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'[OT] Mercury, was Re: Comments on keypad design?'
2006\01\03@221013 by Richard Prosser

picon face
> >> Anyone that thinks gold contacts do not corrode or get dirty
> >> should talk to telephone engineers in geothermal regions. I
> >> know the telephone exchange in Rotorua, NZ, went to extraordinary
> >> lengths to keep the sulphurous air out of the exchange back in
> >> the days of using relays. The area around Rotorua is very
> >> similar to Yellowstone Park in the USA.
> >
> >Presumably if you need a telephone exchange it means that
> >people live there, in this sulphurous atmosphere?
>
> Err, yeah, like a city full - which is minimum 20,000 in NZ, plus the
> surrounding environs. Constant rotten eggs smell, but nice hot pools.
>
>
We used to have to make special telephone cordage (curly cord etc.)
for Rotorua - using lead-free PVC. The standard lead based stabilisers
used to  make the cords go black after a very short time.

I think "mercury wetted"is different from a tilt switch. In the former
a mercury coating on the contacts is used as the contact material.
Presumably it stays there by either surface tension or by forming some
sort of alloy (or amalgum?).


RP

2006\01\03@222917 by David VanHorn

picon face
>
> I think "mercury wetted"is different from a tilt switch. In the former
> a mercury coating on the contacts is used as the contact material.
> Presumably it stays there by either surface tension or by forming some
> sort of alloy (or amalgum?).


Yes. I don't know the metal underneath, but the mercury adheres to it, and
forms a "wet" coating over the entire surface.
When the contacts close, the mercury flows over both. It also makes sure
this way that there is never a point contact.

When the contacts separate, they have to move far enough to pull the liquid
mercury apart of course.

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