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AD5933: Inaccurate impedance measurements for first (few) frequencies of frequency sweep

Question asked by terencech4n on Apr 30, 2018
Latest reply on May 1, 2018 by Snorlax

The frequency sweep I am performing is starting at 2kHz, with roughly step sizes of 2kHz for 50 increments. Using a 100 ohm resistor for calibration, the calibration values seem pretty consistent, but when measuring larger values like 200 ohm - 1k ohm, the first few frequencies of the sweep (i.e. 2kHz, 4kHz, etc.) are way off, both for the magnitude and phase. The other rest of the sweep looks fine. 

 

For smaller resistances, the difference (between expected and measured resistor value) for the first frequencies are smaller,/'acceptable' but the larger the resistance, the difference is magnified more. 

 

Any suggestions on how to fix this or why this is occurring?

 

Current setup is using 400mV p-p range, PGA gain = x1, and I am following the frequency sweep procedure on pg 22 of the datasheet.

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