PLC Programming to Control Lights in a Sequence

Develop ladder logic program for a display sign that will sequentially turn ON.

1. Three lights (L1, L2, L3) 3 sec apart.
2. Turn Off all the lights after 6 sec.
3. Three lights (L1, L2, L3) 2 sec apart.
4. Turn Off all the lights after 4 sec
5. Three lights (L1, L2, L3) 1 sec apart.
6. Turn Off all the lights after 2 sec.
7. Repeat the sequence from step 1

PLC Programming Sequence Logic

Program Description:

Rung 0000:

Start/Stop PB latched with memory B3:0/0.

Rung 0001:

B3:0/0 enabled to turn on L1  (O:0/0 ) and Timer  T4:0 to turn on L2.

Rung 0002:

B3:0/0 and T4:0 enabled to turn on L2  (O:0/1 ) and Timer  T4:1 to turn on L3.

Rung 0003:

B3:0/0 and T4:1 enabled to turn on L3 (O:0/1 ) and Timer  T4:2 to turn on L3.

Rung 0004:

B3:0/0 and T4:2 enabled to turn on Timer T4:3 to Set the timers (T4:0, T4:1, T4:2 and T4:3)  preset to 2sec using move block. Comparator blocks which performing equal operation among counter accumulator and timer accumulator value.

Rung 0005:

The counter block is used to count the number of sequences to choose the preset value of timers.

Rung 0006:

B3:0/0 and comparator block enabled to Set the timers (T4:0.T4:1, T4:2 and T4:3)  preset to 1sec using move block. Comparator blocks which performing equal operation among counter accumulator and timer accumulator value.

Rung 0007:

B3:0/0 and comparator block enabled to Set the timers (T4:0.T4:1, T4:2 and T4:3)  preset to 3 sec using move block. Comparator blocks which performing equal operation among counter accumulator and timer accumulator value.

Rung 0008:

B3:0/0 and comparator block enabled are used to reset the counter to repeat the sequence from beginning

Program Output:

When Timers preset value is 3

When Timers preset value is 2

When Timers preset value is 1

Conclusion:

We can use this example to understand the programming logic in Allen Bradley Programmable Logic Controller (PLC).

Author: Hema Sundaresan

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