Soil moisture sensor
First Claim
1. A soil moisture sensor comprising:
- at least a pair of rod-shaped electrodes being spaced apart from one another by a relatively large distance in relation to their diameters, each of said electrodes being disposed in the earth and having a thin dielectric coating each said electrode defining a first plate of a capacitor, said thin dielectric coating being in contact over an area thereof with a plurality of soil particles containing moisture to define a second plate of each of said capacitors over said contact area, said pair of electrodes each providing a capacitor having a relatively high capacitance, said pair of capacitors being connected serially through conductivity of said soil particles containing moisture, andvariable frequency oscillator means coupled to said capacitors and providing an output frequency responsive to a sensed capacitance,wherein said sensed capacitance is related to an effective conducting area defined by said contact area between said thin dielectric coating and said moisture contained by said plurality of soil particles.
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Accused Products
Abstract
A soil moisture sensor using sensor electrodes each designed with a larger capacitance for reduced sensitivity to soil resistance and increased sensitivity to soil moisture surrounding the electrode. The soil moisture sensor is provided as a pair of cylindrical rods each coated with a thin layer of dielectric material, which are buried in the soil or other medium and are connected to a conversion circuit in which the electrodes act as a variable capacitance. The capacitance developed by each of the sensor electrodes is related to the moisture contained in the soil particles surrounding the electrodes. An effective conducting area is developed by the soil particles in contact with the electrodes and this determines the value of the variable capacitance presented to the conversion circuit. The conversion circuit is a multivibrator in which the variable capacitance determines the output frequency, and this provides a measurement of soil moisture. Alternatively, the conversion circuit provides the measurement as a voltage output. The use of a relatively thin dielectric coating on each of the electrodes increases the capacitance and reduces the soil resistance as a factor in the soil moisture measurement. Based on the cylindrical shape of the sensor electrodes and dielectric coating, a linear relationship is developed between capacitance and the electrode length in contact with soil particles containing moisture, which increases the accuracy of soil moisture measurement at soil depths of interest. The inventive soil moisture sensor can be used to control valves in automatically-controlled irrigation systems.
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Citations
18 Claims
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1. A soil moisture sensor comprising:
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at least a pair of rod-shaped electrodes being spaced apart from one another by a relatively large distance in relation to their diameters, each of said electrodes being disposed in the earth and having a thin dielectric coating each said electrode defining a first plate of a capacitor, said thin dielectric coating being in contact over an area thereof with a plurality of soil particles containing moisture to define a second plate of each of said capacitors over said contact area, said pair of electrodes each providing a capacitor having a relatively high capacitance, said pair of capacitors being connected serially through conductivity of said soil particles containing moisture, and variable frequency oscillator means coupled to said capacitors and providing an output frequency responsive to a sensed capacitance, wherein said sensed capacitance is related to an effective conducting area defined by said contact area between said thin dielectric coating and said moisture contained by said plurality of soil particles. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of measuring soil moisture comprising the steps of:
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providing at least a pair of rod-shaped electrodes, being spaced apart from each other by a relatively large distance in relation to their diameters, each of said electrodes being disposed in the earth and having a thin dielectric coating, each said electrode defining a first plate of a capacitor, said thin dielectric coating being in contact over an area thereof with a plurality of soil particles containing moisture to define a second plate of each of said capacitors over said contact area, said pair of electrodes each providing a capacitor having a relatively high capacitance, said pair of capacitors being connected serially through conductivity of said soil particles containing moisture; sensing a capacitance developed between said first plate and said contact area of each electrode; and providing an output frequency responsive to said sensed capacitance, wherein said sensed capacitance is related to an effective conducting area defined by said contact area between said thin dielectric coating, and said moisture contained by said plurality of soil particles. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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Specification