I am using a EVAL-AD5933EBZ to measure resistance or capacitance. When I use 220k resistance for RFB and Z to calibrate. After calibration, I moved the 220k out of Z and leave the 220K still in the RFB. When I put a resistance that is bigger than 120k, the results are good. But when put a resistor of lower value, like 82k, the results are strange.
Also for the capacitor measurement, after calibration using 220k resistance, 33pF or lower value capacitance can be measured. But capacitor bigger than 33pF turns out weird results.
The excitation frequency is from 49900-50100Hz.
Can anyone give me suggestions on this? I appreciate it a lot.