INSTRUMENTATION AND CONTROL

(MCT 3224)

INTRODUCTION TO INSTRUMENTATION

Hasmawati Antong

Lecturer,

Department of Mechatronics Engineering,

International Islamic University Malaysia

Content

Introduction to instrumentation and measurement

Types of instruments

Functions of instruments

Principle of measurement

Measurement systems

Element of process control and instrumentation

Application of instrumentation

Summary

Introduction to instrumentation and

measurement

Instrumentation comprises of scientific activities and

technologies that are related to measurement.

It is a link between physical, chemical and

biological phenomena and their perception by

human

Instrumentation serves to stimulate scientific

knowledge in the junction between theory and

experimental practice

Instrumentation is the science of measurement and

control

Introduction to instrumentation and

measurement

It can be used to refer to two elements:

1) The field in which instrumentation technicians and

engineer work

2) The available methods of measurement and the

instrument which facilitates it

The primary purpose of instrumentation in industrial

manufacturing is to aid the economics of industrial

operation by improving:

1) the quality of the product

2) the efficiency of the production

Introduction to instrumentation and

measurement

Instrument is a device that transforms physical

variable of interest (measurand) into a form that is

suitable for recording (measurement)

Measurement means to employ a standard system

of units by which the reading from one instrument

can be compared with another

Measurand Length

Measurement meter

Types of Instrument

1) Analog instrument

A deflection type instrument

Gives output that varies continuously as the quantity

being measured change

Example:

Types of Instrument

2) Digital instrument

Display the decimal form of the value of the

quantity being measured

The output varies in discrete steps

Example:

Types of Instrument

3) Passive instrument

The output is produced entirely by the quantity

being measured

Example:

• A pressure-measuring device

• Pressure of fluid movement

of pointer against a scale

• No other energy inputs to the

system

Types of Instrument

4) Active instrument

The quantity being measured modulates the

magnitude of an external power source

Example:

• Float-type petrol tank level indicator

• Change in petrol tank level moves potentiometer arm

• Output signal shows proportion of the external voltage source across the potentiometer

Function of Instrument

The common purpose of instruments are to supply

information about the variable quantity being

measured.

Basic functions of instruments:

1) Indicating

2) Recording

3) Controlling

Functions 1) & 2) are for general test instruments

Functions 3) only applicable for industrial process

instruments

Principles of Measurement

Input to the measurement system is the actual value

Output from the measurement system is the measured

value

Measurement System

Measurement system refers to all the software and

hardware that lead from the measured variable to the

processed data.

Measurement System

Sensing element (sensor) : device in contact with the

measured process and giving output depends on the

quantity being measured

Signal conditioning element : takes output from sensor

and converts it to a form suitable for processing

(amplifiers, filter)

Measurement System

Signal processing element : takes output from the

signal conditioner and performs

analysis/transformation (ADC, spectral analyzer)

Data presentation : computer display, graphs,

indicator, gauges, etc

Elements of Process Control and

Instrumentation

1. Process (plant)

Consists of complex assembly of phenomena that relates to some manufacturing sequence

Contain the variable to be controlled

Single-variable process (eg. Control only temperature)

Multi-variable process (eg. Control temperature and humidity)

2. Measurement

To get information about the variable to be controlled

Sensor is used to perform the measurement and also energy conversion (eg. Temperature sensor convert temp. to voltage)

Elements of Process Control and

Instrumentation

3. Controller / Error detector

Used to examine the error and determine the action to be taken (if any)

Error is obtain from the difference between the measured value and the reference value

Its operation usually performed by microprocessor-based computers

4. Setpoint

Refers to the reference value set by user

5. Control Element

The element that exerts the change in the controlled variable

Elements of Process Control and

Instrumentation

Block diagram of a refrigerator process-control loop

Elements of Process Control and

Instrumentation

1) Process the refrigerator and all its contents

2) Measurement a sensor in the refrigerator to measure the internal temperature

3) Controller / error detector controller (relay, PI, PID) to turn on the compressor and fan

4) Setpoint determined by set knob setting

5) Control element compressor and fan circulate the cold air

Application of Instrumentation

1) Regulating trade

Achieved by applying instrument to measure physical quantities such as length, volume and mass in terms of standard units

2) For monitoring

Measurement information allow us to take some prescribe action accordingly

For instance, temperature monitoring in vaccine storage allow us to decide either to increase the cooling rate or not

Applicable in our daily live or to control some industrial process

Application of Instrumentation

3) As part of automatic feedback control system

Elements of a simple closed-loop control system

Summary

Instrumentation involves measurement process and control process

Instrumentation is very important in engineering field because it allows us to measure, observe, control and keep record of the physical process that we are working with.