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Electromagnet weighing balance

  • US 3,968,850 A
  • Filed: 10/31/1974
  • Issued: 07/13/1976
  • Est. Priority Date: 10/31/1974
  • Status: Expired due to Term
First Claim
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1. In an electromagnetic weighing balance including a movable support system for a mass to be weighed, said support system including an electromagnetic balance coil disposed in the field of a permanent magnet, sensor means responsive to displacement of said support system from a datum position to develop a control signal representative of said displacement, a signal-controlled current source feeding to said balance coil a balancing current producing on said support system a force balancing said mass, balance circuit means fed with said control signal and applying a balancing signal derived therefrom to control said current source, and indicator means responsive to said balancing current to provide a measure of said mass, the improvement which comprises constructing said current source as a high impedance source comprising a transistor (45) having emitter, base and collector electrodes, with said balance coil connected between the collector electrode of said transistor and one terminal of a direct voltage source and the emitter electrode of the transistor returned to the other terminal of said voltage source, and means applying said balancing signal to said transistor base electrode, thereby to control the balancing current supplied to said balance coil.

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