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Liquid level sensor

  • US 4,736,638 A
  • Filed: 08/19/1987
  • Issued: 04/12/1988
  • Est. Priority Date: 12/20/1985
  • Status: Expired due to Term
First Claim
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1. Apparatus for detecting physical contact between a conductive probe and an exposed surface of one of a plurality of liquid samples held in sample containers, the apparatus comprising:

  • (a) an oscillator including means for generating an alternating current signal;

    (b) a stationary capacitive coupling member;

    (c) means for coupling the alternating current signal to the stationary capacitive coupling member;

    (d) a conductive member supporting the containers and disposed proximate the stationary capacitive coupling member whereby the alternating current signal is coupled to the conductive member and the conductive member couples the alternating current signal to all of the liquid samples supported by the conductive member;

    (e) conductive member support and drive means for moveably supporting the conductive member and moving the conductive member and the containers disposed on the conductive member with respect to the stationary capacitive coupling member;

    (f) amplifier means coupled to the probe for amplifying a signal received by the probe, the signal received by the probe including a signal produced by the alternating current signal; and

    (g) means responsive to the amplifier means for detecting a threshold level of the alternating current signal received by the probe indicative of contact between the probe and one of the liquid samples.

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