| 摘要 |
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. This voltage is then introduced to a comparator. A second voltage obtained from the voltage source and adjustable to indicate a desired amount of moisture in the monitored area of earth is also introduced to the comparator. The comparator produces an output dependent upon the relative values of the direct voltage obtained from the variable frequency signal and the adjustable direct voltage. This output controls the energizing of a solenoid at that position. When the solenoid is energized, it operates the valve for producing a watering of the patch of earth.
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