Multi-parameter monitoring of binary gas mixtures: Concentration and flow rate by DC excitation of thermal sensor arrays

This contribution presents a thermal sensor, which is capable of simultaneously determining gas concentrations of a binary gas mixture under flow conditions and its flow rate. The sensor design corresponds to the calorimetric principle. The multi-parameter detection is achieved by the use of two time independent excitation modes (power and temperature). Due to the developed sensor design, a flow independent, but gas sensitive region is obtained in power mode. In this flow range, the thermal conductivity is measured by analyzing the temperature of the downstream element. Gas concentration of the binary gas mixture is derived from the theoretical relationship to thermal conductivity. Afterwards, the flow rate is detected by evaluating the temperature difference between the down- and upstream temperature sensors in temperature excitation mode. This measurement technique has been successfully proven under laboratory conditions, where a flowing mixture of e.g. methane and carbon dioxide has been analyzed. The carried out measurements show an accuracy of ±5% in gas concentration and of ±3.3% in flow rate. This measuring method seems to be sufficient to analyze biogas in anaerobic distinctions. However, further investigation is needed to open this technique for this application.