jlarkin@highlandsniptechnology.com wrote:> On Fri, 18 Jun 2021 06:38:55 +0100, piglet <erichpwagner@hotmail.com> > wrote: > >> On 18/06/2021 01:46, John Larkin wrote: >>> On Fri, 18 Jun 2021 00:56:55 +0200, Klaus Vestergaard Kragelund >>> <klauskvik@hotmail.com> wrote: >>> >>>> Hi >>>> >>>> I am working on a design where we are monitoring a relay, if it has been >>>> energized. That is done with high ohmic resistor and a source voltage, >>>> detecting a current when drawn >>>> >>>> But, contact wetting could be a problem, so have added a small capacitor >>>> on the contacts, so when they are closed a relatively high current runs >>>> for a short period of time to punch through the oxide layer of the contacts >>>> >>>> I am having difficulty finding any information on the subject, how much >>>> current is needed for punch through and how much time. >>>> >>>> I need a general input, since we do not know if the relay has gold >>>> plated contacts or not >>>> >>>> Anyone got a clue? >>>> >>>> Regards >>>> >>>> Klaus >>> >>> We have a similar issue now. We will sell a general-purpose relay >>> module as part of a modular test system, and we are concerned that >>> once a relay is used to switch power, it may not be good for signals >>> any more. >>> >>> That may be urban legend. It would be awkward to test. >>> >>> >>> >> >> Definitely not an urban legend. I have read a warning about gold plated >> contacts in some manufacturer's datasheet, possibly Tyco? >> >> piglet > > Got a link to a data sheet or appnote? It would be nice to find a > general-purpose relay contact material. Maybe not down to > thermocouples, but amps to mA maybe. > > >ISTR that somebody makes gold-over-rhodium contacts, so that they're good for dry circuits as well as power. Of course as you say, once you blow the gold off it's not a dry-contact relay anymore. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Wetting current
Started by ●June 17, 2021
Reply by ●June 18, 20212021-06-18
Reply by ●June 18, 20212021-06-18
Pickering make a wide range of reed relays and provide a lot of advice on how to choose and use them. www.pickeringrelay.com John
Reply by ●June 18, 20212021-06-18
On Fri, 18 Jun 2021 09:18:19 -0700 (PDT), John Walliker <jrwalliker@gmail.com> wrote:>Pickering make a wide range of reed relays and provide a lot of advice on how to choose and use them. > >www.pickeringrelay.com > >JohnThey made an RTD simulator with a heap of reed relays and resistors. It was a horror. We do it electronically, which avoids all sorts of interesting effects.
Reply by ●June 18, 20212021-06-18
On 6/18/2021 3:46, John Larkin wrote:> On Fri, 18 Jun 2021 00:56:55 +0200, Klaus Vestergaard Kragelund > <klauskvik@hotmail.com> wrote: > >> Hi >> >> I am working on a design where we are monitoring a relay, if it has been >> energized. That is done with high ohmic resistor and a source voltage, >> detecting a current when drawn >> >> But, contact wetting could be a problem, so have added a small capacitor >> on the contacts, so when they are closed a relatively high current runs >> for a short period of time to punch through the oxide layer of the contacts >> >> I am having difficulty finding any information on the subject, how much >> current is needed for punch through and how much time. >> >> I need a general input, since we do not know if the relay has gold >> plated contacts or not >> >> Anyone got a clue? >> >> Regards >> >> Klaus > > We have a similar issue now. We will sell a general-purpose relay > module as part of a modular test system, and we are concerned that > once a relay is used to switch power, it may not be good for signals > any more. > > That may be urban legend. It would be awkward to test. > > >My experience is not very extensive but does cover things close to both extremes you seem to be looking at. In the netMCA-3 signals (gain, switches opamp stages/feedbacks, fairly wideband so the currents are not unthinkably low) get switched by latching DPDT relays (no longer in production and alas, our stocks are getting low - replaceable but no drop-in) and these work for years without causing any issues at 14 bit overall precision. At the other extreme I have relays switching on/off ventilator heaters here so they maintain a constant temp. About 2kW each, 220V AC. The relays last for 1-2 winters and then begin to stays stuck, not too badly welded as a kick to the housing unwelds them for some time (usually has to be done during the night when you wake up and notice it...). I'd definitely not trust these relays for signal switching even after a very short use with the ovens. (Obviously the relay types are quite different, the power ones have been different over time, same behaviour though). Dimiter ====================================================== Dimiter Popoff, TGI http://www.tgi-sci.com ====================================================== http://www.flickr.com/photos/didi_tgi/
Reply by ●June 18, 20212021-06-18
John Larkin <jlarkin@highland_atwork_technology.com> wrote:> On Fri, 18 Jun 2021 09:18:19 -0700 (PDT), John Walliker > <jrwalliker@gmail.com> wrote: > >>Pickering make a wide range of reed relays and provide a lot of advice on how to choose and use them. >> >>www.pickeringrelay.com >> >>John > > They made an RTD simulator with a heap of reed relays and resistors. > It was a horror. We do it electronically, which avoids all sorts of > interesting effects.What's some weirdness you see with reed relay logic?
