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; in other words, after the push button is pressed, the output is turned on to remain energized (ON) even when the button is released.

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

A latch and unlatch program using normally open push buttons for both starting and stopping

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

Figure 9.27 – A latch and unlatch program using normally open push buttons for both starting and stopping

The PLC wiring for the program is as follows:

Figure 9.28 – Wiring to implement a latch and unlatch program using normally open...