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Rain sensor with variable shut off

  • US 8,744,773 B2
  • Filed: 05/19/2010
  • Issued: 06/03/2014
  • Est. Priority Date: 05/19/2010
  • Status: Active Grant
First Claim
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1. A rain sensor comprising:

  • at least one hygroscopic member;

    an electronic sensor that detects an amount of expansion of the hygroscopic member upon absorbing moisture;

    a computer processor; and

    a memory connected to the computer processor and pre-programmed with an algorithm that enables the computer processor to determine the presence of rainfall and generate a shut off command, the determination being based on the signals generated by the electronic sensor indicating that the at least one hygroscopic member has expanded a predetermined amount and has expanded at a predetermined rate;

    wherein the algorithm causes the computer processor to periodically calculate a dry-to-wet threshold and a wet-to-dry threshold, to periodically determine minimum and maximum set points for a range of travel of a magnet operatively coupled to the at least one hygroscopic member, and to generate the shut off command when the magnet has moved a predetermined percentage away from the minimum set point.

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