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AD5933 Reading Error on Resistor

Question asked by br500 on Nov 9, 2016
Latest reply on Jan 4, 2017 by br500

Utilizing the AD5933 eval board, I followed the app note and datasheet example with th 200k resistor as a cal and Rfb. That is shown in the 200k_Calibration photo. I let the s/w calculate the gain factor. Resistor Zload is the breakout box on the left. Board is in the center. Scope shows in yellow excitation at the op amp A1 output. Blue shows voltage at Rfb. Pic Setup shows detailed hookups. 200k R is composed of 2 100k resistors.

Then, I connected the 510k Ohm and it read 640k.

I played around with various configurations like 100k, 10k, Vexc Vpp settings and always results where off after calibration. Always paid attention that the input (blue channel) was not saturating op amp.

Any idea what am I doing wrong here?

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