Quote Originally Posted by Clive S View Post
This is it http://uk.rs-online.com/web/p/signal...oning/4184859/

I think they are used in industry to remote measure sensors etc over a two wire system like this;-

https://www.acromag.com/sites/defaul..._Loop_904A.pdf

http://www.murata-ps.com/data/meters/dms-an20.pdf
Thanks Clive, I had found it on RS but it still didn't mean a lot!! I have bought a second hand cabinet and it came with a few bits and bobs left inside there were a couple of these which I did not recognise- don't think they will be all that useful! eBay...