A novel type of gas-sensing technique has been developed by combining a gas-diffusion membrane with a gas thermal conductivity sensor operating in a cyclic mode. The small volume enclosed between the diffusion membrane and the thermal conductivity sensor is periodically flushed with a purge gas. After each purge cycle, the thermal conductivity reading gradually changes from the value of the purge gas to that of the gas to be measured. The rate of change is continuously monitored and is a direct function of the concentration of the gas to be measured. Thanks to the hydrophobic diffusion membrane, the sensor can also be used for measuring dissolved gas in almost any liquid in a wide range of temperature and pressure. A simplified theoretical model has been established and experimental results will be presented for the measurement of CO2 in N2, N2 in CO2 and H-2 in N2. Comparisons with an amperometric sensor will also be given.
