Presentation OnProgrammable Logic Controller

(PLC)By: -ROSHIT KADIRU7TH SEM EE

What Is Programmable Logic Controller?

A programmable Logic Controller (PLC) is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures.

• Cost effective for controlling complex systems.• Flexible and can be reapplied to

control other systems quickly and easily.

• Computational abilities allow more sophisticated control.• Trouble shooting aids make

programming easier and reduce downtime.

• Reliable components make these likely to operate for years before failure.

• Small physical size, so shorter project time.•Ease in documentation.

Advantages of PLC

Architecture of PLC

Input Module

Output

Module

Central Processing Unit

(CPU)

Power Supply

Program-ming

Device

Push Button

Push Button

Light

Programming Device

Architecture of PLCInput Module : It senses the presence or absences of an input signal at each of its input terminal.

Output Module : The output module operates the opposite manner from the input signal. A DC signal from the CPU is converted through each module section to a usable output voltage.

Central Processing Unit (CPU) : It is the brain of every computer. CPU carries out arithmetic and logical operations.

Programming Device : A programming device is a computer in which programming is done and then by using data cables the program is downloaded into the PLC. For connecting to the PLC “RC-232C” cable is used.

RS-232C Cable

Scan Cycle of PLC

Read input

Run Program

Adjusts output

The Scan is a continuous

and sequential

process

• There are three types of PLC.1. Unitary PLC

Types Of PLC

2. Modular PLC

3. Rack Mounted PLC :

It contains every feature of a basic system in one box. They are attached to the machine being controlled.

Advantages:1. Less scanning time2. Fixed versions are usually small, have

less memory so cost in less .3. Less troubleshooting time so less

downtime. Disadvantages :1. A limited number of inputs and

outputs.2. It is not suited for future expansion.3. If part of the unit fails, it will take much

time and effort to repair, and the entire unit may need replacing.

Unitary PLC

It s a range of modules that slot together to build up a system. The basic are the power supply, the main module containing the CPU, the input and output module.

Advantages:1. Great flexibility in choice of modules. Modules

can be easily installed or removed without affecting other modules

2. The main advantage is that more Input and output terminals can be expanded.

Disadvantages :1. Scanning time increases with the increase in

input and output modules.

Modular PLC

This is similar concept to the modular design but the modules are on standard cards that slot into a standard rack inside a cabinet. These are flexible and allow expansion of the system.

Rack Mounted PLC

What happens when line voltage comes in contact with the low

voltage DC section of PLC?

6

5 4

3

2

18

7

Relay Coil

NO

NC

NO

NC

24 V

230 V

Plug in base of relay

PLC

What Happens Then????

What Happens if the wires are wrongly

connected

What happens when line voltage comes in contact with the low

voltage DC section of PLC?

6

5 4

3

2

18

7

Relay Coil

NO

NC

NO

NC

24 V

230 V

Plug in base of Relay

PLC

Optical Isolation

It means there is no actual electrical connection between the input device and the processor. This eliminates any possibility of the input line voltage from coming in contact with and damaging the low voltage DC section of the processor. It prevents any unwanted voltage from the i/o section of the processor.

OFF

Micro -Processo

r

Input Signal

1

+5 V

Push Button

Photoelectric Switch

Working of Optical Isolation

LED

Programming Languages of PLC

There are “5” programming Languages in PLC

1. Ladder Diagram (LD)

2. Functional Block Diagram

(FBD)

3. Structured Text (ST)

4. Instruction List (IL)

5. Sequential Function Chart

(SFC)

Ladder Diagram (LD)

It is a graphical programming language. It is programmed with simple contacts that simulated the opening and closing of relays it has been expanded to include function such as counters, timers, shift registers and math operation.

Ladder Diagram (LD)Contacts and coilsExamine if closed

Examine if open

It works as normally open switch in a ladder program. If it is ON, the contact will close and allow power (logic) to flow from left to right. If the status is OFF (logical 0), the contact is Open, power (logic) will NOT flow from left to right. It works as normally closed switch in a ladder program, and it works exactly opposite to that of the examine if closed.

Normally open coilThis can be used to represent any discrete output from the control logic. When "solved" if the logic to the left of the coil is TRUE, the referenced output is ON (logical 1).

Ladder Diagram (LD)Timer

•The Timer On Delay instruction begins to count time base intervals when rung conditions become true. As long as rung conditions remain true, the timer adjust its accumulated value (ACC) each evaluation until it reaches the preset value (PRE). The accumulated value is reset when rung conditions go false, regardless of whether the timer has timed out.

Timer On DelayTimer T4:1Time Base 1.0Preset 100Accum 0

TON

(

(

(

(EN

DN

Ladder Diagram (LD)Counter

•Increments the accumulated value at each false to true transition and retains the accumulated value when the instruction goes false or when power cycle occurs.•The CTU is an instruction that counts false to true transition. When this transition happens the accumulated value is incremented by one count.•A CTU accumulation is reset by the RES instruction.

Count UpCounter C3:0Preset 10Accum 0

CTU

(

(

(

(

CU

DN

AND operation using Ladder Diagram (LD)

(

(

Switch 1 Switch 2 Light

Switch 1 Switch 2

OFF OFF

Light

Switch 1

Switch 2

Output

0 0 0

1 0 0

0 1 0

1 1 1

Truth Table

Example of Forward and Reverse motor starter

Example’s Ladder Diagram (LD)

Example’s Ladder Diagram (LD)

(

(

((

M1

M2

Forward

M1

M1

M2

Reverse

Stop

M2

Normally OpenPush button

Normally OpenPush button

Normally ClosedPush button

Thank You