Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1994-01-13
1995-06-13
Regan, Maura K.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324690, 137 785, G01R 2726
Patent
active
054246490
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.
REFERENCES:
patent: 4137931 (1979-02-01), Hasenbeck
patent: 4850386 (1989-07-01), Bireley
patent: 4952868 (1990-08-01), Schrer, III
patent: 4989628 (1991-02-01), Gil et al.
patent: 4993640 (1991-02-01), Baugh
Feniger Naftali
Friedman Anatoly
Gluck Israel
Langer Edward
Regan Maura K.
Silora Television & Electronics
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