# How to measure capacitance of a capacitive sensor?

I've started working on capacitive sensors and finally got one ready(which is concentric cylinder type) but now I need to test it. I have few doubts:

1. Can I calculate the value of capacitance without any instrument? May be just with an analytical formula.
2. What difference I may get in the values of capacitance produced from this formula and from an LCR-meter?

• please provide a picture / drawing of your sensor. If you don't have enough rep someone else will edit you Question. – placeholder Jun 29 '16 at 15:12

Or better yet: R is for bias current and should be large.

The way a multimeter calculates the capacitance of a capacitor is by using an integrator operational amplifier.

However, in real terms, it is:

But if you really don't want to use any measurements, it would be best if you look at the product specifications. Any difference between the calculated and actual capacitance is very small, if it's in good condition.

The circuit of an integrator op amp is as follows below.

simulate this circuit – Schematic created using CircuitLab

• This works in theory but in practice you need to cap the gain with a resistor in parallel with the capacitor. – lucas92 Jun 29 '16 at 16:09

I'd drive it with a known AC voltage source, measure the AC current. (Maybe with a TIA opamp circuit if the capacitor can float and the frequency is not too high.) Then do the math to calculate the capacitance. (Extra credit for synchronous detection of the current.)

Actually, today the most practical way is to take a capacitance to digital IC, like FDC2214.

• yeah ok but im working on sensors and trying to develop one.Just want to know that can we compare LCR meter reading and the formula based result?? – Siddharth Bardiya Jun 29 '16 at 16:33
• If your working with unknown capacitors and/or inductors you should buy an LCR meter. I bought one for about \$400 USD just to be certain of unlabeled parts.@Gregory Kornblum. In the future please provide a better answer by offering options, both cheap and expensive. A one sentence answer could get deleted. – Sparky256 Jun 29 '16 at 21:55