Robust acoustic humidity sensor for industrial drying

Most conventional humidity sensors are unfortunately sensitive to extreme process and environmental conditions. This paper concerns the development of a robust acoustic humidity sensor which can be used even under extreme conditions, such as high temperature up to 300/spl deg/C, aggressive, explosive or toxic pollutions in the gas to be analysed, dust, electromagnetic disturbances, nuclear radiation or very fast changes of the humidity concentration. An important application of the sensor is the in-situ measurement of humidity in the exhaust air of industrial driers for paperboard production.