Develop ladder logic program for a display sign that will sequentially turn ON.
- Three lights (L1, L2, L3) 3 sec apart.
- Turn Off all the lights after 6 sec.
- Three lights (L1, L2, L3) 2 sec apart.
- Turn Off all the lights after 4 sec
- Three lights (L1, L2, L3) 1 sec apart.
- Turn Off all the lights after 2 sec.
- 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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