A TEST SYSTEM FOR GAS SENSORS

An important instrument in the development of gas-sensor systems and pattern-recognition methods is the test and measurement system itself. Whereas prefabricated gas mixtures are often used for calibration of commercial 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 humidification at a high dynamic range. Gas mixing is performed via a volumetric method. An overview about the calculations necessary for the volumetric mixing is given. Two test chambers have been developed, optimized for a small volume and a precisely defined gas stream. These test chambers simultaneously contain up to ten sensors of different types (semiconductor, dielectric, microbalance, etc.) and provide measurements 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 demonstrate the quality and flexibility of the test system.