Abstract: A capacitive moisture sensor has two conductors encased in a dielectric material and oriented to minimize the dielectric effect of the moisture-absorbent medium in which the sensor is placed. The conductors, the casing, or both have one or more physical dimensions that vary monotonically across the length of the sensor. The physical dimensions vary in a manner that produces a linear relationship between moisture level and sensor impedance. The physical dimension may be the thickness of the dielectric casing or the spacing between portions of the conductors. In another aspect, the present invention has an irrigation control system with a central control unit and multiple remote units. Each remote unit has a moisture sensor and transmits a measured moisture level to the central control unit. In response to the measured moisture level, the central control unit determines whether to open or close a valve controlling the irrigation of the area in which the sensor is located.

Abstract: A sensor is disposed in an earth patch for sensing the amount of moisture in such patch by providing a capacitance having a variable value dependent upon the sensed moisture. The variable capacitance is included in an oscillator which produces a signal at a frequency variable in accordance with variations in the capacitive value. The oscillator is energized by a direct potential passing through a cable from a potential source at a central station. A rectifier and a filter capacitor prevent the signal produced in the oscillator from interfering with the energizing of the oscillator by the direct potential. The signal from the oscillator passes through the cable to a stage at a controller. The incoming signal is prevented from interfering with the energizing voltage source by a filter inductor. A first controller stage reestablishes the incoming signals relative to a ground potential. The signal is the converted to a direct voltage which varies as a function of signal frequency.

Abstract: A includes a first capacitance plate, a dielectric covers a first capacitance plate, second capacitance plates are formed by moisture in an area. The capacitance value, dependent upon the second plate formation, controls the frequency of signals produced by an oscillator. This frequency controls the opening and closing of a first switch. A second switch is in a circuit with the first switch and a solenoid. The closing of the second switch is dependent upon the operation of circuitry energized by an alternating voltage. The alternating voltage is modified to extend the zero voltage level period which occurs at the zero cross-over in the negative direction. When this condition occurs, a pulse is generated by the detection circuitry and this pulse causes the second switch to remain closed. When the first switch operates to indicate no need to water the area, the solenoid is energized and an associated relay is opened.

Abstract: A monitor or sensor for sensing the moisture content of a surrounding medium comprises two electrodes connected in a detector circuit for detecting the impedance between them and producing an output signal proportional to the impedance. At least one of the electrodes is covered by a dielectric coating and the other electrode is positioned to minimize any capacitative effects between the electrodes through the surrounding medium. The detector may comprise a multivibrator with an output frequency controlled by the sensor impedance, and the output signal can be used to control the operation of watering equipment.

Abstract: A moisture sensor having an oscillator circuit with its output frequency directly proportional to moisture percentage present in the substance of interest. The oscillator circuit includes two spaced plates in the substance and functioning as a capacitor. The frequency of the oscillations changes as the capacitance between the plates changes due to the moisture present between the plates. The sensor is particularly adapted for use as a soil moisture detector and provides indications of wet or dry conditions.