Computer Controlled System for Impedance Measurements

Setup for impedance measurement based on AD5933 impedance convertor was accomplished and tested with a measurement of control samples. Introducing an external clock generator allows to extend the excitation frequencies in the range of 1 00 Hz÷50 KHz. An external analog front end schematics was added to reduce the output impedance and facilitate the measurement. The external analog front end includes low pass filter, voltage follower and current to voltage convertor. The measurement performed is in a good agreement with data taken from control impedance analyzer. The noise and signal distortion is considerable reduced using galvanic insulation between the personal computer and microcontroller from one side and the AD5933 impedance converter and the analog front end from the other. The relative error with respect to reference calibration resistors is within the range of ±0.5 %. A stability test shows that the change of the impedance with the time is less than 10 %, measured over 60 hours. A measurement of ionic liquid used as a simplified biomedical impedance model is with a good compliance with data, taken from a precise impedance analyzer.