Single frequency moisture gauge with two-channel demodulation and feedback control of input

Claim 1

Apparatus for the quantitative determination of a property of a dielectric material, said apparatus comprising a source of alternating current electrical signal at a constant frequency, said source including control means responsive to a control signal for controlling the magnitude of said signal from said source, detecting means, capacitance probe means coupled to said source and having spaced electrodes arranged for applying said electrical signal from said source to at least a portion of said material and coupling said detecting means to said portion, said detecting means including means for deriving a detection signal resulting from the signal as applied to said portion from said source as this applied signal is influenced by said material, balancing circuit means connected in circuit with said probe means to balance out from said detection signal any component developed by said probe means in the absence of said material, a signal converter coupled to said detecting means and responsive to said detection signal by producing a derived signal monotonically related to said detection signal over the range of measurement, means for applying said derived signal to said control means as a control signal to change the magnitude of said signal from said source oppositely from any change in the magnitude of said detection signal, and ratio-taking means coupled to said signal converter and said source and responsive to said derived signal and said signal from said source to producE a signal systematically related to the ratio of said derived signal and said signal from said source and hence indicative of said property.

Claim 7

A method for the quantitative determination of a property of a dielectric material, said method comprising applying a constant frequency alternating current electrical signal of controlled magnitude to a pair of spaced electrodes of a capacitance probe, deriving a detection signal resulting from the applied signal as this applied signal is influenced by said material while at the same time balancing out from said output signal any effect of the capacitance between said electrodes in the absence of said material, deriving from said detection signal a derived signal monotonically related thereto over the range of measurement, utilizing said derived signal to control the magnitude of said applied signal by changing said magnitude oppositely to any change in said detection signal, and combining said derived signal and a signal indicative of said applied signal to produce a signal systematically related to the ratio of said detection signal and said applied signal and hence indicative of said property.

Claim 8

A method for the quantitative determination of a property of a dielectric material, said method comprising applying a constant frequency alternating current electrical signal of controlled magnitude to a pair of spaced electrodes of a capacitance probe, deriving a detection signal resulting from the applied signal as this applied signal is influenced by said material while at the same time balancing out from said output signal any effect of the capacitance between said electrodes in the absence of said material, deriving from said detection signal a derived signal monotonically related thereto over the range of measurement, utilizing said derived signal to control the magnitude of said applied signal by changing said magnitude oppositely to any change in said detection signal, and combining said derived signal and a signal indicative of said applied signal to produce a signal systematically related to the ratio of said detection signal and said applied signal and hence indicative of said property.