Been looking into sealing current for some contacts.
With little to go on, I'm swagging 20mA for a goal.
But I'm curious why a cap might not also be part of the answer. My thinking is inrush current would do as well as continuous current in cleaning things up. But find little if anything on the problem, and nothing on using caps.
Comments?
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Mercury-wetted reed switches work even better, though you do have to mount them within 15 degrees of the vertical.
Contact resistance is a bit less than you get with noble-metal tipped reeds, you get ten times the operating life-time, and the contact resistance is quite a lot more stable from one contact episode to the next.
Thermocouple voltages are always a problem with reed switches - it's hard to get them down to microvolt levels.
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(and, unfortunately, tested for 911 multiple times in the past few years... without a hitch). ...Jim Thompson
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It's what you learn, after you know it all, that counts.
eeds, you get ten times the operating life-time, and the contact resistance is quite a lot more stable from one contact episode to the next.
rd to get them down to microvolt levels.
And you didn't bother to point out that mercury-wette4d reeds don't bounce.
That's a bit silly. If you think contact bounce in reed switches is importa nt enough to make a fuss about (and I never found it to present enough of a problem that I had to do something about it) you might at least have taken the time to mention that mercury-wetted reeds don't bounce.
Worse than bounce is twang. After the contacts finally close, the reeds still vibrate in the mag field of the coil, and generate a complex waveform that looks, on a scope, much like the sound of a bell ringing. It can mess up low-level measurement for many milliseconds. Well, if you dare to use reeds for low-level measurement.
Reeds are horrible. You get a huge, sole-sourced, power-hog, bad SPST switch for about 20x the price per contact of a good little telecom-type relay, with horrible thermal errors as a side benefit. The mercury-wets are toxic and position sensitive, and the dry reeds are fragile and unreliable. Both have mag field sensitivities.
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John Larkin Highland Technology, Inc
lunatic fringe electronics
HV supplies (low power of course) call for expensive HV reed switches in some instances. Not recommended as a best practice if an avoidance can be cheaply engineered in.
A big pain in HV design was setting up a customer with a single supply which he then used in either polarity, and we set up the switchworks for it all by his request. Explicit "changeover only when NOT energized" rules were explicitly given and requirements that he sign off that he was aware that live use would result in failure. I think it was like
6kV. Why he did not want a dual supply setup, I do not remember.
He made it about three months before he had to send it back for servicing. Those relays are not cheap.
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