come in arange of metric and imperial sizes. The size is taken across the flats of the-wrench(see Figure 2-17)

Figure 2-17 Allen Wrenches

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 19/20


2.9 DRILLS, TAPS AND DIES

Twist Drill

Twist drills are the cutting tools used to produce holes in most types of material.The drill bits are made from high-speed steel. Standard bits have two helicalgrooves, or flutes, cut lengthways around the body of the drill. They provide cuttingedges, admit cutting fluid, and allow space for the cuttings to escape during drilling.The bit is made so that it can be held by a chuck fitted on the drilling machine. Thedrilling machine provides the power for making the holes. Figure 2-18 shows atypical twist drill bit.

Figure 2-18 Typical Twist Drill

TAPS

Taps are cutting tools used to cut internal threads. They are mad from high-quality

tool steel, hardened and ground.

Figure 2-19 Taps

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 20/20


Figure 2-19 shows the main parts of a tap. The shank is the body of the tap. Thelands are the cutting edges. The chamfer is the angle at the leading end of the tap.The tap is chamfered to make it easier to start in a drilled hole (taper tap). The

flutes are the grooves between the lands. The flutes allow the metal cuttings to fallaway from the -lands. The square on the end of the shank is used to attach a tapwrench. Threading a hole with a tap is done by hand, using a tap wrench (seeFigure 2-20). When tapping a hole make sure the tap is at right angles(perpendicular) to the hole, otherwise you will make uneven and cracked threads.

Figure 2-20 Tapping with a Tap Wrench

Dies

The "die" is used to make an external thread on a bar to make a screw. The die isheld in a device similar to a tap wrench and the thread is produced by turning thedie around the bar being threaded.

Figure 2-21 The Die

Note: You can find the correct tap or die for the hole or screw to be threadedfrom drill and tap size tables. These must be used to get the correctthread size for the nuts and bolts in use. The tap has a chamfer at theend depending on its use. The taper tap is used to start the thread. Theplug tap is used to finish holes that go straight through. The bottom tapfor holes that only go some way into the material.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 21/20


2.10 THE POWER DRILL

A power drill rotates the drill bit at a constant high speed. This means holes can be

drilled faster and with less effort.

A typical workshop power drill is shown in Figure 2-22. Turn the handle to move therotating drill down through the material to be drilled. Note the safety features whichmust be used.

Figure 2-22 The Power Drill

Portable power drills run on either compressed air or electricity. These are designedto be held in the hand. The trigger switch, or speed control, is used to turn the drillon and off. The motor is in the body of the drill. The drill bit is inserted in the chuckand tightened with the chuck key. This prevents the bit from slipping (see Figure2-23)

Figure 2-23 The Portable Electric Drill

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s



July 1999- Rev.0

Page 22/20




July 1999- Rev.0

Page 23/20


2.11 PNEUMATIC IMPACT WRENCH

An air powered impact wrench uses an air motor and a special clutch. The clutch

changes the rotation to a series of fast, high powered impulses. It's used with asocket wrench to turn nuts and bolts. The impulses from the air wrench deliver fastsharp turns to the bolt head.

The motor of the impact wrench is reversible. Operating the motor in one directionwill tighten the bolt. Operating the motor in the other direction will loosen the bolt(see Figure 2-24).

Figure 2-24 Pneumatic Impact Wrench

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

2 -

B a s

i c h a n

d t o

o l s









UNIT 4 CRIMPING


M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





TABLE OF CONTENTS

Para Page


3.1 INTRODUCTION 4

3.2 TUBING 4

3.3 TUBE BENDING 5

3.4 BENDING TUBING TO SIZE 7

3.5 COMPRESSION FITTINGS 8

3.5.1 Making a Compression Fitting. 9

3.5.2 Remaking a Compression Fitting. 10

3.6 CONNECTORS 11

3.7 THREADS AND TEFLON TAPE 12

3.8 TUBING TOOLS 13

3.8.1 The Tubing Cutter 13

3.8.2 The De-burring Tool 14

3.9 TUBING INSTALLATION 15

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s






The student will be able to :

• State the minimum radius for a tubing bend.

• State the reasons for sloping process connections (impulse lines) and airsupply lines.

• List the problems which may happen when using compression fittings.

• Explain the use of the deburring tool

• Explain when and when not to use "Teflon" sealing tap.

• Explain the correct tubing fitting to avoid forcing fittings onto an instrument.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.1 INTRODUCTION

The most important mechanical work done by the instrument technician is laying outand connecting up tubing used for:

• Connections from the process to the instrument

• Pneumatic signal and air supply connections to the instrument.

