plc exercises

EXERCISES

Example (Central Heating)

Consider a central heating system with the

following features :

The boiler is thermostatically controlled and

supplies the radiator system in addition to a hot

water tank.

Pumps are used to supply hot water to either or

both the radiator and the tank according to the

desired sensors.

The whole system is controlled by a clock to

operate a certain time a day.

Boiler Temp.

sensor

Motorized

Pump

M1

M2

Boiler

Motorized

Pump

Radiator

System

Room

Timers

Hot water tank

Temp. sensor

Hot water

tank

The power circuit for the central heating

system is :

Stop

Run

Clock

Boiler sensor

Room sensor

Tank sensor

Power

Ou

tp

uts

Boiler

M1

M2

In

pu

ts

The ladder & IL program for the central heating

system using Mitsubishi PLC is :

Inputs :

X400 Clock

X401 Boiler sensor

X402 Room sensor

X403 Tank sensor

Outputs :

Y430 Boiler

Y431 Pump M1

Y432 Pump M2

X403

X402

X402 Y431

Y432

END

X400 X401

X403

Y430

Y430

Y430

Step Instruction

0 LD X402

1 OR X403

2 AND X400

3 AND X401

4 OUT Y430

5 LD Y430

6 AND X402

7 OUT Y431

8 LD Y430

9 AND X403

10 OUT Y432

11 END

The ladder & IL program for the central heating

system using Siemens PLC is :

Inputs :

I0.0 Clock

I0.1 Boiler sensor

I0.2 Room sensor

I0.3 Tank sensor

Outputs :

Q2.0 Boiler

Q2.1 Pump M1

Q2.2 Pump M2

I0.3

I0.2

I0.2 Q2.1

Q2.2

END

I0.0 I0.1

I0.3

Q2.0

Q2.0

Q2.0

Step Instruction

0 A I0.2

1 O I0.3

2 A I0.0

3 A I0.1

4 = Q2.0

5 A Q2.0

6 A I0.2

7 = Q2.1

8 A Q2.0

9 A I0.3

10 = Q2.2

11 END

Example (Timer Application)

Automatic mixing processes of liquids and other

compounds in the chemical and food industries are very

common.

The mixing station goal is to mix two liquids for a

specified time and then output the final product to a

storage tank.

The system consists of :

1. Two level sensors to monitor the flowing of the

liquids into the tank.

2. Three solenoid valves to control the flow of liquids.

3. A motor connected to an agitator to mix the liquids

into the tank.

Mixing

Station

LS1

LS2

Level Sensors

VA1

VA2

Input ValvesMS

1

Motor & Agitator

Mixing Tank

VA3 Output to Storage Tank

The sequence of events for this automatic mixing process will

be as follows :

1. Open valve 1 until level 1 is reached for the first liquid .

2. Then close valve 1 .

3. Open valve 2 until level 2 is reached for the second

liquid .


5. Start the motor and agitate to mix the liquids into the

tank for a specified time .

6. Then stop the motor .

7. Open valve 3 up to a specified time to empty the mixed

product to a storage tank .


9. Repeat or end the mixing process as required .

The automatic mixing station will require the following

components using Mitsubishi PLC :

1. Inputs to the PLC :

Start push button X400

Stop push button X401

Level sensor LS1

X402

Level sensor LS2

X403

1. Outputs from the PLC :

Valve # 1 (VA1) Y430


Motor starter (MS1) Y432


Q2.2

I0.3

F0.2

F0.1

Q2.0

F0.1

F0.1

F0.1

F0.1

F0.1

I0.0I0.1

F0.1

END

I0.2 I0.3 Q2.2 Q2.3

I0.2 I0.3 Q2.2 Q2.3

Q2.1

F0.2I0.3

Q2.3

F0.3

F0.1 F0.2

F0.1 F0.3 F0.2Q2.3

T0

KT1200

KT180

T1

Counter Application

Consider the following packing machine,

where it is required to pack 6 objects in a

box and then pack 12 objects in another

box in another path as shown :

6 in box

12 in box

Step Instruction

0 LD X400

1 OR C461

2 RST C460

3 K 6

4 LD X401

5 OUT C460

6 LD C460

7 OUT Y430

8 LD X400

9 OR C461

10 RST C461

11 K 12

12 LD X401

13 AND C460

14 OUT C461

15 LD C461

16 OUT Y431

17 END

Mitsubishi PLC program

C460

C461

X400

X401

Y430

RESET

C460

K 6

Out

C460

X400

X401

Y431

RESET

C461

K 12

Out

C461

C461

Exercise

A door system for trains is tested by opening

and closing the doors about 1000 times and on

every fifth closing of the doors, a pneumatic

cylinder out-strokes to simulate an obstruction.

The cylinder will remain in the obstruction

position while the doors attempt to close three

times.

After the third attempt, the cylinder in-strokes

to allow the doors to be fully closed.

Rails

Cylinder

Obstruction

Doors

The door testing system will require the following components

using Mitsubishi PLC :

1. Inputs to the PLC :

Start push button X400

Stop push button X401

Switch to open & close doors X402

Left hand door sensor X403

Right hand door sensor X404

2. Outputs from the PLC :

Left hand door Y430

Right hand door Y431

Cylinder Y432

Filling / Draining Control

Operation

• Charge and discharge of a reservoir is a

common process in industry as well as a need

for mixing two or more substances using

automated valves.

• Consider the charge and discharge system

displayed in figure, it is required to :

a) Operating the process in accordance to

the displayed operating panel.

b) Pressing (T1) on the operating panel, will

open valve (V1) to start filling up with

running the motor (M) until reaching (S1).

c) When completing filling up, valve (V1)

closes, motor stops and valve (V2) opens

to start emptying until reaching (S2) to

close (V2).

d) It is required that the reservoir has to be

filled up and emptied four times with the

same cycle before activating the End-

lamp.

Automation of Parking Garage

• Consider a simple system that can control 100

cars at the maximum.

• Each time a car enters, PLC automatically

adds it to a total sum of other cars found in

the garage.

• Also, each car that comes out will

automatically be taken off.

• When 100 cars park, a notifying signal that the

garage is full will turn on.

• Otherwise a Vacancy signal should turn on.

SEQUENCE CONTROL PROCESS

Consider the motor movement control system

displayed in figure with the following features :

1. When the start button is pressed, the

motor will move from left to right.

2. When LS2 is on, the motor stops, delays for

5 sec. and then moves back to home.

3. When LS1 is on, motor cuts off signifying

that the sequence is completed

Motor Right

Motor Left

LS1 LS2

HOME

StartStop

Product Packaging

Consider the packaging system shown in figure

with the following features :

1. By pushing START key a Flag1 is activated.

2. Resetting depends only on a STOP key).

3. When started, motor of a conveyor for

boxes is activated. The conveyor takes a

box up to the limit switch, and a motor

stops then.

4. Starting the product conveyor is activated

by a limit switch when a box is detected.

5. The presence of a box allows counter to

count 10 products.

6. On activating the conveyor with boxes, a

limit switch resets counter to be ready to

count 10 products again.

7. Operations repeat until STOP key is

pressed.

plc exercises

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