Establishing & managing redundancy of Potential Free contacts


Thread Starter


I am looking to establish redundancy amongst potential free contacts. For this application, i require two Potential free contacts to be used as redundant inputs giving a single Changever contact output. I understand, these pot. free contacts can be taken as DI into some PLC and managed there, by means of DO using some logic configured in PLC, but i want to avoid that route.. Plz Help!
potential free contacts

Contacts can be potential free in a standalone device, but for any means of control some voltage/current has to be present in order to sense the presence or absence of the voltage/current. So some voltage has to be applied to your 'sensor' contacts. 24Vdc is generally used in industrial apps. 24Vdc power supplies are available anywhere in the world.

>DO using some logic configured in PLC; I want to avoid that route

Well, that leaves relay logic. You need a SPST N.O. 24Vdc relay. And, if it's a plug-in relay, the socket it plugs into.

>redundant inputs giving a single Changever contact output.

Redundant means more than one, so you need two of your (whatever they are) sensor devices

Wire +24Vdc (from the power supply) to one of the contacts on each of your redundant devices.

Wire the remaining contact on your devices to one terminal of the coil of the relay.

Wire the other side of the relay's coil to the negative or return of the 24Vdc power supply.

What you get is a circuit that will close the relay's contacts when either or both of the sensor devices close their contacts.

It does not use a PLC and it has 'redundant' sensors.

Timothy Niemczyk

Take a look at Sprecher CS1 Relay as a possible solution. All contacts are double breaking and sealed against dust and foreign matter. Blank contact elements are also available for filling unused spaces within
the relay (required). Pretech Solutions Inc. uses an Output Diagnostic Module that can monitor the control loop for Open, Short and Power Loss as well as indicating if the relay is energized or de-energized.