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US 5,418,466 AGranted
Moisture and salinity sensor and method of use
OwnerKeith Watson, Rick Gatto +2inventors
InventorsKeith Watson, Rick Gatto, Peter Weir, Peter Buss
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Abstract
The invention relates to a moisture and salinity measurement and in particular to a sensor and its method or use which may provide values for the moisture/complex dielectric constant of a variety of mediums. A sensor apparatus is arranged for indicating the complex dielectric constant and conductivity of a medium and uses a tuned circuit. The tuned circuit oscillates such that the frequency of oscillation is representative of the complex dielectric constant of the medium.
Claims7
A sensor apparatus for indicating the complex dielectric constant and conductivity of a medium comprising
- oscillator means including a tuned circuit having a complex impedance means wherein a value of the complex impedance means is established by the variable complex dielectric constant of said medium,
- said tuned circuit further comprising a variable impedance means having a first impedance value and a second impedance value for resonating with said complex impedance means respectively at a first frequency and at a second frequency less than said first frequency,
- said oscillator means including means for selecting said first or said second impedance value, a value of said first frequency and a value of said second frequency being dependent on the complex dielectric constant of said medium,
- wherein said selecting means is operative to select said first and said second impedance values sequentially to operate said oscillator means to output said first and said second frequencies sequentially,
- in a first mode of operation of said oscillator means, the first oscillator frequency is representative of a first value of the complex dielectric constant of the medium,
- in a second mode of operation of said oscillator means, the second oscillator frequency is representative of a second value of the complex dielectric constant of the medium, and
- said sensor apparatus further comprises means for obtaining a difference between said first frequency and said second frequency, the difference between an oscillator frequency of the first mode and an oscillator frequency of the second mode being representative of the conductivity of the medium.
4 more elements
A method of determining the conductivity of a medium comprising the steps of:
- (a) placing a sensor apparatus in a medium where said sensor comprises
- an oscillator means comprising a tuned circuit having a variable complex impedance means influenced by the variable complex dielectric constant of said medium where oscillator frequency is representative of the complex dielectric constant of the medium,
- a control circuit connected to said variable complex impedance for controlling said oscillator means into a first mode of operation in which the variable complex impedance means is varied such that the oscillator frequency is representative of a first complex dielectric constant of the medium and also representative of the moisture content of the medium, and further the control circuit controls the oscillator means into a second mode of operation in which the variable complex impedance means is varied such that the oscillator frequency is representative of a second complex dielectric constant of the medium and also representative of the moisture content and conductivity of the medium, wherein the difference between an oscillator frequency of the first mode and an oscillator frequency of the second mode is representative of the conductivity of the medium,
- (b) controlling said control circuit to operate in said first mode and recording on a recording means a representation of said oscillator frequency,
- (c) controlling said control circuit to operate in said second mode and recording on a recording means a representation of said oscillator frequency,
- (d) determining with a computer means according to a calibration equation using the representation of said oscillator frequency from said first mode of operation of said sensor apparatus the moisture content of said medium,
- (e) determining with said computer means according to said calibration equation using the representation of said oscillator frequency from said second mode of operation of said sensor apparatus the absolute combined moisture content and conductivity of said medium as volumetric soil water content,
- (f) determining with said computer means the difference between said first mode and second mode volumetric soil water content, wherein said difference is representative of the conductivity of the medium.
5 more elements
Dependencies are inferred from the claim text.