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#177445 - 05/02/08 11:40 PM Capacitive Proximity Switch  
BigJohn  Offline
Member
Joined: Mar 2004
Posts: 391
Boston, MA
I need a hidden deactivation switch for a security system. I'm thinking of using a capacitive proximity sensor hidden behind a thin, non-metallic object that will activate a relay when a hand is passed over the object.

I've never worked with prox. switches before. It appears that most of these switches use a transistor for switching. Are these traditionally digital or analog outputs? Will putting a barrier in front of the switch cause it to constantly conduct some amount of current to the output (maybe in relationship to the distance of the object from the sensor)? Or do most of these have a threshold value for "on" or "off"?

Any help would be much appreciated.

-John


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#177463 - 05/03/08 10:52 AM Re: Capacitive Proximity Switch [Re: BigJohn]  
twh  Offline
Member
Joined: Mar 2004
Posts: 918
Regina, Sask.
The ones I'm most familiar with are a two-wire switch. Typically, they would provide an input to a PLC, but I've used them to switch a small relay.

Put a barrier in front of it and it will change states very quickly. The distance is adjustable. Metal is quite easy to calibrate, grain is harder to calibrate and needs to be in direct contact, and a hand - I've never had a bin full of hands, but I'm quite sure that I've tripped them with my hand.


#177513 - 05/05/08 08:55 AM Re: Capacitive Proximity Switch [Re: BigJohn]  
LarryC  Offline
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Joined: Jul 2004
Posts: 783
Winchester, NH, US
Most prox switches I have worked with have a sensitivity adjustment. Metal sensing prox switches would work if the user wears a ring or holds keys or a tool up to the surface.

Larry C



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