Repeatability Describes the ability of a sensor to repeat its performance in a number of tests. Stability Gives an indication of drift over a period of time. Temperature dependence Shows the effect of temperature change on the RH output value. Over a large temperature range this change can be substantial. In Vaisala products the temperature compensation built in.
Response time Is the speed of response of the sensor when subjected to a step change in humidity.
This varies depending on the temperature, air flow and type of filter fitted. A typical response time with Vaisala products is 15sec. Vaisala produced the World s first thin film capacitive humidity sensor in 1973. The principle of operation of the sensor is based upon a change in capacitance as a polymer film absorbs and desorbs water vapor. The input stage of the transmitter electronics must also be capable of measuring this small non linear capacitance change with good accuracy and repeatability.