the importance of electrical ladder diagram...

THE IMPORTANCE OF ELECTRICAL LADDER

DIAGRAM in PLC PROGRAMMING AND

APPLICATIONS Gamaliel F. Itao, PEE

Programmable Logic Controller

• Defined as the first digital computer used for automation of industrial processes, such as control of machines in factory assembly lines.

• It is the basic building block of Industrial Automation and is the heart of the control system.

PLC Composition

• Progmmable Logic Controller is like typical PCs, it has two components, namely hardware and software.

• The hardware consists of the CPU, memory, input and output communication modules.

PLC SOFTWARE

• The software is composed of the languages or programs that run the hardware and perform certain functions.

• To name some languages , they are the ff: 1. Basic statement list

2. Mnemonic

3. Function block

4. Structured text

5. Ladder Diagram

Ladder Diagram

• Is the most common language and popular and which is even considered as the standard language of the PLC.

• It is similar to the hardwired Electrical Relay Ladder Diagram. The Control Logic is portrayed in the simple logic circuits of series, parallel and its combination series –parallel and the parallel –series connection.

Relay Ladder Diagram

• Is the foundation of the Programmable Ladder diagramming which can easily be traced by plant electricians and maintenance personnel.

PLC Ladder

• For this reason, PLCs are still dominant in the automated manufacturing control systems because of the existence of PLC software Ladder Diagram.

• Plant electricians are used to electrical relay ladder as it can easily be learned compared to the scripted languages of non PLCs.

Control Engineering Magazine

• Published in the USA reported that PLCs now control 95% of plant manufacturing and equipment as well as process operation control systems in the US.

• Only 5 % goes to non PLC and dedicated control operations such as Robotics and Process automation controllers(PACs).

PLC APPLICATIONS

Conventional Control Panel (Waste Water Pumping Station)

Old Panel Indicators

Conventional Control System

Industrial Controls Corporation Phone: (632) 687-4814 Fax: (632) 687-2443

www.IndustrialControlsCorp.com

Industrial Controls Corporation Phone: (632) 687-4814 Fax: (632) 687-2443

www.IndustrialControlsCorp.com

Equipment

Equipment

PLC – Scada Based System

SCADA BASED PC MONITOR/CONTROL

Panel Wirings for a

5MW Generator (Rehab)

PLC Based Purifier System

PLC / HMI

PLC – HMI Based Process Monitoring System

SUB CONTROL SYSTEM PRIMARY CRUSHER

INSTRUMENTATION AND CONTOL SYSTEMS ARCHITECTURE

PRIMARY CRUSHER AND AUXILLARIES

HMI-OPERATORS WORK STATIONS

DISTRIBUTED I/O GYRATORY CRUSHER & AUXILLARIES

DISTRIBUTED I/O PAN FEEDER & WEARING CONVEYOR

DISTRIBUTED I/O CONVEYOR NO. 1

LINK TO STC CONTROL SYSTEM

SUB CONTROL SYSTEM SEC & TER CRUSHERS

INSTRUMENTATION AND CONTOL SYSTEMS ARCHITECTURE

STC-SCREENING-COS-CONVEYING-FOB

HMI-OPERATORS WORK STATIONS

HMI-OPERATORS WORK STATIONS

HMI-ENGINEERING WORK STATIONS

SUB CONTROL SYSTEM PRIMARY SCREEN

SUB CONTROL SYSTEM SCREENING PLANT

SUB CONTROL SYSTEM CONVEYING

SUB CONTROL SYSTEM FOB

DISTRIBUTED I/O PRIMARY SCREEN

DISTRIBUTED I/O SCREENING PLANT

DISTRIBUTED I/O CONVEYING

DISTRIBUTED I/O FOB

DISTRIBUTED I/O SEC & TEC CRUSHER

CONTROL SYSTEM

Control System

I. Open Loop System

INPUT LOGIC OUTPUT

-Pushbuttons

-Limit Switches

-Level Switches

-Flow Switches

-Relays

-Timers

-Counters

-Motors

-Solenoid valves

-Lamps

PLC

A typical Control System (electromechanical)

CONTROLLER

CNT

ELECTRONIC CARDS

RESET

COUNTER

CLOCK

TIMER COIL

LATCHING COIL

COIL

RELAY

8 8 8

INPUT DEVICES

PUSHBUTTON

LIMIT SWITCH

THUMB

WHEEL

SWITCH

LEVEL SWITCH

FLOW SWITCH

OUTPUT DEVICES

HEATER

8 8

MOTOR

SOLENOID

LED

DISPLAY

HEATER

LAMP

II. Closed Loop (Feedback) System

Control Unit Final Control Element

Process Variable

Measuring Element

Set Point

Error

Measured Variable

Primary Element / Transducer

Pressure

Level

Temperature

Flow

Control System

_ +

1. Process Variables - a quantity that can be measured in an industrial process. This maybe regulated or simply measured. Example: Pressure, Level, Temperature, Flow 2. Measuring Element – the element which converts a measurable variable into a form or signal that the controller can understand. Example: Transmitter - A transmitter sense the actual value of a system

and transforms the value to a standardized signal - 4-20 mA is common for analog signals - as input for the control system.

