Hard-wired 2oo3 Relay Logic 1

[nhcf]

I am looking to implement 2oo3 relay logic to shutdown process equipment. It will tie into an existing hard-wired master control circuit that is normally energized, de-energize to trip.

Three output channels from an existing PLC, through interposing relays that are hardwired in 2oo3 configuration will be connected into the existing master control relay coil circuit.
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Is there a manufacturer who makes pre-configured plug-in relay modules with 2oo3 logic already configured?

 

[sunnysky]

A-B,... other companies offering these are Banner, Schmersal, Pilz, Norstadt, STI. You can't just use any "highly reliable" relay, the relay also must have guided contacts. This means that on a 4-pole NO & NC relay, if any one NO contact welds, then none of the 4 NC contacts will be allowed to make when the coil is de-energized.

 

[nhcf]

It sounds like you are talking about using three single relays, wired in 2oo3 configuration. I was questioning if there was a pre-configured module or board, three plug-ins, 3 coils, and outputs already factory-configured for 2 oo3 logic. I don't think there is, that i have found.

 

[sunnysky]

I doubt it as well. In fact I'd never heard of 2oo3 before this question. It reminds me of an aerospace project I did in the 70's with 96 hogh power relays in a box controlled by custom SCADA solution I designed for pre-launch used to charge batteries etc. I ordered sense contacts on each relay and checked by remote after every toggle command. During my R&D tests the relays were found to be flakely. Then I discovered the facts about 10% wetting current and used an RC capacitor discharge to make the contacts relaible to signal TTL logic levels.


My way of thinking about MTBF is not just 2oo3 but make 1 better by not degrading the MTBF from 10^7 mechanical contacts to 10^3 from over stress and improper derating or insufficient arc suppression but I don't know the application. Elevator? Aerosapce?