This unit will explain the basic rules to be followed when carrying out tubing work.

3.2 TUBING

Tubing is seamless thin wall pipe. It is made of copper or stainless steel. It is easyto bend using simple hand tools.

Normally stainless steel tubing is used throughout the oil/gas industry. This isbecause it does not corrode easily. Copper tubing is mostly used for water heatingsystems. It is sometimes used in instrumentation workshops.

Low pressure systems, (for example in a training workshop), use plastic tubingwhich is cheap and easy to use.

Tubing comes in standard sizes; either metric or imperial. Tubing layouts should bemade all metric or all imperial. They should not be a mixture of both. The tablebelow shows the standard sizes (outside diameter) of instrument tubing.

Imperial (in inches)

1 /8, 3/16, 1 A 3/8, 1 /2, 5/8, 3/4, 7/8, 1

Metric (in millimetres)

3, 4, 6, 8, 10, 12, 15, 16, 20, 22 25

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.3 TUBE BENDING

When bending thin wall tubing it is important not to kink the tube. The radius of a

bend must be at least 2 1/2 times the diameter of the tube as shown in the examplein Figure 3-1.

Figure 3-1 Tube Bending

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





Hand tubing benders are made so that the radius of the bend is correct. The correctuse of the hand bender will make good bends automatically. A typical hand tubingbender is shown in Figure 3-2.

Figure 3-2 Hand Tubing Bender

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.4 BENDING TUBING TO SIZE

There is a good general rule for bending a piece of tubing to the correct length. You

should bend it at a point one tubing diameter less than the required length. Figure3-3 shows where you should bend a 1/2" diameter tube in order for it to reach therequired length of 9".

Figure 3-3 Making a 90

Bend

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





You need practice and judgement to make bends of less than 90°, The smaller theangle, the nearer the bending point to the required length. For example, in Figure

3-3 for a 45° bend, the bending point will be at 8 3/4” Remember it is safer to be too

long and cut a bit off the tubing. You must never force a short tube into aconnection. Tubing which has been strained to fit is dangerous. It stresses theconnectors, which may leak. When it is disconnected it can spring out of place andinjure people standing nearby.

3.5 COMPRESSION FITTINGS

Instrument tubing connections are done using compression fittings. You must notthread instrument tubing and use a nut to make a connection.

Figure 3-4 Section of a Compression Fitting

Figure 3-4 shows a section through a compression fitting. When the nut is tightenedthe twin ferrules are forced into the tube and against the sides of the connector.They make a metal to metal seal. This seal is very effective if the nut is tightenedcorrectly. It is good for pressures to at least 10,000 psi.

There are many manufactures of compression fittings, e.g. Parker, Swagelok etc.Some use only one ferrule (olive) but most use two. The ferrules in differentmanufacturers' fittings can not be changed with each other. You must -not mixdifferent types of compression fittings.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.5.1 Making a Compression Fitting.

Figure 3-5 Making a Compression Fitting

With reference to figure 3-5.

Step 1: Simply insert the tubing into the Swagelok tube fitting. Make sure that

the tubing rests firmly on the shoulder of the fitting and that the nut isfinger tight.

Step 2 Hold the connector tightly with a backup wrench. Turn the nut about1 1/2 turns (from finger tight). This is enough to seal the connectionproperly.

Don't over-tighten the nut

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.5.2 Remaking a Compression Fitting.

Figure 3-6 Re-making a Compression Fitting

Compression fittings can be re-made many times by the method shown in Figure3-6. The nut is re-tightened correctly by turning the nut about 1 1/2 turns from fingertight.

Don't over-tighten the nut!

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.6 CONNECTORS

You must choose the right connectors to connect tubing to an instrument, some

plants can use two quite different systems.

• Metric tubing with ISO pipe threads.

• Imperial (fractional), tubing with National Pipe Threads (NPT)

Manufacturers make connectors to fit all systems. They also. make connectors toconnect two different systems. Check which set of connectors are in use on a jobsite before doing any new tubing work. Figure 3-7 shows a few of the types ofconnector available (Swagelok).

Figure 3-7 Some Tubing Connections

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.7 THREADS AND TEFLON TAPE

Teflon tape is used to seal the gaps between threads. It is only used on "tapered

threads". This tape must not be used on threads Of compression fittings. The tapewill stop the metal to metal seal being made. This tape must not be used on parallelthread connectors. It will stop the connector from sealing on the bottom of the hole.

