Development and performance of the gas sensor system

Abstract

The design, development, laboratory testing and production of the gas sensing instruments for the Heavy Gas Dispersion Trials are discussed in detail. The gas sensing transducer used in these instruments is an electrochemical cell which gives a signal proportional to the partial pressure of oxygen in the atmosphere. Any gas species is thus detectable by the reduction in oxygen partial pressure caused by its presence. The specification of the instruments and the factors influencing the selection of the electrochemical cell are discussed. The principle of operation of the cell is described, together with the main conclusions of a mathematical analysis for diffusion of oxygen molecules through thin membranes. In order to achieve the required frequency response, an electronic signal-enhancement technique was developed. The basis of this technique is explained and experiments are described which confirmed its effectiveness. The instruments were subjected to laboratory performance checks before delivery to the trials' site. Details of these checks and the results obtained are presented. In order to assure the accuracy of the data produced by the gas measuring system, the on-site performance of the instruments was checked at regular intervals by applying known gas mixtures. The performance of the instruments is discussed and certain design refinements are described. The quality of the data produced by the gas sensing system is of key importance and techniques were developed to validate the data before their release to sponsors. The validation methodology adopted is described. The instruments have performed reliably with minimum maintenance. They are low-cost devices and are capable of working over wide temperature and humidity ranges.