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[AD5933]How to achieve high accuracy of impedance measurement with small capacitor?

Question asked by sofy Employee on Sep 16, 2014
Latest reply on Sep 19, 2014 by musach

Hello,

When trying to impedance measurement using EVAL-AD5933EBZ for R//C network, EVAL result is about 30% over value than a commercial LCR meter's result.

I would like to achieve more high accuracy.

 

Test conditions as below,

AD5933 output range is 0.2V (range 4)

Excitation freq 1kHz, MCLK 2MHz

     Note :Output range 0.2V (range 4) and excitation freq 1kHz are not able to change another value due to the customer's application.

PGA x5

Rfb 470ohm or 820ohm

Rcal 1kohm

Targeted  Resistor range is 100ohm to 980 ohm, and Capacitor range is 0.2nF to 1350nF.

 

Bad result (accuracy was 30% over than commercial LCR meter), when target Capacitor were 0.2nF, 1nF, 5nF.

Good result (accuracy was +/- 1% than commercial LCR meter), when terget Capacitor was 400nF.

 

I would appreciate if you have any advice to achieve more high accuracy when measurement small capacitor with parallel R network.

 

Best regards,

Sofy

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