By-Sheik Rema(5050)

Abhigya Arvind(5051)Abhijit Sengupta(5053)

AEIE DepartmentAsansol Engineering College

PROGRAMMABLE LOGIC CONTROLLER (PLC)

PLC and its Applications

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

HISTORY OF PLC

First PLC systems evolved from conventional computer in 1960s. These PLCs were installed in automotive plant

In 1972, using microprocessor chip, computer power In 1980s Use of PLC was exponentially increasing.

The growth of PLC application is shown 1.4 B

in figure. 80 M

1978 2009

Major Components of a Common PLC

PROCESSOR

POWERSUPPLY

I MN O P D U UT L E

O M U OT DP UU LT E

PROGRAMMING DEVICE

From SENSORS

Pushbuttons,contacts,

limit switches,etc.

ToOUTPUT

Solenoids, contactors,

alarmsetc.

OVER VIEW OF PLC SYSTEM

A PLC system has four major units:

1. Central Processing Unit: It consists of three parts

(i) Microprocessor: To perform mathematical and logical

operations

(ii) Memory: To store data and information

(iii) Power supply: To convert AC to DC for computer

operation.

2. Programmer/monitor: It communicates with the circuit

of PLC: There are three types of Programmer/monitor

(i) Hand held terminals: Input supplied through a membrane key pad and display is LCD

(ii) Industrial terminals: Input supplied through a Key board and display unit is CRT

(iii) Personal computer: Input supplied through a Key board and display unit is CRT

3. I/O modules: (i) The input modules process electrical signal

from sensors(ii) The output module sends the signals to

activate relays, switches, motors etc.

8

I/O Module

DC INPUT MODULE

OPTO-ISOLATOR

IS NEEDED TO: Prevent voltage transients from damaging the processor.Helps reduce the effects of electrical noise

CurrentLimitingResistor

FROM INPUTDEVICE

USE TO DROP THE VOLTAGE TO LOGIC LEVEL

Buffer, Filter, hysteresis Circuits

TOPROCESSOR

INPUT MODULE LAYOUT

120 v

To CPUSENSOR/

SWITCH

5

I/O Module

DC / AC OUTPUT MODULE

OPTO-ISOLATOR

IS NEEDED TO: Prevent voltage transients from damaging the processor.Helps reduce the effects of electrical noise

FROM PROCESSOR

TTLCircuits

AmplifierRELAYTRIACX’SISTOR

TOOUTPUTDEVICE

PLC OUTPUT MODULE LAY OUT

FROMCPU

TRIGGER

CONTROL

AC LOAD

4. RACKS AND CHASSIS

Racks: It is used to mount the PLC partsChassis: It is the enclosure on which covers

Logic elements

11

PLC

INPUTS

OUTPUTS

MOTOR

LAMPCONTACTOR

PUSHBUTTONS

PLC Applications

Dispensing oil level controller

Switch and lamp circuitConsider the following

circuit and PLC program: When the pushbutton switch is unpressed, no power is sent to the X1 input of the PLC. Following the program, which shows a normally-open X1 contact in series with a Y1 coil, no "power" will be sent to the Y1 coil. Thus, the PLC's Y1 output remains de-energized, and the indicator lamp connected to it remains dark.

Cont. If the pushbutton switch is

pressed, however, power will be sent to the PLC's X1 input. Any and all X1 contacts appearing in the program will assume the actuated (non-normal) state, as though they were relay contacts actuated by the energizing of a relay coil named "X1". In this  case, energizing the X1 input will cause the normally-open X1 contact will "close," sending "power" to the Y1 coil. When the Y1 coil of the program "energizes," the real Y1 output will become energized, lighting up the lamp connected to it:

Cont. In the following illustration, we

have the altered system shown in the state where the pushbutton is unactuated (not being pressed:

In this next illustration, the switch is shown actuated (pressed):

Example Continued

Motor control

Thank you