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Liquid level sensor

  • US 4,056,979 A
  • Filed: 10/31/1975
  • Issued: 11/08/1977
  • Est. Priority Date: 10/31/1975
  • Status: Expired due to Term
First Claim
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1. A liquid level sensor comprising, in combination:

  • a guide tube for vertical positioning in the liquid whose level is to be sensed;

    a float externally surrounding the guide tube for free rotatable and longitudinal movement thereon to rise and fall with the liquid level;

    a reed switch in the guide tube having its reeds extending substantially parallel to the axis of the guide tube;

    means for establishing a magnetic bias field across the reeds insufficient to close them but sufficient to hold them closed;

    means on the float for establishing a symmetrical toroidal magnetic field about the guide tube having leading and trailing field portions of opposite direction for sweeping the switch reeds and augmenting the bias field to close the reeds as the float passes the switch moving in one direction and sweeping and overcoming the bias field opening the switch reeds as the float passes the switch moving in the opposite direction at substantially the same point where the reeds were closed.

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