Hi Guys,

Am trying to develop a circuit where am trying to get an approximate idea of distance by capacitive sensing. I have seen few products where a sensor ring (completely of steel) acts as a capacitor plate and its distance from a steel plate surface is tracked. There is no electrical connection to the steel plate. However, my question is how can just a single ring act as a capacitor. A capacitor can be formed only when 2 plates with a dielectric in between is given an AC vltg. Just not able to understand.

 

Welocome,
have a read of this attachment

 

Hello,

This page of the EDUCYPEDIA will give you several links on Capacitive sensors

Bertus

 

Not too useful guys

 

I'm not sure if this is too simplistic for you but I learned a lot about implementing a capacitive proximity sensor by watching this:

http://www.youtube.com/user/nerdkits#p/u/7/euv8ZLgPh8A

I built my own which uses a slightly different software implementation here:

http://www.youtube.com/user/jg1996business?feature=mhee#p/a/u/0/zbBPf3Xncdw

Regarding your comment above, is it possible that the steel plate shares a common ground with the circuit in which case I don't think it would need a wire connection?

 

No the system works even if i put my hand under the ring (due to the conductive nature of human skin) .. so dont think a separate ground is required.

 

No the system works even if i put my hand under the ring (due to the conductive nature of human skin)

Its not due to the conductive nature of human skin. Capacitive sensors work when the electric field is broken by anything, even plastic. I just set one up yesterday that looks through a piece of plexiglass to determine the presence of plastic pellets on the other side. This is possible by adjusting the sensitivity of it, so that the electric field is just strong enough to make it through the plexiglass. This is all outlined in the unuseful PDF I posted.