A new method for membrane-based gas measurements

A method for gas measurement based on selective diffusion of gases through membrane tubes has been developed. Combining the element-specific diffusion rates through a membrane set and Dalton's principle of partial pressures, the gas concentration is determined through measured physical quantities: pressure, time, and temperature. Since the procedure is based on the evaluation of an intensive thermodynamic state variable, miniaturization of the sensor is possible. The gas sensor consists of several measuring chambers closed by membranes, where each chamber has its own pressure sensor. One additional sensor is used for temperature measurement. The measurement is carried out after the conditioning of the measuring chambers with a purge gas, which is used as internal standard. In order to determine the m partial pressures of the components by n pressure measurements, a system of linear equations has to be solved. The measuring method is demonstrated for a two-component-gas phase (oxygen, nitrogen) for a partial pressure range from 0.1 to 100 kPa. The mean absolute error of about 5% related to the measurement value is acceptable and can be reduced further, if the technical deficiencies of the experimental set-up are improved.