A TEST SYSTEM FOR GAS SENSORS

An important instrument in the development of gas-sensor systems and p attern-recognition methods is the test and measurement system itself. Whereas prefabricated gas mixtures are often used for calibration of c ommercial gas sensors, research purposes need a more flexible system. The test system of the Fraunhofer-Institute for Solid State Technology (IFT) provides independent mixing of two test gases together with hum idification at a high dynamic range. Gas mixing is performed via a vol umetric method. An overview about the calculations necessary for the v olumetric mixing is given. Two test chambers have been developed, opti mized for a small volume and a precisely defined gas stream. These tes t chambers simultaneously contain up to ten sensors of different types (semiconductor, dielectric, microbalance, etc.) and provide measureme nts of gas temperature and pressure. The exhaust gases are analysed by a dew-point mirror and an optional infrared gas analyser to check the gas combination and accuracy of gas concentration. Measurements with semiconductor sensors, dielectric sensors and microbalances demonstrat e the quality and flexibility of the test system.