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Signal amplifier system for controlled carrier signal measuring sensor/transducer of the variable impedance type

  • US 4,176,555 A
  • Filed: 08/07/1978
  • Issued: 12/04/1979
  • Est. Priority Date: 08/07/1978
  • Status: Expired due to Term
First Claim
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1. A controlled carrier circuit measuring sensor/transducer signal amplifier system including in combination a carrier signal oscillator for providing a carrier oscillatory signal of known frequency and fixed voltage magnitude, differential amplifier means having the carrier oscillatory signal supplied to one of the inputs thereof, reference impedance means and variable impedance sensor/transducer means connected in series circuit relationship across the output of said differential amplifier means, means for feeding back a first feedback signal to a second input to said differential amplifier means, said first feedback signal comprising the sum of the voltages across said reference impedance means and said variable impedance sensor/transducer means in series, buffer amplifier means having the input thereof connected to the juncture of the reference impedance means and the variable impedance sensor/transducer means for deriving an output voltage signal representative of the instantaneous value of the voltage across said variable impedance sensor/transducer means, and means for feeding back said output voltage signal from the output of said buffer amplifier means to a third input to said differential amplifier means in opposition to said first feedback signal for regulating the current supplied through said reference impedance means and said variable impedance sensor/transducer means to a substantially constant magnitude whereby the output voltage signal from said buffer amplifier means provides a measure of the impedance of said variable impedance transducer means.

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