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How do I measure an unknown impedance with the AD5933?

Question asked by harshita on Feb 22, 2012
Latest reply on Oct 13, 2013 by wpsword

I just got the EVAL-AD5933EBZ board. I have been trying to calibrate it correctly to measure resistance. I tried calibrating with a 150kohm resistance and measuring 200kohm with it. This works and I have attached an image of the results. Then I also tried calibrating with 27kohms and measuring 33kohms but the values I am getting are nowhere close to 33kohm. I am getting a measurement of 135 ohms. This can be seen in the second image.


This is what I do to use the device:


First I insert the calibrating resistor into the "CAL" resistor slot on the board and type the value of the resistor into the "Resistor value R1" section of the program. Then I program device registers and calculate gain factor.


Then I insert the "unknown" resistance into the "Z" resistor slot on the board and start sweep.


Am I doing this wrong? Also, I tried different sweep parameters to try and see if I could get a better measurement that way, but that did not really make a difference.


If someone could please give a step by step procedure as to how they use the AD5933EBZ evaluation board that would be of great help.