If Teflon tape is used, make sure the tape is wound in the right direction. When theconnector is screwed into the device the tape must be tightened onto the threads,(e.g. anticlockwise on a right hand thread). Put on Teflon tape carefully so that itcannot become loose and block air passages.

A typical example of the correct method of putting on Teflon tape is shown in Figure3-8.

Figure 3-8 Applying Teflon Tape

Note: Teflon tape is not as popular as it used to be, particularly on systems

running at high temperatures. In some plants special sealing compoundsmust be used instead of Teflon tape.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.8 TUBING TOOLS

A normal tubing tool kit has two special tools; the tubing cutter and the de-burring

tool.

3.8.1 The Tubing Cutter

Figure 3-9 The Tubing Cutter

Figure 3-9 shows a hand tubing cutter. The tubing is cut by the cutting wheel. Thisis rotated, by hand, round and round the tube. The adjustment screw is tightened asthe tube is cut. This keeps the wheel in contact with the tube.

The tubing cutter is easy to use and cuts tubing better than a hacksaw.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.8.2 The De-burring Tool

Figure 3-10 De-burring Tools

A tubing cutter will leave rough edges on the inside of the tube. These rough edges

are called burrs. They must be removed before a compression fitting is connected.These burrs can be removed with a round file but the easiest method is to use ade-burring tool. The deburring tool has many cutting edges. The tool is rotated byhand to remove the burrs on the inside of the tube (see Figure 3-10). Make sure thebits of metal are removed after de-burring. Any particles left inside the tubing willquickly block instruments connected to the tubing.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s





3.9 TUBING INSTALLATION

Air lines are usually fitted at a slight slope. This is to make sure that any moisture

which collects in the lines does not run into the instrument. The instrument issupplied from the top of the supply line. Moisture collects above the blow downvalve. The blow down valve is opened once a day to blow out any moisturecollected.

Process connections are made differently for gases and liquids. Tubing connectionsto a gas line are from above. The tubing slopes upwards to the instrument. Tubingconnections to a liquid line are from below. The tubing slopes downwards to theinstrument. Figure 3-11 shows the above points.

Figure 3-11 Tubing Installation

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

3 -

T u

b i n g s y s t e

m s






UNIT 1 WORKSHOP SAFETY AND TOOL CAR



UNIT 4 CRIMPING


M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

4 -

C r i m p

i n g





TABLE OF CONTENTS

,

Para Page


4.1 INTRODUCTION 4

4.2 CRIMPING 4

4.3 CRIMP CONNECTORS 6

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

4 -

C r i m p

i n g







• Explain the correct method of fitting a conductor into an insulated crimp.

• Explain why a rachet crimping tool should be used.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

4 -

C r i m p

i n g





4.1 INTRODUCTION

The aim of this unit is to explain the insulated crimp connector used ininstrumentation.

4.2 CRIMPING

This is a method of putting connectors onto electrical/instrument wires so that theycan be terminated into a terminal fitting. Crimps come in two basic types, insulatedand uninsulated.

Insulated crimps are made for small cable sizes. These are the crimps which arenormally used by the instrument technician. These crimps come in three standard

sizes shown by the colour code.

Table 1.

Colour Metric Standard Wire Gauge

Red 0.25 to 1.6mm2 22-18 SWG

Blue .00 to 2.6 mm2 16-14 SWG

Yellow 2.7 to 6.6 mm2 12-10 SWG

Figure 4-1 Insulated Crimp Connection

The conductor must fit the crimp terminal within the stated range, (see table 1). Youmust not use a cable which is too small for the crimp terminal if the cable is toosmall the crimps will not grip the conductor and the wire can be pulled out. Youmust not use a cable which is too big for the crimp terminals. If you force a cablewhich is too big into the crimp terminal, the conductor will be squeezed. Thisincreases the resistance and the connection will get too hot.

The crimps are connected to the conductor with a crimping tool. Insulated wiresshould be crimped twice. The first crimp holds the conductor. The second crimp

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

4 -

C r i m p

i n g





holds the cable (conductor and insulation). See Figure 4-1.





Crimping tools should be of the ratchet type. This means that the correct force mustbe applied before the tool can be released. Figure 4-2 shows a twin crimp ratchetcrimping tool. This tool should be used for insulated crimps.

