Quoting Ahti Aintila <[EMAIL PROTECTED]>, on Thu 26 Jun 2008 12:59:31 AM PDT:
> On 26/06/2008, Jim Lux <[EMAIL PROTECTED]> wrote: > >>> The key words when working with relays are debouncing, contact >>> "wetting" currents and contamination control of contact materials. >>> Contrary to the common belief, silver is not the best material for low >>> voltage contacts (<24 V) due to the high breakover voltage of the >>> naturally developing silver oxide and silver sulphide layers. Gold >>> works much better with low voltages and low wetting currents, but is >>> suspectible to mechanical wear. Use vacuum protected read relay >>> contacts whenever applicable. >> >> I hadn't ever thought about it before, but devising a rock solid >> interface to any sort of contacts that someone might hook up to it is >> quite an engineering challenge. Usually, you're designing for some >> small subset, or you actually get to pick the contacts. >> >> I'd guess that you want a fairly decent voltage (12Vish) with a decent >> current (10mA), but your input circuit also needs to tolerate >> transient voltages, etc. >> >> Something like an Optoisolator diode with an optional pullup.... >> (which is what they use on a lot of industrial PLCs). That would give >> you galvanic isolation, too, which is nice. >> >> Jim >> > Jim, > Optoisolator is a good solution, but even those need some kind of > debouncing circuitry, as well as reed relays (sorry for my earlier > mispelling: "read relay"!). Of course... I assume one does most of that in software or programmable logic, as opposed to with the electrical interface. Although.. that 0.1 uF capacitor can do a lot of good.... Jim _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
