I want to know the capacitance of two surfaces. Therefore I applied a DC voltage across the surfaces. Then disconnect the supply and using an oscilloscope to check the discharge curve. The waveform is attached. I found that the initial voltage is 1.53V, the final voltage is 0.3V, the time used is 480ns (nano-second).

How can I calculate the capacitance from this waveform?
Thank you very much.

 

hi eepty,
Assuming the scope resistance is the only current discharge path, do you know current path resistance.?
E

Update:
LTS sim of discharge, probe load resistance = 1meg and 10meg.

 

Why don't you just measure it with a Capacitance dvm...?

 

You know Vo, Vc, t, R, solve for C.

Regards, Dana.

 

Thanks all.

Why don't you just measure it with a Capacitance dvm...?

I have also think of this method. In fact, it is a senior colleague asked me to conduct this test. I will ask him why. Also, I realized that the capacitance is very small, maybe we do not have a good LCR meter to measure such small capacitance.

You know Vo, Vc, t, R, solve for C....

Yes thank you. I have also calculated by a simpler formula. As 5RC is almost equal to fully discharge the capacitor, I just calculate the capacitance from: 5RC = 480ns

 

Are the two surfaces configured and made for capacitance? If not, you could be measuring more than capacitance.

Instead of measuring discharge.......why not put an AC signal of interest, and measure the capacitance.