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Moisture sensing electronic irrigation control

  • US 5,749,521 A
  • Filed: 05/22/1996
  • Issued: 05/12/1998
  • Est. Priority Date: 05/22/1996
  • Status: Expired due to Fees
First Claim
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1. An apparatus for comparing the amount of moisture in soil with a reference setting and controlling the application of irrigation water, comprising:

  • an electronic means for generating periodic electrical current pulses that pass through the soil between two conductive electrodes fixed upon a nonconductive support and disposed beneath the surface of the soil, said electrical current being in the form of a unipolar pulse of the briefest practical duration followed immediately by a unipolar pulse of the same duration and current amplitude having opposite polarity,an electronic comparator means that compares the voltage potential difference produced by said electrical current pulses between said conductive electrodes with a voltage potential expressing a reference setting,an electronic sensor means for measuring temperature of the air or soil and applying a correction to said voltage potential that expresses said reference setting, equal to the effect from change with temperature of the apparent electrical resistance in the soil medium,an electronic switching means that completes an electrical circuit for electrically controlled irrigation valves when the voltage potential difference produced by said electrical current between said conductive electrodes exceeds said voltage potential expressing the reference setting,and an electronic means that detects the presence of an external control signal and that causes cessation of said periodic electrical current pulses during the presence of said external control signal.

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