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TELEMETERING TRANSDUCER CIRCUITRY FOR CONVERTING A CAPACITANCE SIGNAL TO A DC CURRENT SIGNAL

  • US 3,646,538 A
  • Filed: 10/27/1969
  • Issued: 02/29/1972
  • Est. Priority Date: 10/27/1969
  • Status: Expired due to Term
First Claim
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1. A two-wire current transmitter for providing a direct current signal proportional to a condition to be measured comprising a pair of excitation terminals for connection to direct current supply means, an AC reactive impedance means which varies as a function of the condition to be measured, an oscillator means energized by current drawn through the excitation terminals and having its output coupled to the AC impedance means for applying an alternating current therethrough, current rectification means in circuit with the oscillator and AC impedance means to provide a first DC voltage signal representative of the magnitude of the AC impedance, a reference DC means which provides a second DC voltage signal independent of the variable AC impedance, a current control amplifier means having input signal terminals and providing an output control signal in response to a signal at its input terminals and which is energized by current drawn through the excitation terminals, current control means connected between the excitation terminals and controlling the current drawn therethrough in response to the control signal, a first network means, including means summing the total direct current drawn through the excitation terminals, for arithmetic comparison of the first and second voltage signals and the total direct current, and means connecting the network means to the amplifier input signal terminals so that a control signal is produced which adjusts the current through the control means to provide a prescribed relation between total direct current and the condition to be measured.

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