Re: gEDA-user: Contact reliability

[Bob Paddock <bpaddock@xxxxxxxxxxxx>]

On Wednesday 19 January 2005 01:41 pm, Karel Kulhavy wrote:

> What are the conditions under which 100% reliable contact between two
> metals is guaranteed? My hypothesis is that there are only two
> possibilities:
>
> 1) gold-to-gold
> 2) The touch point is under permanent great preload

You could try some of this new Peratech material:

http://www.peratech.co.uk/pills.htm

The follow discusses switches, but the same idea could apply to a
bulk-head style connector.

They have some other cool products as well.  Seems to be a material in search 
of an application...

"
Retrofittable Components for Improved Switching Performance

The basic design of low power switches has not changed substantially over many 
years. However the advent of QTC now allows switch manufacturers to easily 
add new functionality to existing switch designs or to develop new, simpler, 
more reliable designs. 

Making Contact

Most mechanical switch designs involve the physical coming together of two 
contacts to complete the circuit. QTC allows a different approach to be 
taken. QTC is essentially a non-conductor in its normal state. However, under 
pressure, QTC starts to conduct and under sufficient pressure its resistance 
drops to less than 1 ohm. 

This property allows switches to be constructed that essentially have no 
contacts. However, it also allows for improvement to existing designs by 
interposing QTC Pills between the existing contacts in a switch. 

Soft Start

Because QTC’s resistance doesn’t drop instantly but drops away exponentially 
as pressure increases, this enables the current through the switch to slowly 
increase as the switch is closed, giving a soft start. 

No Arcing

The same mechanism, combined with the fact that there is no physical contact 
gap required, serves to ensure that there is reduced possibility of arcing, 
which improves safety and contact life. 

Proportional Control

The gradual drop in resistance described earlier allows for a standard switch 
to offer full proportional control of a load. An existing momentary 
spring-loaded switch can be ‘upgraded’ to provide proportional control simply 
by inserting a QTC Pill between the existing contacts. Direct uses therefore 
include, for instance, controlling the speed of a motor or brightness of a 
lamp. "