Excessive Current damaging the components of the circuit.

Diver300 said:

What is the power supply? If the voltage is too large or there is too much ripple, the power supply circuit of the second pressure transducer could be taking more current.

Can you tell us the make and model of the pressure transducer?

It might be better to arrange to have two relays, one powered from each pressure transducer, so that you aren't turning the second transducer on and off.

Your first post mentioned the failure of the first pressure switch. You've now said that it has an error condition, not a failure. I think that you would have had an answer sooner if you had given out more information sooner.

Click to expand...

mpapreja said:

here i have attached the main circuit of the pressure switch and the error we are getting at the time of failure .

please check if this can be helpful

Click to expand...

Tony Stewart said:

There is a need to make measurements for R, L but I have made certain assumptions from datasheets I found and show a functional circuit. However, if the internal clamp diode in this model latching relay was blown open, the PNP switch inside the Pressure switch would fail from over negative voltage. HV crosstalk from opening the latching relay current will also be a problem , so a reverse 1A clamp diode needs to go across the relay contacts e.g. 1N400x Keeping all inductive wire pairs twisted (+/-) helps reduce crosstalk .

Conclusion. The only problem I see without more measurement details and photo is the lack of flyback diode clamp for the solenoid. Since it is a latching relay the duration on the relay can be short, but the inductive current switched off from the estimated < 5A solenoid will be many xx kV and arc the contacts and weld them shorted from corona.

Ensure reverse voltage clamp diode across switch. The slow down of armature will not be a problem if this a latching relay if my understanding is correct.

Click to expand...

rjenkinsgb said:

Is there a flywheel diode connected across or built in to the solenoid coil?

If not, the back EMF from that could be spiking the pressure switches.

Click to expand...

Diver300 said:

It would be really useful if you could read the current with an oscilloscope as the pressure switches are turning on and off.

However, that might be difficult, and devices like that pressure switch are really not designed to be turned on and off with similar devices.

I suggest that you reverse the direction of operation of the relay, and the pressure switches, and connect the two pressure switches so that they are permanently powered and so that either can operate the relay.

As far as I can see from the instructions of the pressure switches, you can change their operation from normally open to normally closed by lots of button presses from the front panel. The relay can be changed by swapping the wires on 2 and 4, and moving the wire from 5 to 7. You should connect the 24 V power to the brown wire on both pressure switches, and both black wires to the connection 8 on the relay.

The logic should be the same. Instead of operating the solenoid when both switches operate, you are turning off the solenoid when either switch doesn't operate, which comes to the same thing.

It would also be possible to add another relay, but I would not be turning the pressure switches on and off.

Click to expand...