Figure 4-2 Ratchet Crimping Tool

This is a ratchet tool for crimping red, blue/black and yellow insulated crimpconnectors. The tool has one fixed jaw and one movable jaw which makes the tooleasy to use. It may be held in one hand, so the other hand is free to hold theterminal and the wire. The built in ratchet system ensures a complete crimp is madeevery time. You need much less hand force than with normal tools. When acrimping action has been started the ratchet makes sure the tool cannot be openeduntil the jaws have completed the crimping action.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

4 -

C r i m p

i n g





4.3 CRIMP CONNECTORS

There are various types of connector that can be used, e.g. spade, ring, flat tab,

receptacle etc. Typical examples are shown in Figure 4-3.

Figure 4-3 Typical Insulated Crimp Connectors with Colour Cod

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

4 -

C r i m p

i n g









UNIT 4 CRIMPING


M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s





TABLE OF CONTENTS

Para Page

PRACTICAL TASK 1 3

PRACTICAL TASK 2 5

PRACTICAL TASK 3 6

PRACTICAL TASK 4 7

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 1

BASIC FITTING EXERCISE

Tools Required :

Engineer's Rule

Engineer's Set Square

Scriber, Centre Punch and Hammer

Power Drill and Drills

Taps and Dies

Drill and Tap Tables

Test Piece

Job Instructions

1) Make out the test piece as shown on the diagram.

2) Centre punch points ABCDEFGH.

3) Drill

A with a 3.3 mm drill

B with a 4.1 mm drillC with a 2.05 mm drill

D with a 2.6 mm drill

E with a 7/32" drill

F with a 33/64" drill

G with a 29/64" drill

H with a 17/64" drill

4) Using a tap and tap wrench (metric) make A and C 4mm and 2.5mmthreaded holes.

5) Using a tap and tap wrench (imperial) make E and G 1/4" and 1 /2" threadedholes.

6) Using a die and die wrench make screws to fit the tapped holes,i.e. 4mm, 2.5mm, 1/2" and 1/4"

7) Check that B is the clearance hole for the 4mm screw

Check that D is the clearance hole for the 2.5mm screw.

Check that F is the clearance hole for the 1/2" screw.

Check that H is the clearance hole for the 1/4" screw.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s





Test Piece Mild Steel 15mm Plate

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 2

DISASSEMBLY AND ASSEMBLY WORK

Tools Required

Ring, Open Ended, and Adjustable Spanners

Impact Wrench

Torque Wrench

Job Instructions :

1 Disassemble and assemble control valves, flanges etc. on the instructions ofthe instructor.

2) Assemble control valves, flanges etc. on the instruction of the instructor.

3) Remember to tighten a flange using the procedure as shown.

Tighten a little at a time using the sequence shown. Make sure the flange goesdown flat, not tipped to one side.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 3

TUBING EXERCISE

Tool Required :

Tubing bender, tubing cutter and deburring tool

Various tubing sizes

Various compression fittings

Job Instructions :

After the instructor has demonstrated the correct connection of tubing to a

compression fitting, practice making connections yourself.

Making the correct connection of tubing to a compression fitting is not as easy as itseems., When the instructor is satisfied with your fittings carry out the followingexercise.

Use 4 1/2" NTP 1/4 " tubing, male connectors, one union cross ' and variouslengths of A " tubing. Make the layout shown in the diagram.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s





PRACTICAL TASK 4

CRIMPING EXERCISE

Tool Required :

Various conductor sizes (to fit 1.5, 2 and 3.5mm connectors)

Various insulated connectors (spade, receptacle, pin, etc.)

Terminal strips (e.g. Klippon series)

Double crimp - rachet type crimping tools

Job Instructions

Crimp various conductors With different types of crimp connectors. Practice thecrimping technique until the work is satisfactory to the instructor.

Connect various conductors to a terminal strip. The layout of the connections will begiven by the instructor.

M o

d u

l e

N o .

1 1 :

I n s

t r u m e n

t c r a

f t p

r a c

t i c e

U n

i t N o .

5 -

P r a c

t i c a

l t a s

k s



July 1999- Rev.0

TRAINING MANUAL

INSTRUMENTATION

MODULE No. 12

INTRODUCTION TO PLC






UNIT 1 PLC FUNDAMENTALS

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





TABLE OF CONTENTS

Para Page


1.1 INTRODUCTION, 4

1.2 PLC SYSTEMS 4

1.3 RELAY SYSTEMS AND PLC COMPARISON 6

1.4 PLC SYSTEM EXAMPLES 8

1.4.1 The Allen-Bradley System 8

1.4.2 The Dual Redundant Emergency Shut Down PLC System 11

1.4.3 Triple Redundant PLC Systems 13

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l







• Explain the difference between PLC systems and the older relay systems.

• Explain the operation of a simple PLC ladder diagram.

