SENSITIVITY ENHANCEMENT FOR GAS-SENSING AND ELECTRONIC NOSE APPLICATIONS

The sensitivity of varistor types of gas detector may be severely rest ricted by conventional techniques of deriving the system input signal from a voltage change arising from a dual-arm potential divider. A muc h more effective means of analogue signal processing for high sensitiv ity can be achieved through the use of a.c. bridge methods, together w ith narrow-band filtering to enhance the signal-to-noise ratio. Such m ethods have been applied to commercial tin dioxide sensing devices int ended for use in an electronic nose and we present results showing the m to give sensitivity improvements of about two orders of magnitude, w ith an expectancy of further improvement following circuit refinement. The techniques are equally applicable to the sensing of individual ga ses, gas mixtures or complex odours.