Quench system

Usually, when a SCADA senses a temperature highier than the set, the PLC sends a signal to energies a relay that opens the valve and switches on the pump at the same time. I am currently facing a problem of the PLC failing to energise the relay. What could be the problem?

Colin.

The PLC output, the relay coil or the relay contacts are not OK.

Many possibilities.

The PLC could have stopped.

There could be no power to the output circuit.

The PLC output could be bad.

The temperature signal into the PLC could have failed.

There may be other conditions in the logic controllinig the output that are not met.

The relay itself could have failed.

The quickest way to check whether the problem is in the PLC or external to it is to look at the LED on the PLC output module corresponding to the relay. If the LED is on but the relay is not energizing, the problem is external to the PLC.

If the LED is not on, there is a good chance the PLC is not commanding the relay to be energized. I can't say for sure because you have not identified the PLC. On some PLC brands the LEDs on output modules are powered from the load side, so the PLC logic may be trying to turn on the output but if there is no power to the circuit the LED can't turn on.

Oh guys thanks for the responses. The PLC is ls-xgb type and its used to control so many other circuitrys which are functioning well. its only this output that is not energising. Please look into that.

Please look into that

Click to expand...

Sorry, but you are the person who will have to do the "looking into".

Nobody here has a copy of the program running on your PLC. Nobody here is in a position to to check your system. The best we can do is offer you suggestions about where to look and what to check.

THANKS AGAIN.

I am looking into everything listed. I will be back with my findings.