I have been running long term tests of my system using the AD5933 and Multiplexers to analyze different complex impedance elements. For my current test I'm only looking at 1 of the elements and leaving the others multiplexed to nothing. This means that, when we are not on the scan we care about, the multiplexers should be switched to form an open circuit.
I'm getting some values back from the AD5933 that are always close to the calibration resistance, even when I make the impedance I'm looking at to be distinctly different from the calibration resistance. I was wondering if this is an error in my uC's firmware, or is this behavior expected when an open circuit is formed once the gain factor has been obtained off of the calibration circuit?
I would expect if a scan was left floating, the values received from the AD5933 would be all over the place, rather than sitting right around the calibration resistance. Any insight on this phenomenon would be much appreciated.