Hello,
I am using Eval-ADUCM350EBZ board to measure impedance. My goal is to measure a difference in magnitude and phase of the unknown target in real time between 100~10kHz frequency range. What I am gonna measure should be capacitive, and the magnitude range is 1k~10k. Absolute accuracy is also important for me, but relative accuracy is more important.
FYI, I didn't change any component on the daughter board (Rcal: 1kOhm, Rtia: 33kOhm, Ctia: none, Raccess: 4.99kOhm, Rlimit: 3kOhm, Ciso: 47nF)
First, I tried 2-wire setup in IAR using the given 2-wire example code.
When I measured 1kOhm and 10kOhm, I could measure a correct result and the accuracy was good. However, If I switch to 1kohm + 220nF or a pure capacitance 220nF or 470nF, the measured value was wrong. In more detail, the results of 220nF and 470nF have a relationship between their values, but the absolute values were wrong. And for the 1kohm + 220nF, I could only see 1kOhm, which means the result was exactly the same as 1kohm.
My initial plan was to use just 2-wire setup because relative accuracy is more important for me. But the results of complex impedance measurement was bad, and now I am worrying to use this setup. I wonder if there is anything wrong what I did during the setup or measurement. I wanna know whether my setup is wrong, or I need to change some values or given code.
Second, I also tried 4-wire setup in IAR using the given 4-wire example code.
I tried to measure 1kohm, 10kohm, and 20kohm. But in this case, the absolute values were wrong. The magnitude values were like ~31.4 times higher at 1kHz. And phases were 180 degree. Especially, if I change the frequency, the mag and phase changed together, which I couldn't see during the measurement using 2-wire setup. I understood that 4-wire only concerns the impedance at the sensor node, so the frequency will not affect the measured value especially for my case with only resistance (1,10,20kohm). In this case, I also wonder if there is anything that I did wrong and have to change here. I wanna know whether my setup is wrong, or I need to change some values or given code.
FYI, I attached my setup photo. (black cable: for 4-wire measurement, red and orange cables: for 2 wire measurement)
