Method for measuring the material moisture content of a material under test using microwaves

A method for measuring the moisture content of a material under test using microwaves, in which method, under the control of a processor, an electromagnetic radiation of variable frequency is generated in a microwave generator and is fed to a sample applicator designed as a resonator, and in which the microwave signal emerging from the applicator is fed to a detector diode, from which signals b(O) and f(O) are determined as primary process variables by a computer via an analog/digital converter, where b(O) is the resonance half-width value at the resonance frequency f(O) of the applicator which is operatively connected to a test sample, whereby

• a material sample is brought into connection with the resonator so that an electric field extends generally parallel to the sample, and
• a null compensation for the detector diode is undertaken outside the resonance frequency f(O),
• the method further comprising the steps of calibration comprising the evaluation of samples of various material with known moisture content values .PSI.r, using a measurement signal .PHI.(.PSI.r) calculated as:
• ##EQU3## with b(L) and f(L) as constant material-dependent and applicator dependent reference quantities which are determined in accordance with the relations
• b(L)=b(LO)+B
• f(L)=f(LO)+F
• in which b(LO) and f(L0) are the half-width value and the resonance frequency respectively of the applicator without material under test and B and F are stored constants which are typical for the applicator and which are determined in a manner dependent upon the material to be measured, so that the measurement signal .PHI.(.PSI.r) is independent of the packing density of the material and is dependent only upon the moisture content, and wherein disturbing influences of resonator contaminations and resonator temperature alterations are compensated by measurement and storage of b(LO) and f(LO) and recomputation of the measurement signal .PHI.(.PSI.r).