Explain OFF delay timer using example

Application:-Explain OFF delay timer using example. Also draw electrical diagram and PLC program for example

 Components:-Programmable logic controller, Electrical panel, wires, 24VDC switch with NO contacts, 24VDC solenoid valve, and 24 VDC OFF delay timer.

Diagram:-

Explanation:-

Consider one example for OFF delay timer explanation. For example there is a valve in our application and we need to close it after 20sec when switch S1 is pressed. So as shown in above circuit supply will pass from No contact of the switch and will go to timer supply. When switch is pressed timer will start first and operate valve and meanwhile off delay will start so after time valve will be close automatically.

PLC program:-

Write the ladder program for above application using ladder diagram language. Here for ladder logic we can use any supported PLC system like S7-1200, S7-300, S7-1500 or any other PLC which can support this instruction. For PLC logic we need digital inputs and outputs.

For our application start switch S1 is digital input and valve is the digital output. So define digital input address and output address as per below explanation,

Digital inputs:-

Start switch S1=I0.0

Digital Output:-

Valve=Q0.0

PLC program Explanation:-

In network 1 we have taken NO contact of Start switch S1 (I0.0) so when switch is pressed, timer and valve (Q0.0) will start. The set time is 20sec so timer will generate OFF command to stop valve (Q0.0).

Here PT is preset time at which we can set time and ET is elapsed time at which we can monitor time. Do not mix up the pulse timer and OFF delay timer. In pulse timer, timer needs pulse of the digital input for operation and in OFF delay timer, timer needs digital input for operation.