A suitable low cost electro-chemical cell for the sensing of carbon monoxide became available in the year 1991. A project was commenced to evaluate the development of equipment with low capital and operational costs but capable of simultaneous traffic measurement. The development programme, consisted of: (1) the integration of the electro-chemical cell; (2) temperature conditioning of the cell output; (3) case design (portable and fixed); (4) microprocessor hardware and firmware; (5) data transfer (direct and via modem); and (6) a presentation graphics system. The concentration levels of interest, (0 to 400 ppm), require that the signals from the cell are to be adjusted as a function of temperature. The meaningful presentation of both traffic and pollution data was addressed by addition of graphical outputs. Performance and reliability were independently assessed by a certified test laboratory. The evaluation of both linearity and drift was included. These are considered to be important factors affecting performance. An urban and rural authority undertook field evaluations and compared the data with existing background monitoring sites. Field testing yielded feedback on the design, and resulted in adjustment to the equipment controls. Data from the existing equipment and the new design was compared, particularly in respect of peak measurements. The effectiveness of the new equipment for finding high concentrations of pollution, or 'hot-spots', was assessed. (A)
Samenvatting