Calibration of Multi-frequency EIT System

Abstract

Multi-channel multi-frequency electrical impedance tomography (EIT) system requires a careful calibration method to minimize systematic errors. We describe novel calibration methods for the recently developed KHU Mark1 EIT system. Current source calibration includes maximization of output resistance and minimization of output capacitance using multiple generalized impedance converters. Phase and gain calibrations are used for voltmeters. Phase calibration nulls out the total system phase shift in measured voltage data. Gain calibrators are performed in two steps of intra and interchannel calibrations. Intra-channel calibration for each voltmeter compensates frequency dependency of its voltage gain and also discrepancy between design gains and actual gains. Inter-channel calibration compensates channel-dependent voltage gains of all voltmeters. Using the calibration methods described in this paper, we could obtain 1 MΩ minimal output impedance of the current source in the frequency range of 10 Hz to 500 kHz. The reciprocity error of about 0.05% was achieved after intra- and inter-channel voltmeter calibrations.