wthomas (Customer) asked a question.
Low voltage load switching on relays
I have an external component with dry contacts that I need to close to trigger events. There are 8 contacts that share 1 common. I was planning on using P1-16TR to close the contacts to trigger events but a voltmeter on the dry contacts show 3V. I believe the P1-16TR is rated for a switching voltage of 6-30VDC. Will it truly not switch 3V? How might I switch these low voltage loads.
When new and clean it almost certainly will switch 3V, the problem might come with age. Relay contacts can oxidize and/or become contaminated and that can cause problem with very small signals, higher voltages (and currents) can "burn" off the contamination which is a reason for minimum ratings.
There are relays made for small signals, generally with gold plated contacts (or, rarely, mercury wetted). for example them specs for the Fuji Electric RS4N-D that AD sells says:
Contact Material Silver alloy (gold-plated)
Min. Operating Voltage and Current 0.1 VDC, 1mA
A possible option would be to run 24V thru the P1-16TR and let that power RS4N-DE (or equivalent) relays that in turn switch your small signal. That will cost some money and wiring, but it is an option.
Another option is to just use the P1-16TR as is and hope for the best, chances are good it will work OK. In the last 20 or so years I have replaced a handful of general purpose relays that failed switching tiny loads, but that is a handful in 20+ years, how critical is your application?
I like it when people read the spec sheets! :)
kudos
My previous comment is pointed at whoever designed a machine that I am compelled to support!
The machine was designed around a 784-4C-24D relay (or equivalent) matrix of +50 relays to connect/disconnect DUTs to an Agilent LCR meter.
The relay spec sheet shows : Minimum Switching Requirement 10mA @ 17VDC
The meter delivers less than 1VDC to the DUT.
Spec sheets are wonderful things.
Thanks Tinker, I appreciate your helpful response.
It's a residential install with an estimated 1000 switches per year in a relatively clean environment for a non-critical application. While I'd probably be safe to switch in the P1-16TR for my use case, I'll look into relays made for small signals and trigger it with an output device like P1-15TD2. If I end up using the P1-16TR, I'll make sure to document that I'm intentionally taking risk and using beyond the minimum rating. That way other people servicing this down the road will I understand my intent and know I read the spec sheet :)