Abstract: A moisture analyzing system including an antenna coupled to a frequency-modulated voltage source and arranged to apply an alternating electric field to a material being tested for moisture content. An LC tank circuit is connected in parallel with the antenna and a resistance is connected between the source and the parallel combination of the antenna and the tank circuit. Detecting the level of resonant voltage peak output signals produced across the tank circuit is a measurement circuit which provides therewith a sensing signal indicative of the moisture content of the material being tested. The detection of resonant peak amplitudes produced by frequency sweeping a tank circuit eliminates many unstable variables that interfere with moisture measurements.

Abstract: Apparatus for measuring moisture content of gypsum board and like products as a function of dielectric constant comprising an rf signal source, an antenna disposed for rf field coupling to a test material, first and second reference inpedances, and a control circuit for selectively connecting the reference and antenna impedances to the output of the rf source. A rectifier is responsive to source output for providing the corresponding d.c. signal to measurement electronics. The measurement electronics first subtract a first reference signal indicative of the reference impedances from both a differing second reference signal indicative of the reference impedances and from a signal indicative of impedance at the antenna. Moisture content is then determined as a function of the ratio of the differences. A threshold detector is responsive to the difference between the antenna and reference signals for indicating the presence of test material adjacent the antenna.