> This brought me to understand a little-known property of mechanical
> switches, called "wetting current".  This is the minimum current 
> required
> for the switch to actually be closed.   When I found out about this, 
> I
> increased the loop current used in the system from about 2mA to 
> about 20mA
> and the problem dissapeared.    This mod was reported back to 
> Litton, and
> incorporated into the design of the control interface, apparently we 
> weren't
> the only ones having problems.

AFAIR (possibly wrongly) Gold has a *higher* wetting current 
requirement than some other less expensive contact materials.


        Russell McMahon

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