Digital correction techniques for accuracy improvement in measurements of SnO/sub 2/ sensor impedance

In this paper, the performance improvement of a gas-sensing system by digital correction techniques is discussed. The considered system operates as a vectorial impedance meter and performs impedance measurements of eight sensors arranged in an array in the frequency range 10 Hz-15 MHz. The measurements of the chemical sensors' impedance is an innovative technique that allows highlighting different adsorption mechanisms taking place when the sensors are exposed to gases. Of course, impedance analyzers are commercially available, but they usually make measurements on only one device at time and they are very expensive. The proposed PC-based impedance analyzer is a versatile one and shows good performances for gas-sensing applications. A digital correction technique is used in this work to improve the impedance measurement accuracy of each channel of the gas-sensing system (eight sensors /spl rarr/ eight channels), in order to compensate for the conditioning electronics response. The latter is evaluated in a characterization procedure. A linear black box two-port model is used to take into account crosstalk, amplitude, and phase distortions. Two different techniques to evaluate the response of the measurement system are discussed in this paper, and experimental results are presented on both the measure of reference impedances and on the measure of chemical sensors.