AVR-Chat

No electro-mechanical switching device will do well with less than a 
very few micro amps, but with those really eensie weensie currents found 
in what's considered to be a "dry" circuit, less than 100 micro amps, 
the contact pressures must also be high.  For dry circuit applications 
there are a variety of schemes used depending upon other mechanical 
needs.  High contact pressures and contact alloys are the primary 
mechanisms used to ensure reliable low current operation.  Contact style 
is also a factor from time to time.

I can see where a vibration sensor would need to have small contact 
pressures in order to operate properly.  I thought most vibration/shock 
sensors these days are piezoelectric devices.

"Bifurcated contacts" always sounded a little nasty to me.


REB



David VanHorn wrote:
>> Silver alloys are fine for "power" applications but they're severely
>> limited when you get down in the mud with really low currents because
>> the contacts will build up an oxide or a sulfide coating.  This is why
>> they depend on the small amount of arcing that will occur in a power
>> circuit.  At low currents, such as driving a logic input, you'll need
>> gold inlay or a gold flask over silver contacts.  The same holds true
>> for relays.  Be sure to9 look at the minimum current ratings for
>> switching devices.  There's also a difference between switching current
>> and carrying current capacities.
>>
>>     
>
> It's called "wetting current" and even gold-on-gold needs some small current.
> Litton made that mistake with their first shock sensors for glass break.
> The switches would stay closed for hours or days or weeks, then open
> up for a few seconds for no apparent reason.
>
>   


[Non-text portions of this message have been removed]