Controller

3 Final Control Element – the final device which actually control the process flows in response to controller output. Example: 1. Control Valves 2. Inverter 3. I/P Converter 4. Heater

PLC Based Process Control Unit: Typical Configuration

INSTRUMENTATION LOOP

UNDERSTANDING ELECTRICAL

CONTROL CIRCUITS: (RELAY LADDER )

WHAT IS A RELAY? A relay is an

electrically operated

switch.

The Functions of a Relay

1. Conversion

2. Multiplication

3. Memory

4. Amplification

R

L

1. Conversion

3. Memory Latching Circuit

L1

R

L2

2. Multiplication

L1

R1 R1

(+) (-) 3. Amplification

M

L1 L2

OFF ON

R1

R1

R1

R1

R1

R1

PB PB

ON OFF

220 V

Types of Control Logic Circuits

I. Series

End to end connection of contacts

Used in interlocks

Processing logic action is AND (.)

L1 (+) L2 (-)

S3 S1 S2

Out 1

Logic Statement

S1 . S2. S3 = Out1

II. Parallel

Both ends of contacts are connected

Used in different location or multiple contacts provide some signal

Process action is OR (+)

S1

S2

S3

Out 1

Logic Statement

S1 + S2 + S3 = Out1

III. Series-Parallel Circuit

Contacts in series and connected parallel

S1 S2

S3 S4

Logic Statement

(S1 . S2) + (S3 . S4) = Out1

Out 1

IV. Parallel-Series Circuit

S1 S2

S4 S3

Out 1

Logic Statement

(S1 + S3) . (S2 + S4) = Out1

Exercise:

Simplify the circuit. What is the type of circuit?

S1 S2

S5 S3

S4

Out 1

Answer:

Simplifying using KISS (Keep It Simple and Safe) concept. The flow of circuit in the

1) Circuit is from left to right (Line 1 to Line 2) (Pattern 1-2)

2) Circuit is from top to bottom and bottom to top. (Pattern 3-4)

S1 S2

S5 S3

S4

Out 1

L1 L2

L1 L2

Out 1

S1 S2

S3 S4

S5 S4 S1

S3 S4 S2

What type of circuit is it now?

Input = Output

2 TYPES OF SEQUENTIAL CIRCUIT DESIGN TECHNIQUES

1. ELECTROMECHANICAL SEQUENTIAL CIRCUIT USING RELAYS

2. PLC BASED DESIGN TECHNIQUE

1. VECTOR REPRESENTATION

CYLINDER FORWARD OR

CYLINDER RETRACT OR

2. CYLINDER FORWARD (+)

CYLINDER REVERSE (-)

A+B+A-B-

REPRESENTATION OFMOTION SEQUENCE OF MECHATRONICS OUTPUT DEVICE

A

B

1 2 3 4 5

MOTION STEP DIAGRAM

Graphical Representation

EXERCISE 2 ELECTRO-PNEUMATIC

DOUBLE ACTING CYLINDER

DOUBLE ACTING CYLINDER

4/2 WAY DIRECTIONAL CONTROL VALVE.

DOUBLE SOLENOID VALVE

A+ A-

A+ A-

A a0 a1

BASIC PNEUMATIC/HYDRAULIC CYLINDER CIRCUIT

RIGHT TRAVELLING

LOWERING

(DOWN)

B

A-POINT B-POINT

A

C

LEFT TRAVELLING

(UP)

RAISING

BASIC PICK AND PLACE ROBOT EXAMPLE

WORK

UNCLAMP

CLAMP

MOVE

B

A-POINT B-POINT

A

C

BASIC PICK AND PLACE ROBOT EXAMPLE C+

BACK

A+

B

A-POINT B-POINT

A

C

BASIC PICK AND PLACE ROBOT EXAMPLE A-

BACK A+C+

B

A-POINT B-POINT

A

C

BASIC PICK AND PLACE ROBOT EXAMPLE B+

BACK A+C+A-

A

C

B

A-POINT B-POINT

BASIC PICK AND PLACE ROBOT EXAMPLE A+

BACK A+C+A-B+

A B

A-POINT

BASIC PICK AND PLACE ROBOT EXAMPLE C-

C

B-POINT

BACK

A+C+A-B+A+

28

A B

A-POINT

BASIC PICK AND PLACE ROBOT EXAMPLE A-

C

B-POINT

BACK

A+C+A-B+A+C-

A B

A-POINT

BASIC PICK AND PLACE ROBOT EXAMPLE B-

C

B-POINT

BACK

A+C+A-B+A+C-A-

B

A-POINT B-POINT

A

C

BASIC PICK AND PLACE ROBOT EXAMPLE BACK

A+C+A-B+A+C-A-B-

Design Technique 1

STEPS USING SIMPLIFIED ELECTRICAL DESIGN

TECHNIQUE

1. Analyze work process and come up with its abbreviated notation for the representation of motion sequence.

Example 1: Bending A+ A- B+ B-A- 2. Divide the sequence into minimum number of groups

