GB1520133A - Device for measuring the moisture content of a material - Google Patents

Abstract

1520133 Measuring moisture electrically CLAAS MASCHINENFABRIK GmbH Gebr 30 July 1975 [30 July 1974] 31888/75 Heading G1N In a capacitive moisture measuring device of the type in which spring-biased measuring capacitor 13 is connected in a resonant circuit 11, 12 to which energy is supplied from an adjustable external oscillator 10 the reactance of the capacitor 13 is made large e.g. 1:100,000 with respect to the remaining reactance of the resonant circuit so that the admittance of the material under test has a negligible effect on the current or voltage in the resonant circuit compared to the changes due to changes in the moisture content of the material. The resonant circuit and the frequency of oscillator 10 are adjusted so that with a certain moisture content of e.g. straw between and in contact with the polished contact surfaces of the electrodes of 13 the voltage across or current through load resistor 4 is zero. A change in moisture content results in the circuit being shifted away from resonance and the resultant voltage or current is rectified 15, amplified 16 and fed to indicator 17. Capacitor 13 is preferably situated at least ten times its inter-electrode distance from the rest of the resonant circuit and connected thereto by coaxial cables 18. The plates of the capacitor may be concave arched in shape which surround the material as it passes therethrough, one of the plates being earthed and the other spring-biased towards the material Fig. 1, (not shown). Alternatively the plates may be planar Fig. 2 (not shown), or in the form of running rollers or bands Fig. 3 (not shown).