We most often come across light ON OFF control; single switch with multiple conditions using programmable logic control (PLC) is discussed here.
PLC Light ON OFF Control
Note : The above image used only as reference, terminal details may be different with the logic.
Lamp Control Logic
There are only two switch for start and stop lamp. The conditions are,
Note: If stop switch is pressed at any one of the above step, the process should stop.
Inputs and Outputs
PLC Ladder Logic for Light Control
PLC Logic Decription
 RUNG 0000
Latching rung to operate the system through Master Start and Stop switch..Lamp should be turned on when start is pressed.
RUNG 0001 to RUNG 0006
when start is turned on/off memories are latched to store the status of Start switch
RUNG 0007
Conditions are wired in series and parallel to make the condition possible.
Conclusion:
The above explained Light turn ON/OFF control using PLC is for example only. It may vary from real time. We can use this example program to understand the working of memories and Latching in AB PLC.