On Wed, 30 Jun 2021 15:16:26 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Wednesday, June 30, 2021 at 1:40:53 PM UTC-7, John Larkin wrote: >> On Wed, 30 Jun 2021 11:30:46 -0700 (PDT), whit3rd <whi...@gmail.com> >> wrote: >> >On Saturday, June 19, 2021 at 6:26:16 PM UTC-7, John Larkin wrote: > >> >Reeds have their uses. >> >I'm puzzled how there's a thermocouple problem; other than length of the capsule, >> >there's nothing to encourage thermal gradients, and both glass-seal metal elements >> >ARE the same alloy. Contact plating is a few microns, not a problem at all. > >> Nice in theory, but they have terrible thermocouple offsets in real >> life. The coil gets hot and the leads are not the same metal as the >> reeds. > >The leads are part of the magnetic circuit, they ARE the same metal in >all the examples I've seen. Are you talking about RELAY leads, or reed leads?In a reed relay, the tangs that come out of the capsule are welded od soldered to the copper pins that solder to the PCB. That make two thermocouple junctions. There is stress relief involved, because stress on the reeds can make the relay malfunction. Really, get a reed relay, connect it to a good DVM, apply coil power, and watch.> >Coil dissipation is less of an issue in latching relays, but you can make those with reeds >if you care to. It's an easy design with a cruciform pole piece.We use latching versions of the Fujitsus for microvolt stuff. They cost a bit more. DPDT is often handy.
Wetting current
Started by ●June 17, 2021
Reply by ●June 30, 20212021-06-30
Reply by ●July 1, 20212021-07-01
On Thursday, July 1, 2021 at 6:52:26 AM UTC+10, John Larkin wrote:> On Wed, 30 Jun 2021 11:00:01 -0700 (PDT), whit3rd <whi...@gmail.com> > wrote: > >On Friday, June 18, 2021 at 2:11:47 PM UTC-7, John Larkin wrote: > >> On Fri, 18 Jun 2021 19:08:37 +0000 (UTC), Cydrome Leader > >> <pres...@MUNGEpanix.com> wrote: > > > >> >What's some weirdness you see with reed relay logic? > > > >>... 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. > > > >That's why one 'powers' a relay coil, instead of signalling it. > >The motion of the contacts means the device is an electric motor, > >with all the back-EMF you expect, generated by moving > >magnetic parts in the field of the coil. > > Why do some people love and defend reeds? They are expensive, > unreliable, usually just SPST, twang, have big thermals, are giant > compared to a modern telecom relay, and have to be kept apart from one > another.But they do have unique properties which are sometimes useful. Nobody sane expects to use the same part for every job, and anybody sensible keeps track of stuff that can be bought off-the shelf to deal with specialised problems.> You and Sloman love reeds and love China. You're probably the same person.We don't "love" reeds, or China. We just object to dim-wits like you posting your fatuous misapprehensions about them and pretending you know what you are talking about. I'm pretty confident that I haven't posted anything that ended up as being shown as coming from whit3rd at gmail.com. John Larkin doesn't seem to know how these things work. -- Bill Sloman, Sydney
Reply by ●July 2, 20212021-07-02
Joe Gwinn <joegwinn@comcast.net> wrote in news:3mpncgleb1jbu73395lgi9cgrl8ucte2ja@4ax.com:> 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? > > There are books written on electrical contacts and their design > for various conditions. Unless the current is very small gold > tends to weld. Rhodium is better in such cases. > > Joe Gwinn >I thought that the best contact surface/media was platinum.
Reply by ●July 2, 20212021-07-02
John Larkin <jlarkin@highland_atwork_technology.com> wrote in news:fqqncg50hpi43anlhmglts2db61n3gh8is@4ax.com: snip> 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.High freq relays with SMA I/O ports are supposed to address small signal long term reliability. A GP relay would if the right contact media is used and if it is environmentally sealed. Then each physical connection node needs to be gas tight as well Use an anti-oxidant paste like the cable TV guys use on outside F-fittings. Air exposed contacts can build a film if the atmosphere they are in. The old reed switch operated pinball machines were a joy to work on because the contacts had to be 'burnished' individually because they used the cheap contact materials back then that would rub off if you cleaned them wrong. A poor reed switch was always the first thing one would search for when working on a faulty machine (that contained several dozen). And they switched higher currents and voltages then than today's modern pinballs, so the contacts could go bad pretty quickly. Especially since their closure usually involved the firing of a solenoid making for back EMF current and arcs at the contacts, etc.
Reply by ●July 2, 20212021-07-02
Piglet <erichpwagner@hotmail.com> wrote in news:saisfb$e1g$1@dont-email.me:> On 17/06/2021 23:56, Klaus Vestergaard Kragelund wrote: >> Hi >> >> I am working on a design where we are monitoring a relay, if it >> has been energized. That is done with high ohmic resistor and a >> source voltage, detecting a current when drawn >> >> But, contact wetting could be a problem, so have added a small >> capacitor on the contacts, so when they are closed a relatively >> high current runs for a short period of time to punch through the >> oxide layer of the contacts >> >> I am having difficulty finding any information on the subject, >> how much current is needed for punch through and how much time. >> >> I need a general input, since we do not know if the relay has >> gold plated contacts or not >> >> Anyone got a clue? >> >> Regards >> >> Klaus > > This Axicom databook looks helpful on different contact material > properties (circa pages 13-20): > > <http://www.farnell.com/datasheets/105262.pdf> > > piglet >Hahahaha... A quote... ENG (gas-tight plastic sealed relays filled with insulting inert gases) They have to be sealed to keep the insults inside.
