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Liquid transfer device for an analysis unit

  • US 5,304,347 A
  • Filed: 02/05/1993
  • Issued: 04/19/1994
  • Est. Priority Date: 02/08/1992
  • Status: Expired due to Term
First Claim
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1. A liquid transfer device for an analysis unit, the liquid transfer device comprising:

  • a liquid transfer needle having a tip;

    a capacitive liquid level detector for detecting a dipping of the tip of the liquid transfer needle into an analysis liquid, the analysis liquid being contained in a vessel, said capacitive liquid level detector comprisinga coaxial electrode arrangement including said liquid transfer needle and a first coaxial electrode coaxially surrounding said liquid transfer needle with the exception of the tip which projects therefrom, said first coaxial electrode being electrically insulated from said liquid transfer needle, wherein said liquid transfer needle and said first coaxial electrode of said coaxial electrode arrangement are coupled to a detection circuit comprising isolation amplifier circuit means for producing an output signal which corresponds to the input signal in phase and level, wherein an output side internal resistance of said isolation amplifier circuit means is lower than an input resistance thereof;

    said liquid level detector further comprisingan a.c. voltage source connected to an input of said isolation amplifier circuit means and one of said first coaxial electrode and said liquid transfer needle, said one of the liquid transfer needle and said coaxial electrode forming a signal electrode,wherein the other of said liquid transfer needle and said first coaxial electrode is coupled to an output of said isolation amplifier circuit means and forms a compensating electrode.

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