Richard Mark Dowdeswell

An intelligent gas sensing system

Electrically conducting organic polymers are widely used as a means of gas, odour or aroma analysis using multi-element array techniques coupled with direct current (d.c.) interrogation techniques. Recently it has been established that the use of alternating current (a.c.) interrogation gives rise to improved performance. In addition, the need to use multi-element arrays is much reduced since a single sensor can be interrogated at a wide range of frequencies. This gives rise to much increased information content for the measurements. This paper describes the use of alternating current (a.c.) interrogated conducting organic polymers coupled with neural network pattern recognition techniques for a system to determine the compositional fraction of volatile vapour mixtures. Experiments have been conducted on binary, tertiary and quaternary mixtures of vapours and compositional fractions have been determined to within 5%.

Pseudo-random binary sequence interrogation technique for gas sensors

Abstract Electrically conducting organic polymers are widely used as a means of gas, odour or aroma analysis using multi-element array techniques coupled with direct current (d.c.) interrogation techniques. Recently, it has been established that the use of alternating current (a.c.) interrogation gives rise to improved performance. In addition, the need to use multi-element arrays is much reduced since a single sensor can be interrogated at a wide range of frequencies. This paper describes the use of pseudo-random binary sequences (PRBS) as interrogation signals for semi-conducting organic polymer gas sensors. Preliminary experiments have been conducted upon volatile vapours and results are presented herein.

Frequency counting interrogation techniques applied to gas sensor arrays

Abstract This paper presents a simple, elegant interrogation technique for conducting polymer gas sensor arrays which takes advantage of their resistive and capacitive properties. To accomplish this, a four-channel Wien bridge oscillator system has been designed and constructed in which the conducting polymer sensor forms one of the arms of the bridge circuit. As gas or odour molecules adsorb and desorb from the sensor surface, the resistance and capacitance changes cause a consequent change in the Wien bridge oscillator frequency which is readily measured. Results of experiments using several volatile species are reported herein. Methods of improving the sensitivity of the oscillator-based approach have also been investigated and preliminary results of these investigations are also reported. The approach that has been adopted is applicable to any other form of sensor where the electrical properties change in response to a stimulus. Many other forms of phase shift oscillator can also be employed.