Soil moisture sensor
First Claim
1. A method of sensing the moisture content of a volume of a medium, the medium having a dielectric constant dependant on the medium'"'"'s moisture content, the method comprising the steps of:
- disposing first and second spaced apart conductive sensor elements within said volume of the medium, to provide a capacitance dependent upon the dielectric constant of the medium when disposed within said volume of the medium;
coupling an inductance element to said first and second sensor elements in an LC oscillator circuit having an oscillation frequency dependent on the values of the inductance element and the capacitance value provided by the first and second sensor elements disposed in the medium; and
outputting a moisture content indicative output signal as a function of the oscillation frequency of the LC oscillator circuit.
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Accused Products
Abstract
Moisture sensor devices, systems and methods of making and using the same employ a pair of elongated, probe-like, conductive sensor elements, coupled as part of an LC oscillator circuit. The use of an LC oscillator circuit can minimize adverse effects of conductivity variances in the medium being monitored, because the resistance of the medium (and, thus, the medium'"'"'s conductivity) has minimal or no effect on the resonant frequency of an LC oscillator circuit. An LC oscillator circuit of suitable stability for moisture sensing applications includes first and second comparators connected such that the output of the first comparator is coupled to the inverting input of the second comparator. An inductor is coupled between the output and inverting input of the first comparator and a capacitance C is provided between the output of the second comparator and the inverting input of the first comparator. The capacitance C is composed primarily of the capacitance value provided by the pair of probe-like sensor elements and the dielectric constant of the medium in which the probe-like sensor elements are disposed. The capacitance is averaged over the length of the probe-like sensor elements.
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Citations
28 Claims
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1. A method of sensing the moisture content of a volume of a medium, the medium having a dielectric constant dependant on the medium'"'"'s moisture content, the method comprising the steps of:
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disposing first and second spaced apart conductive sensor elements within said volume of the medium, to provide a capacitance dependent upon the dielectric constant of the medium when disposed within said volume of the medium; coupling an inductance element to said first and second sensor elements in an LC oscillator circuit having an oscillation frequency dependent on the values of the inductance element and the capacitance value provided by the first and second sensor elements disposed in the medium; and outputting a moisture content indicative output signal as a function of the oscillation frequency of the LC oscillator circuit. - View Dependent Claims (2, 3, 19, 20, 25, 26, 27)
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4. A method of sensing the moisture content of a volume of a medium, the medium having a dielectric constant dependant on the medium'"'"'s moisture content, the method comprising:
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inducing oscillation in an LC oscillator circuit having an oscillation frequency dependent on the values of an inductance element and a capacitance element, the capacitance element comprising first and second spaced apart conductive sensor elements disposed within said volume of the medium, wherein the capacitance value provided by the first and second sensor elements is dependent upon the dielectric constant of the medium when the sensor elements are disposed within said volume of the medium; and outputting a moisture content indicative output signal as a function of the oscillation frequency of the LC oscillator circuit.
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5. A moisture sensor device for sensing the moisture content of a volume of a medium, the medium having a dielectric constant dependant on the medium'"'"'s moisture content, the device comprising:
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an LC oscillator circuit having an inductance element and a capacitance element and an oscillation frequency dependent on the values of the inductance and capacitance elements; wherein the capacitance element comprises first and second spaced apart conductive sensor elements configured to be disposed within said volume of the medium, to provide a capacitance dependent upon the dielectric constant of the medium when disposed within said volume of the medium; and an output circuit for providing a moisture content indicative output signal as a function of the oscillation frequency of the LC oscillator circuit. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22)
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23. A moisture sensor system for sensing the moisture content of a medium, the medium having a dielectric constant dependant on the medium'"'"'s moisture content, the system comprising:
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at least one moisture sensor device having an LC oscillator circuit provided with an inductance element, a capacitance element and an oscillation frequency dependent on the values of the inductance and capacitance elements, wherein the capacitance element comprises first and second spaced apart conductive sensor elements configured to be disposed within said volume of the medium, to provide a capacitance dependent upon the dielectric constant of the medium when disposed within said volume of the medium; an output circuit for providing a moisture content indicative output signal as a function of the oscillation frequency of the LC oscillator circuit; and a central processing unit for monitoring the output signal of the at least one moisture sensor. - View Dependent Claims (24)
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28. A moisture and conductivity sensor device for sensing the moisture content and conductivity of a volume of a medium, the medium having a dielectric constant dependant on the medium'"'"'s moisture content and a conductivity dependent on the medium'"'"'s moisture content and the concentration of conductive material in the medium, the device comprising:
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an LC oscillator circuit having an inductance element and a capacitance element and an oscillation frequency dependent on the values of the inductance and capacitance elements; wherein the capacitance element comprises first and second spaced apart conductive sensor elements configured to be disposed within said volume of the medium, to provide a capacitance dependent upon the dielectric constant of the medium when disposed within said volume of the medium; a conductivity sensor for sensing the conductivity of the medium with said volume; means responsive to the sensed conductivity of the medium within said volume and further responsive to the oscillation frequency of the LC oscillator circuit, for providing a signal representative of the component of the sensed conductivity contributed by the concentration of conductive material in said volume of the medium.
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Specification