EVAL-AD5933 Basic Impedance Measurements


I got today my EVAL-AD5933EBZ board and have some issues with the first measurements. I followed the instructions in the guide of the EVAL board, but getting some strange results. Maybe I misunderstood some parts in the guide.

After installing the software (downloaded from the internet), I checked the configuration of the jumpers. Following configuration is active on the board:

LK1 = open, LK2 = open, LK3 = closed, LK4 = open, LK5 = closed, LK6 = A

To perform the first frequency sweep of 30 kHz to 32 kHz across a 200 kOhm resistor, I put in the sockets of RFB (left of R2 and above R4) a 200 kOhm resistor as feedback resistor. Additionally I connected the "unknown" 200 kOhm resistor to the Z sockets left of the place for C2.

I configured the parameters in the software and programmed the device registers. Then I performed a gain factor calibration by pressing "Calculate Gain Factor" and got 5.11035456561638e-10, which is similar to the value of the screenshot in the manual.

When starting a sweep I got following impedance curve:

When now replacing the "unknown" 200 kOhm by a 100 kOhm resistor, I get following results. Yes, RFB is still 200 kOhm.

The results is nearly the half of the first measurement, which I expect. But in both measurement I got a wrong exponent. Did I do something wrong during calibration? Is it software issue with Windows 7?

Thanks in advance.