Reply by ●July 2, 20212021-07-02
Piglet <erichpwagner@hotmail.com> wrote in news:saisfb$e1g$1@dont-email.me:> 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 >> >> Klaus > > This Axicom databook looks helpful on different contact material > properties (circa pages 13-20): > > <http://www.farnell.com/datasheets/105262.pdf> > > piglet >Very nice. Page 11 up until they start going over their actual products is very informative about contact science.
Reply by ●July 2, 20212021-07-02
Clifford Heath <no.spam@please.net> wrote in news:168b11ac909b0362$1$2193376$28dd226e@news.thecubenet.com:> On 23/6/21 8:32 am, Cydrome Leader wrote: >> Bill Sloman <bill.sloman@ieee.org> wrote: >>> On Sunday, June 20, 2021 at 11:26:16 AM UTC+10, John Larkin >>> wrote: >>>> On Sat, 19 Jun 2021 21:21:56 +0000 (UTC), Cydrome Leader >>>> <pres...@MUNGEpanix.com> wrote: >>>> >>>>> John Larkin <jlarkin@highland_atwork_technology.com> wrote: >>>>>> On Fri, 18 Jun 2021 19:08:37 +0000 (UTC), Cydrome Leader >>>>>> <pres...@MUNGEpanix.com> wrote: >>>>>> >>>>>>> John Larkin <jlarkin@highland_atwork_technology.com> wrote: >>>>>>>> On Fri, 18 Jun 2021 09:18:19 -0700 (PDT), John Walliker >>>>>>>> <jrwal...@gmail.com> wrote: >>> >>> <>snip> >>> >>>>> maybe you need some lovely mercury wetted relays. >>> >>> They are nice but you do have to mount them so they stray >>> vertical. Orientation-insensitive mercury wetted reeds did get >>> touted from time to time, but never lasted. >>> >>>> We use lots of Fujitsu FTR-B3G relays... almost 100K so far. >>>> >>>> DPDT, surface mount, small and reliable. We use the latching >>>> version at thermocouple levels. They are good up to 3 GHz too. >>>> >>>> Reeds are expensive junk. >>> >>> Of course Bell Labs develped them because they needed something >>> more reliable than traditional relays for the telephone network. >>> >>> They were invented in Russia in 1922, but Bell Labs developed >>> them into something useful in the 1930s - there's a 1941 US >>> patent. >>> >>> If John Larkin doesn't like them, it probably means that he >>> didn't use them as carefully as he should have. >>> >>> https://en.wikipedia.org/wiki/Reed_switch >> >> Well it's not 1930 anymore and the applications for reed switches >> are few and far in between. The wiki article even mentioned reed >> switches being used as sensors in old brushless motors. Awful. > > Bosch are still using reed switches to make their dishwashers > unreliable > > So much for "German engineering" > > CH >Pretty goddamned good piece of gear anyway.
Reply by ●July 2, 20212021-07-02
On 2/7/21 3:33 pm, DecadentLinuxUserNumeroUno@decadence.org wrote:> Clifford Heath <no.spam@please.net> wrote in > news:168b11ac909b0362$1$2193376$28dd226e@news.thecubenet.com: >>> Well it's not 1930 anymore and the applications for reed switches >>> are few and far in between. The wiki article even mentioned reed >>> switches being used as sensors in old brushless motors. Awful. >> >> Bosch are still using reed switches to make their dishwashers >> unreliable >> >> So much for "German engineering" >> >> CH >> > > Pretty goddamned good piece of gear anyway.50% rate of intermittent or total failure in a $1600 appliance because of a badly installed $0.01 part does not constitute a "goddamned good piece of gear".
Reply by ●July 2, 20212021-07-02
DecadentLinuxUserNumeroUno@decadence.org wrote:> Piglet <erichpwagner@hotmail.com> wrote in > news:saisfb$e1g$1@dont-email.me: > >> 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 >>> >>> Klaus >> >> This Axicom databook looks helpful on different contact material >> properties (circa pages 13-20): >> >> <http://www.farnell.com/datasheets/105262.pdf> >> >> piglet >> > > Hahahaha... A quote... > > ENG (gas-tight plastic sealed relays filled with insulting > inert gases) > > > They have to be sealed to keep the insults inside. >We live in 'opes. ;) Cheers Phil Hobbs
Reply by ●July 2, 20212021-07-02
On Friday, 2 July 2021 at 05:58:09 UTC+1, DecadentLinux...@decadence.org wrote:> The old reed switch operated pinball machines were a joy to work on > because the contacts had to be 'burnished' individually because they > used the cheap contact materials back then that would rub off if you > cleaned them wrong. A poor reed switch was always the first thing > one would search for when working on a faulty machine (that contained > several dozen). And they switched higher currents and voltages then > than today's modern pinballs, so the contacts could go bad pretty > quickly. Especially since their closure usually involved the firing > of a solenoid making for back EMF current and arcs at the contacts, > etc.I thought that reed switch contacts were always sealed in a glass tube, so how were these pinball machine reed switches constructed? John