• Explain the function of the Allen-Bradley PLC components.

• Explain using a block diagram the three basic PLC systems:

1. Single µP PLC

2. Dual redundant PLC

3. Triple redundant PLC

• Give examples of where the different types of PLC would be used.

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





1.1 INTRODUCTION

The aim of this unit is to explain the fundamentals of a Programmable LogicController (PLC). It will also act as an introduction to the main part of the course;practical work on a PLC unit.

1.2 PLC SYSTEMS

There are various manufacturers of PLC equipment. They all use different methodsfor sending data and make their diagrams to different standards. This means thatthe operating companies do not mix the different types of PLC systems. You cannotmix PLC systems when controlling a process. Some of the PLC systems used in thefields are:

The most common PLC systems are Allen-Bradley and Modicon which use theladder diagram method for PLC logic. This system is explained here so that you canpractice programming techniques on the Allen-Bradley training equipment availablein the workshop.

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





1.3 RELAY SYSTEMS AND PLC COMPARISON

The ladder diagram used has been explained using relays. Figure 1-2 shows a

block diagram of the overall system using relays. It is sometimes called aHARD-WIRED control system. When the control logic is installed it can only bechanged manually.

Note: The relay system is still preferred in some safety systems as it is verydifficult to check the software operation of a PLC for faults.

Figure 1-2 Block Diagram Relay Logic Control

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





A PLC collects inputs and distributes outputs in the same way as a relay logiccircuit. However, the relays are replaced by a microprocessor which is programmedto provide the switching logic. Figure 1-3 shows a typical PLC block diagram based

on Allen-Bradley.

Figure 1-3 Block Diagram Programmable Logic Control

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





1.4 PLC SYSTEM EXAMPLES

1.4.1 The Allen-Bradley System

Figure 1-4 Main Components of Allen Bradley PLC

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





Figure 1-4 shows the major components of an Allen-Bradley PLC. It consists of thefollowing units.

1) Main Processor Unit.

• This units provides the following functions

• The system µP and RAM.

• EEPROM memory compartment. An EEPROM is normally added asa back-up to hold the RAM programme in case of system failure.

• Input conditioning for 10 inputs with status indicators.

• 6 separate outputs with status indicators.

• Battery compartment with lithium battery. This battery supplies D.C.power to hold the RAM data if the mains supply is lost.

• Communication port so that the processor RAM can bereprogrammed.

The unit is powered by a standard single phase supply WAE: 240V-50 Hz).This supply is connected to the incoming line terminals.

2) Expansion 1/0 unit.

This unit is connected to the main processor unit by a cable. It uses theconnections shown to provide increased 1/0's. This provides an extra 10inputs and 6 outputs. There are status indicators for each 1/0. This unit getsd.c. power from the main processor unit. A d.c. power indicator is providedto show that this unit is powered -correctly.

Note: Allen-Bradley also supply a hard-wired relay expansion unit.

This unit is used if higher current switching is required. Maximum 2.5Acontinuous when switching either 240V a.c. or 24V d.c.

3) Pocket Programmer.

This unit has a keyboard and display panel. It is used to programme(configure) the required logic operations. This will be used in the workshopwhen you try some simple programming techniques.

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





The Allen-Bradley system described is one of the simple single µP types. It is usedfor

a) Controlling a single process (e.g. pump starting, ship loading sequencesetc.)

b) Larger processes which have no effect on plant safety. (Therefore they mustbe cheap, e.g. fire detector systems for accommodation units etc.)

c) As a back-up for a large safety system. (E.g. to operate a shutdown if theemergency shut-down button is pressed or a fire alarm if the "break glass"unit is operated).

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l





1.4.2 The Dual Redundant Emergency Shut Down PLC System

The most important feature of an ESD system is that it must only operate when

there is a failure in the plant. There are two main problems if the ESD equipmentfails. The first problem is the high cost of lost production. The second problem isthat if the ESD equipment keeps failing the operations staff by-pass the system inorder to keep the plant running. The dual redundant PLC system reduces thechance of an ESD system shutting down the plant because of ESD equipmentfailure. However, it ensures the plant is shut-down when there is a failure in theplant. Figure 1-5 shows the basic block diagram of a fully redundant PLC system(e.g. the new Allen-Bradley PLC-5 series and ICS).

Figure 1-5 Dual Redundant PLC System

M o

d u

l e

N o .

1 2 :

I n t r o

d u c

t i o n

t o P L

C

U

n i t N o .

1 -

P L C F u n

d a m e n

t a l




OPERATION

ipedex instrumentation training modules

Documents