capacitive height sensing

C

Thread Starter

cheetah

whats the technical procedure to use the capacitance of a metal ring to measure the distance of the ring from a metal plate. I succesfully implemented a circuit to measure capacitance, but it doesnt seem to work because capacitance of the ring doesnt change with height from the plate. I must have missed some very very important point. does anyone know what?

thank you
 


It should, but in my design, it does not. I implemented a square wave oscillator using opamps, frequency is dependent on the input capacitance. When I change the capacitor values the frequency indeed changes. So there is no problem measuring the capacitance. But when I use plate and ring, capacitance seems to be constant and not a function of distance between two.
 
Hi.

Could you please inform if that circuit could be used for sensing areas between plates, separated about 2 inches?

Regards
 
M
Just to make sure, do you mean "distance between two plates" or "area of a plate"? ("areas between plates" has no physical or geometrical meaning to me).

You may want to consider:
The basic capacitor (air dielectric) formula, An oscillator where the variable capacitor determines the frequency, To you and the previous writer - consider stray capacitance - it can be so big related to the one measured - that the overall capacitance is practically constant.

Meir
 
C

Curt Wuollet

If the plates are large enough. I suspect the problem with the original was that the parasitic capacitance (cables, etc.) swamped the change.

Regards

cww
 
Top