PLC Ladder Logic Lab

PLC Basic Course on Ladder Logic Diagrams Programming

Exercise 1: Combination Circuits using Contacts/Switches and Relays/Coils

1.1. The door bell y0 is only rung when the door switch push button x0 is pressed

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1.2. Define OR Gate function with the help of ladder.

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1.3. Define NOR Gate function with the help of ladder

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1.4. Define AND Gate function with the help of ladder

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1.5. Define NAND Gate function with the help of ladder

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1.6. Define XOR Gate function with the help of ladder

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1.7. Multiplexer Circuit. Use the truth table below

x0 x1 y0 y1 y2 y3

0 0 0 0 0 1

0 1 0 0 1 0

1 0 0 1 0 0

1 1 1 0 0 0

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Problems:

Problem 1-A. Design circuit to control start/Stop operation of a Fan. (Use two push buttons X0, X1

for start stop operations)

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Problem 1-B. Solve (Problem 1-A).Design a circuit to control start/Stop operation of a Fan. (Use two

push buttons X0, X1 for start stop operations) using Hold condition of Push Button

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Problem 1-C. Solve (Problem 1-A).Design a circuit to control start/Stop operation of a Fan. (Use two

push buttons X0, X1 for start stop operations) using Hold condition of Push Button by Internal retentive

coil of PLC

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Problem 1-D. Solve (Problem 1-A).Design a circuit to control start/Stop operation of a Fan. (Use two

push buttons X0, X1 for start stop operations) using Hold condition of Push Button by Set And Reset

Instruction of PLC.

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Problem 1-E. Solve (Problem 1-A).Design a circuit to control start/Stop operation of a Fan. (Use two

push buttons X0, X1 for start stop operations) using only one pushes Button.

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Problem 1-F. Solve (Problem 1-A).Design a circuit to control start/Stop operation of a Fan. (Use two

push buttons X0, X1 for start stop operations) using only one push Button by toggle instruction.

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Exercise 2:

Timers

2.1. Timers CV accumulate counting after PV is met, when no stop contact is added.

2.2. Timer reset to its original value and starts counting again when stop contact of the

same timer is added.

2.3. Timer CV stops counting using built in function M1957.

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PROBLEMS

Problem 2-A. Output y0 is "ON" After 20 Seconds when Push Button X0 is pushed.

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Problem 2-B Output y0 is flickered by using two timers, when push Button X0 is pushed. (Use

5 second interval between ON/OFF)

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Problem 2-C X0 and X1 are two push buttons. When X1 is pushed Lamp "L1" and "L2" will go

"ON" after 10 seconds "L1" will be "OFF" and "L3" "ON". Whereas "L2" remains

"ON". Whole Circuit is stopped by Pushing "X0".

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Problem 2-D Motor control circuits

There are three push buttons X0, X1, X2. When X1 is pushed motor Starts rotating Clock wise. When

push Button X2 is pushed it rotates CCW while it stops Rotating by pushing X0.

(a) Design the ladder logic assuming there is no delay in changing the direction of motor

(b) Design the ladder logic Assuming 10 second delay in changing the direction of motor

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Problem 2-E Traffic Signals Ladder logic. Push Button X0 is used to start the signals. Green signal is

"ON" for 30 seconds then yellow for 10 seconds then red for 30 seconds then

yellow for 10 seconds and it repeats.

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COUNTERS

Exercise 3:

Problem 3-A. When push button X1 is pressed 10 times then Led1 is "ON". It is "OFF" by X0.

Note: Problem with push button: It creates noise due to mechanical contacts. Solution: function

of plc difu and upper/down edge contact input

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Problem 3-B. Solve problem 3-A above using upper/down edge contact or Difu

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Problem 3-C. Counting Boxes: Boxes move continue on conveyor belt one by one. And one counter

counts boxes, when counter count 10 boxes then conveyor belt will be stopped

and alarm “ON”. After 1 minute alarm will be stopped and conveyor belt will be shut

down.

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Problem 3-D. Automatic count boxes (use M1922). When counter counts 10 boxes then conveyor stop

and alarm "ON" and after "1" minute Alarm "FF"

NOTE: M1922 gives a pulse clock of 1 second

Other Instructions:

MOV

INC

Shift right

Shift left

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Compare

Addition/Subtraction

Label

Jump

For

next

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This control system will work fine, so long as no one pushes both buttons at the same time. If someone were to do that, phases A and B would be short-circuited together by virtue of the fact that contactor M1 sends phases A and B straight to the motor and contactor M2 reverses them; phase A would be shorted to phase B and vice-versa. Obviously, this is a bad control system design! To prevent this occurrence from happening, we can design the circuit so that the energization of one contactor prevents the energization of the other. This is called

Interlocking and it is accomplished through the use of auxiliary contacts on each contactor, as such:

Now to add hold condition of push buttons and momentarily stop button

Now to add Delay Between the Change of Direction of Motor to accommodate the inertia forces.

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Problem 3-C:

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PLC Ladder Logic Lab