PLC turn-off delay Tdoff ladder diagram instruction

Referring to the timer delay related instructions in the PLC ladder diagram instructions, we are now discussing about another timer delay called turn-off delay (Tdoff). 

Turn-off delay instruction symbol

When ever the input to this instruction changes from false to true, it will output true for a specific delay time. The input high time must greater or equal to the PLC cycle time.

Timing diagram for Turn-off delay instruction

Let see a very simple example. I use an input contact to turn on an output coil for 10 seconds.

Turn-off delay ladder diagram instruction example

We configure the Tdoff instruction as below.

The delay time is set to 10000 mS or 10 second.

It's convenience to add a one-shot rising to the rung to prevent the rung become true while the input contact X0 is in a long press duration.

The remanding open-circuit rungs are just an example of cutting the rungs. 

For a serious PLC programmer they always need to test the program in both hardware and software. However, we already know that the overall program is completedly work. So It's not necessary to test this program in another software simulation and in the hardware.

Schematic diagram

Click here to download the zip file of this ladder diagram example.