High-speed multichannel impedance measuring system

Abstract

In this paper, a novel high-speed multichannel impedance measuring system in presented. The measurements are based on simultaneous excitation with two distinct frequencies to interrogate the multiple sensing point of a given sensor. Received signals are analogue-to-digital converted (with a DAQ card) and the amplitudes of each frequency are determined using FFT implemented in LabVIEW. The capacitive and conductive parts of impedance are calculated based on amplitude measurements. The developed system can operate 8 transmitter and 8 receiver electrodes at a frame repetition frequency of up to 781 Hz, i.e. single channels are sampled at 6,248 Hz. The system has been evaluated by measuring reference components. Deviations from references values are below 10% which considering the fast repetition frequency of measurements is satisfactory. The developed system was applied to visualize the fluid distribution over the surface of planar multipoint sensor. Two different liquids (oil and water) and air were evaluated and their spatial distribution over the sensor’s surface was correctly visualized.