Capacitance Meter

[Kelkan]

Im looking for a way to measure capacitance..in the pico farad range with at minimum .1pf precision..ive looked at using a 555 timer but found the precision to be greatly affected due to tempreture and interal drift inherent in the 555....

any suggestions would be greatly appreciated...the circuit must be of minimal power consumption and cost ..therefore looking for something that can be surface mounted

 

[VEBill]

You're looking for a circuit technique, or an off-the-shelf instrument ?

 

[maged541946]

.1 pf resolution, you did not say what accuracy, eg if you display 2.1 pf is it +/- 1 count (+/- 0.1pf) or less than that....?
now what is your maximum range, you then deside on high quality crystal to do the job
the major problem would be the wire capacitances because it is in the range of few pf's, you need to compesate hor those too.
Pf range needs higher frequency than commercial product like 555 can provide

Maged A. Mohamed

http://magedm.freeyellow.com

http://www.magedsoft.com

 

[cbarn24050]

You need a capacitance bridge, a bit like wheatstone bridge. You can go for a nulling tecnique or measure the offset voltage from the bridge. The big problem is balancing out stray capacitance.

 

[Warpspeed]

As others have pointed out, stray capacitance is going to mask what you want to measure.

Probably the only technique with enough sensitivity would be to connect the unknown capacitance to a high frequency LC oscillator circuit working up in the tens or hundreds of Mhz range, and note the change in oscillation frequency.