SCHOOL OF MECHANICAL AND BUILDING SCIENCES

B.Tech Mechanical Engineering - IV semester (FFCS)

Assignment on PLC Programming – May 2010

Course Code : 09MEE229 Course Name : Mechatronics

1. Try to develop the PLC ladder logic program for a relay based controller that will

allow three switches in a room to control a single light.

2. Draw the ladder diagram to represent

(i) Two switches are normally open and both have to be closed for

a motor to operate.

(ii) Either of two, normally open switches have to be closed for a

coil to be energized and operate an actuator?

(iii) A motor is switched on by pressing a spring return bush button

start switch and the motor remains on until another spring return

bush button stop switch is pressed?

3. Develop the ladder logic that will turn on a light, after switch A has been closed 5

times. Push button B will reset the counters.

4. Devise a system, using a PLC that could be used with a conveyor belt which is used to

move an item to work station. The presence of the item at the work station is detected by

means of breaking a contact activated by a beam of light to a photosensor. There it stops

for 100sec for an operation to be carried out and then starts moving. The motor for the

belt is started by a normally open start switch and stopped by a normally closed switch.

5. Devise a circuit that could be used with a domestic washing machine to switch on

pump to pump water for 100 sec into the machine, then switch off the pump and switch

on a heater for 50sec to heat the water. The heater is then switched off and another pump

is switched on for 100sec to empty the water from the machine.

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6. Write a PLC ladder logic program for the following: The figure. 1 illustrates a

conveyor system using two pneumatic cylinders A and B for lowering bales of hay.

Figure. 1. Cylinder Sequential control (B-A+A-B+)

Conveyer 1 supplies bales of hay which need to be lowered to conveyor 2 to be

transported away for storage. The sequencing of the pneumatic spring return cylinders is

critical in order to complete the transfer of each bale successfully.

Note: Both cylinders must never extend together.

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7.. Write the PLC ladder logic program for the electro-pneumatic sequence control

(shown in Figure.2) for the following conditions.

Conditions:

i) Magnetic sensors I1 and I3 are initially sensed.

ii) When the workpiece from conveyor belt 1 reaches to the platform of cylinder

A, then sensor S1 senses it and actuates the cylinder A to extend. This

operation will elevate the workpiece to the conveyer belt 2.

iii) Once the extension is over, Sensor I2 will sense and actuate the cylinder B to

extend this operation and pushes the workpiece to the conveyer belt 2.

iv) After the extension process cylinder A should retract and then the cylinder B

should retract.

v) When the proximity sensor S2 senses the object the conveyer motor2 stops for

5 seconds for machining purpose. After 5 seconds, the conveyor motor2 has to

start again to deliver the machined components to the next machine.

vi) The process should be continuous.

Note : I1, I2,I3 and I4 are the Magnetic sensors placed on the cylinders. S1 and S2 is

the Proximity sensor.

Cylinder A

Cylinder B

Conveyer Belt 1

Conveyer Belt 2S1

I2

I1

I3 I4

Drilling Machine

S2

Workpiece

Figure. 2. Cylinder Sequential control (A+B+A-B-)

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8. Write the PLC program for the following control of a heating oven. application.

The system is started with a Start button that seals in the Auto mode. This can be

stopped if the Stop button is pushed. (Remember: Stop buttons are normally closed.)

When the Auto goes on initially the TON timer is used to sound the horn for the first

10 seconds to warn that the oven will start, and after that the horn stops and the

heating coils start. When the oven is turned off the fan continues to blow for 300s or 5

minutes after.

9. Write the PLC program for the following application.

A counter is used to remove 5 out of every 10 parts from a conveyor with a

pneumatic cylinder. When the part is detected both counters will increase their values

by 1. When the sixth part arrives the first counter will then be done, thereby allowing

the pneumatic cylinder to actuate for any part after the fifth. The second counter will

continue until the eleventh part is detected and then both of the counters will be reset.

10. Write the PLC programming for the following application:

Fig. 1 illustrates a tank of water which is under program control using a PLC.

When the water falls below the float switch level, the tank will be stopped up

automatically by the top-up valve. If the water level remains below the float switch

level for more than 2 minutes, then an audible alarm will sound.

Figure: 1. Water Tank

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