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Fluid level detector using thermoresistive sensor

  • US 6,098,457 A
  • Filed: 01/18/1999
  • Issued: 08/08/2000
  • Est. Priority Date: 01/18/1999
  • Status: Expired due to Term
First Claim
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1. A fluid level detector for being immersed in a fluid and thereby determining the fluid level, comprising:

  • a) a substrate formed of a heat-insulative material;

    b) at least one thermoresistive sensor element located on the substrate to form a, having a resistivity that changes substantially linearly in response to temperature change;

    c) a current source, connected to the sensor element, for producing a current Through the sensor element for a predetermined time period to thereby heat the sensor element during the predetermined time period, the current source producing a voltage across the sensor element at least during the predetermined time period;

    d) means for measuring the voltage across the sensor element during the predetermined time period and for determining a voltage slope that varies relative to the amount of the sensor element that is immersed in the fluid;

    and means for monitoring the voltage across the sensor element subsequent to the predetermined time period for determining a stable condition of the sensor element.

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