Measuring small levels of capacitance

Discussion in 'General Electronics Chat' started by shaun8567, Nov 24, 2010.

1. shaun8567 Thread Starter New Member

Nov 24, 2010
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I working on my senior design project, and I need a way to measure very small levels of capacitance (as well as change in capacitance). The capacitor will be on the order of picofarads (at the moment the capacitor I am going to make will vary between 15-25 picofarads), and I haven't been able to find a method to accurately measure levels this small.

I did run across a variation of a Wheatstone bridge that uses capacitors:

where the change in capacitance can be described by:

However, the book is not clear on what Cv(0) is (in the numerator). Is that the value when the variable capacitor is the same as the other capacitors in the bridge?

Does anyone else know of any other method for measuring capacitors on the picofarad level with sub-picofarad resolution?

2. Jaguarjoe Active Member

Apr 7, 2010
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This might give you push in one direction:

http://www.easyeeg.com/previousMeasurements.html

Another way would be to build a charge amplifier. It would require an IC like above and one reference capacitor of a known value similar to that which you are measuring.

3. jpanhalt AAC Fanatic!

Jan 18, 2008
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shaun8567 likes this.

Nov 24, 2010
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Jan 18, 2008
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6. Nate Marsh New Member

Nov 20, 2015
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bringing this back from the dead because this is the ONLY bridge on the internet with 4 caps (that I've found)

Any ideas on the change in capacitance formula? What could the v0 in the numerator be? I'm dealing with a bridge comprised of 4 caps and want to determine the output voltage formula.

7. BR-549 Well-Known Member

Sep 22, 2013
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Last edited: Nov 20, 2015
8. alfacliff Well-Known Member

Dec 13, 2013
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you could build an lc oscilator and measure the frequency, thats the way some testers do it. be carefull on lead lengths and layout, when the measurement is getting close to the parasitics in the circuit, strange readings occure.