ABSTRACT
As it is well known, one of the most important parts of any gas measuring system, if not the most important one, is the sensor. Therefore, the sensor choice is a basic part of the detector development. An initial program of exhaustive test of different pre-selected commercial sensors was planned to choose the ones with best characteristics. As our application combines detection of carbon monoxide and methane, we have considered sensors able to detect both gases. Lately, a number of manufacturers offer sensors that permit the simultaneous detection of CO and CH4 (FIS, Microsens, MICS ...). These sensors operate in a pulse mode changing the working temperature with a period of time of 10 to 15 s. CO is detected on low working temperatures ranging from 80°C to 200°C, while methane detection is usually performed on temperatures between 400°C and 500°C, although detection at the low temperature has been also proposed. . The presence of active filters enhance their selectivity characteristics, but on other side can bring problem of filter poisoning after a long presence of some gases like i.e, ethanol. Apart from the sensitivity and selectivity, characteristics like temperature and humidity dependence as well as inter-variability between sensors have also been considered as the important point in final choice.