Reply by ●June 18, 20212021-06-18
On 18/06/2021 15:31, jlarkin@highlandsniptechnology.com wrote:> > Got a link to a data sheet or appnote? It would be nice to find a > general-purpose relay contact material. Maybe not down to > thermocouples, but amps to mA maybe. > > >I think I saw it SDS Relais-now Panasonic or Omron but am away from my bookshelf. I think it is also in AoE X-chapters. See page 4 of this from Phoenix Contact: <https://www.phoenixcontact.com/assets/downloads_ed/global/web_dwl_technical_info/105396_en_00.pdf> piglet
Reply by ●June 18, 20212021-06-18
On 17/06/2021 23:56, Klaus Vestergaard Kragelund wrote:> Hi > > I am working on a design where we are monitoring a relay, if it has been > energized. That is done with high ohmic resistor and a source voltage, > detecting a current when drawn > > But, contact wetting could be a problem, so have added a small capacitor > on the contacts, so when they are closed a relatively high current runs > for a short period of time to punch through the oxide layer of the contacts > > I am having difficulty finding any information on the subject, how much > current is needed for punch through and how much time. > > I need a general input, since we do not know if the relay has gold > plated contacts or not > > Anyone got a clue? > > Regards > > KlausThis Axicom databook looks helpful on different contact material properties (circa pages 13-20): <http://www.farnell.com/datasheets/105262.pdf> piglet
Reply by ●June 18, 20212021-06-18
On Fri, 18 Jun 2021 19:08:37 +0000 (UTC), Cydrome Leader <presence@MUNGEpanix.com> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> wrote: >> On Fri, 18 Jun 2021 09:18:19 -0700 (PDT), John Walliker >> <jrwalliker@gmail.com> wrote: >> >>>Pickering make a wide range of reed relays and provide a lot of advice on how to choose and use them. >>> >>>www.pickeringrelay.com >>> >>>John >> >> They made an RTD simulator with a heap of reed relays and resistors. >> It was a horror. We do it electronically, which avoids all sorts of >> interesting effects. > >What's some weirdness you see with reed relay logic?In the RTD case, horrible transient values when a value is changed. like spiking to 500 deg C for some milliseconds, going from 48 to 49. Engine control computers don't like that. Reeds have huge thermoelectrics too. Lots of intermetallic splices with a heater roughly in the middle. I discovered reed twang some years ago. The reed wiggles like a struck bell when it's energized, very complex waveforms lasting many milliseconds. In the coil mag field, that makes biggish voltages.
Reply by ●June 18, 20212021-06-18
John Larkin wrote:> > We have a similar issue now. We will sell a general-purpose relay > module as part of a modular test system, and we are concerned that > once a relay is used to switch power, it may not be good for signals > any more.Just make them all the same and spec them differently, with different markings on the terminals. You could even make a whole assortment of models, with half the channels spec'd for power, or 25% or 10%. -- Defund the Thought Police
Reply by ●June 19, 20212021-06-19
On 18/06/2021 07.38, piglet wrote:> On 18/06/2021 01:46, John Larkin wrote: >> On Fri, 18 Jun 2021 00:56:55 +0200, Klaus Vestergaard Kragelund >> <klauskvik@hotmail.com> wrote: >> >>> Hi >>> >>> I am working on a design where we are monitoring a relay, if it has been >>> energized. That is done with high ohmic resistor and a source voltage, >>> detecting a current when drawn >>> >>> But, contact wetting could be a problem, so have added a small capacitor >>> on the contacts, so when they are closed a relatively high current runs >>> for a short period of time to punch through the oxide layer of the >>> contacts >>> >>> I am having difficulty finding any information on the subject, how much >>> current is needed for punch through and how much time. >>> >>> I need a general input, since we do not know if the relay has gold >>> plated contacts or not >>> >>> Anyone got a clue? >>> >>> Regards >>> >>> Klaus >> >> We have a similar issue now. We will sell a general-purpose relay >> module as part of a modular test system, and we are concerned that >> once a relay is used to switch power, it may not be good for signals >> any more. >> >> That may be urban legend. It would be awkward to test. >> >> >> > > Definitely not an urban legend. I have read a warning about gold plated > contacts in some manufacturer's datasheet, possibly Tyco? > > pigletI seen many examples listed, but no real accurate numbers
