Latching and unlatching in PLC programming

Latching is a technique used to keep an output energized or activated even when the input ceases. Latching makes a momentary push button act as a maintained switch i.e. after the push button is pressed, the output it turned on remain energized (ON) even when the button is released.

Unlatching is simply a method or technique used to de-energize a latched output.

Latch and unlatch program using normally open push buttons for both start and stop

Write the simple program in network 3 to see how latching and unlatching works with normally open push button for start and normally open push button for stop:

Figure 9.27 – Latch and unlatch program using normally open push buttons for both start and stop

The PLC wiring for the program is as follows:

Figure 9.28 – Wiring to implement latch & unlatch program with normally open push buttons used for both start and stop

The preceding wiring diagram in shows the start push button (normally...