Plc Programming

PROGRAMMABLE LOGIC CONTROLLER (PLC)

PLC = AUTOMATION

1.1 Three Factors of Automation What is automation? Moving the machine automatically in an Industrial Plant is automation. Ex. Putting a cap (lid) on a bottle in a running conveyor put a lid…

Five Senses

Brain

Visual, feeling, taste, hearing, smell

Judgment

Muscle Action

1. Visual conforms that the bottle comes on the conveyor

INPUT

2. Judgment decides to put lid

CONTROL

3. Get a lid to put it on a bottle

OUTPUT

These are called 3 factors of automation

INPUT (X)

CONTROL

OUTPUT (Y)

Micro switch

Relay

Lamp

Limit switch Sensors

Timer Counter

Buzzer Motors

Push button switch

Thermostat

Cylinder

1.2 External Input / Output Signal and Input / Output Number

-An input number is the number of hexadecimal which begins from 0.

X – indicates as the input signal - (X01-X09 and XOA-X0F) Y- indicates as the output signal - (Y01-YO9 and Y0A-Y0F)

1.3 UNIT COMPOSITION OF A PLC MODULE

A block type example explains the composition of an actual sequencer.

Power supply unit

CPU unit

Input / output unit

Base unit

Chapter 2 Components and functions of PLC 2.1 Components and functions of PLC

Input

Memory

CPU

Output

Power

Peripheral tool

Name

Power

Functions

Transforms the external power supply to direct power

Name

Functions

Input

Input devices were connected here. It reads the signals from the Photoelectric sensor devices and transfer them to CPU.

Micro switch

Photoelectric sensor

CPU

Reads the signals from the input part, judge them according to the program order, and sends the signal to the output part.

program

Memory

memorize the program

Name

Functions Lamp

Output

Peripheral tool

Output devices are connected here. It receive the signals from CPU and conveys them to output devices.

Peripheral tool includes programming console and support software.

Buzzer

How the system works Push the switch to run the motor.

Memory

①Push the switch

⑤Motor runs. ③What is the next step after the switch was pushed? Program of the memory tells me to move the motor.

②The switch has been pushed

④Move the motor.

Chapter3: Ladder chart Schematic/Ladder Diagram

Conventional

PLC Program

L1

L2 PB1

PB2

L1

L2 X1

M1

M1

M1

M1 L1

M1

X2

Y2

M1

All input Signals were assigned as X and Output signal as Y

3.1 ON circuit or Normally Open (NO)

A contact

push PB1 While the pushbutton is pushed, the lamp shall keep on.

LAMP

PB1 or X1

LAMP or Y1 Y1

In this diagram, if you release the button the lamp will return back to OFF mode.

3.2 OFF circuit or Normally Close (NC) B contact

push PB1 While the pushbutton is pushed, the lamp shall keep off.

LAMP

PB2 or X2

LAMP or Y1 Y1

In this diagram, if you release the button the lamp will return back to ON mode.

3.3 AND circuit (series) PB1 AND

PB2

Turn on the lamp when both PB1 and PB2 are pushed.

LAMP X1

X2 Y1

In this diagram, PB1 & PB2 shall push together to turn the lamp ON.

3.4 OR circuit (parallel) OR

X1 Y1

When either PB1 or PB2 is ON the lamp shall be ON

PB1 (X1)

PB2 (X2)

LAMP (Y1)

X2

Chapter 4. Programming and Time Chart

ON AND OFF TIME CHART

Common Symbols  –M Coil  – T Timer Input -X Output - Y Counter - C

Input A Input B

Output Y

WHEN INPUT A IS ON, OUTPUT A WILL BE ON. WHEN INPUT B IS ON, OUTPUT A WILL BE OFF.

Ladder Diagram

L1

X1

L2

X2 M1

M1

Y1

M1

ON DELAY TIMER

Input A

Input B

t=5sec

Output Y

WHEN INPUT A IS ON, AFTER 5 SECS., OUTPUT A WILL BE ON. WHEN INPUT B IS ON, OUTPUT Y WILL BE OFF.

Ladder Diagram

L1

X1

L2

X2 T1 k50

T1

M1

T1 Y1

M1 END

End