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#177445 - 05/02/08 08:40 PM Capacitive Proximity Switch
BigJohn Offline
Member
Registered: 03/06/04
Posts: 391
Loc: 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 07:52 AM Re: Capacitive Proximity Switch [Re: BigJohn]
twh Offline
Member
Registered: 03/11/04
Posts: 901
Loc: 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.
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#177513 - 05/05/08 05:55 AM Re: Capacitive Proximity Switch [Re: BigJohn]
LarryC Offline
Member
Registered: 07/05/04
Posts: 780
Loc: 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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