Various types of humidity sensors operating on the capacitative principle are known. Usually, a plastic foil is provided which, reversibly, is capable of accepting and giving off water vapor. Upon change in the water vapor retained by the foil, the capacitance of the sensor with which it is connected will change. The change in capacitance is evaluated by a capacitative sensing circuit, for example a capacitative measuring bridge.
Sensors of this type are mechanically sensitive since polymer foils are used therein. The electrodes used with such a sensor are, at least in part, vapor deposited on the polymer foil. Manufacture of such sensing elements, hence, is expensive. Sensors of this type are thus not suitable structures for mass production or mass use. It has been found that in ranges of high relative humidity, that is, humidity of 90% or more, erroneous measurements can be obtained due to secondary sorption effects, which remain within the foil and are not readily dissipated even if ambient humidity should drop.
USPTO Backgrounds
USPTO Backgrounds