Response And Compensation Of Temperature Sensors

An innovative technique to measure the thermal lag, or response time, of a cold-wire temperature sensor is presented and an electronic compensation scheme is developed for measuring temperature fluctuations to about 1000 Hz using commercially available sensors. In order to measure the response accurately, a new methodology, utilising pulse heating of the sensor with a chopped laser beam, is illustrated. The square-wave energy pulse produced by the optically-chopped laser beam is sensed by the wire and its output is fed to a spectrum analyser for determining the high-frequency roll-off of the sensor. From these data, the time constant of the given sensor may be determined at various mean air velocities. The measured 3 dB frequency point is compared with the theoretical response equations derived for each sensor. An electronic compensation circuit is described which corrects for the high-frequency roll-off of the temperature sensor as a function of mean air velocity. The scheme provides a real-time response correction to the output of the temperature sensor in a fluctuating medium over a velocity range of 0-10 m s-1