PIEZOELECTRIC MOISTURE MEASURING DEVICE

A moisture-measuring device for measuring moisture of the ambient on one side of a solid wall (16) comprises a piezoelectric crystal (22) sonically coupled to the wall (16) on a surface thereof facing the one side. A capacitor or other moisture sensitive impedance means (30) is connected to the piezoelectric crystal (22) over a network (28) which is operable to provide a response indicative of the impedance of the capacitor or other impedance means upon excitation of the crystal at the resonant frequency of the circuit. The capacitor (30) comprises at least two spaced plates (32, 34) which are exposed to the ambient. Change in moisture in the ambient thus causes change in capacitance of the capacitor (30). By sonically exciting the piezoelectric crystal (22) from an opposite side of the wall, a measure of change in resonant frequency of the network (28) can be made. This measurement is related to the moisture content of the ambient.