according to basic rules, (like:no letter must appear more than once in any group)

Example 2: A+ / A- B+ / B-

CYL A CYL B

SOL 1 SOL 2 SOL 3 SOL 4

CYL B

CYL A

A+A-B+B- a0 a1 b0 b1

EX.2 ELECTROMECHANICAL

3. Appropriate signals involved

Appropriate Input

a1 b1

Ex.3: A+/ A- B+/ B-

start a0 b0

GRP R1 GRP R2

NO. OF RELAYS = NO. OF GROUPS+ 1 AUXILIARY RELAY

= 3 +1

= 4

NO CONTACT

OF OWN GROUP

RELAY

Rx Ry

Rx

LAST LS OF

PREVIOUS

GROUP

NC CONTACT

OF NEXT GP

RELAY

GROUP

RELAY

LATCH CIRCUIT

(GROUP RELAY CIRCUIT)

4. Appropriate a group relay for each group (a latch circuit)> (Rx=(Ls+Rx) RY) which is turned on by change over limit switch (last limit switch of previous group) and turned off by opening of the NC contact of control relay on the next group.

EX. 4

R1

R2

R3

R4

SOL 1

SOL 2

SOL 3

SOL 4

R2

R3

R1

R1

R2

R2

R4

R3

R3

R3

start stop

a1

a0

b0

b1

A+/A- B+/B- START

a1

a0

b1

B0

NO. OF RELAYS = NO. OF GROUPS+ 1 AUXILIARY RELAY

= 3 +1 = 4

A+

A-

B+

B-

8 8 8

INPUT DEVICES

PUSHBUTTON

LIMIT SWITCH

THUMB

WHEEL

SWITCH

LEVEL

SWITCH

FLOW

SWITCH

OUTPUT DEVICES

HEATER

8 8

MOTOR

SOLENOID

LED

DISPLAY

HEATER

LAMP

SOFTWARE CIRCUIT

PROGRAMMABLE CONTROLLER

DESIGN TECHNIQUE

PLC BASED:

6 DESIGN STEPS IN PLC BASED SYSTEM

STEP I. SCHEMATIC OR POWER DIAGRAM

Exercise 1 FORWARD/ REVERSE SCHEMATIC DIGRAM OF 3-PHASE MOTOR

M

STEP II.CONTROL DIAGRAM (RELAY DIAGRAM) OF EXERCISE 1

PB FORWARD

PB STOP

REV

FWD

FWD

REV

FWD

REV

100 01

100 02

STEP IV. PLC DIGRAM

1 3 10002

10001 10001

10002

3 2

STEP III. INPUT/OUTPUT ASSIGNMENT OF EXERCISE 1

PB FWD –1 FWD-10001

PB REV - 2 REV-10002

PB STOP- 3

STEP V. (BOOLEAN/MNEMONIC STATEMENTS) OF EXERCISE

(Optional : Automatic View : Lad <>Mnemonic

ADDRESS/STEP INSTRUCTION DATA 0 LD 1

1 OR 10001

2 ANDN 3

3 ANDN 10002

4 OUT 10001

5 LD 2

6 OR 10002

7 ANDN 3

8 ANDN 10001

9 OUT 10002

10 END

STEP VI. PLC LAY-OUT

CENTRAL PROCESSING UNIT

1 2 3

FWD

REV

INPUT MODULE OUTPUT MODULE

PS

+ -

Com(-)

220 Vac / 24 Vdc

OUT 1

OUT 2

Com L1 L2

FREE TRAININGS: PLCs, MECHATRONICS NC II

and INSTRUMENTATION NC II

Thru TESDA

Training for Work Scholarship Program ( TWSP)

MECHATRONICS TECHNOLOGIES CORP. ( MTC )

Tel. 9283307 and 9286297

INDUSTRIAL CONTROLS

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GLOBAL TECHNOLOGIES MAINTENANCE

SYSTEM

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THANK YOU

Gamaliel F. Itao, P.E.E.,M.Ent

President, ICC-MTC-GTMS

Email: jimmy.itao@gmail.com