Test Bench to Validate Audio CODEC Kit as EIT Complex Voltage Measurement Circuit

A simple bench test instrument was developed to measure the real part of the impedance of a patient simulated by a phantom (variable R 350-600 ohm in parallel with C=47nF). The instrument is part of an EIT design which includes a EVM-L137 evaluation kit to enhance previous designs. The DSP included in the kit generates the waveform to control current sources. We use this original signal as a time reference to measure voltage phase, thus minimizing unknown delays. Once data are corrected by a linear fit to remove systematic errors in measurement, the values obtained deviate on average 0.9% from the expected. This instrument will allow to further compare design options in EIT circuit development.