Measuring and testing – Fluid pressure gauge – Null balance type
Patent
1984-04-02
1985-10-15
Ciarlante, Anthony V.
Measuring and testing
Fluid pressure gauge
Null balance type
331 65, G01L 912
Patent
active
045466513
ABSTRACT:
A circuit for coupling a transducer having a reactive sensing element to equipment providing either AC or DC drive voltage and equipped with strain gauge amplifiers in which the sensing impedance varies the gain of the feedback loop of an oscillator, an AGC circuit is coupled to the loop so as to derive a control signal related to the amplitude of oscillations therein and a gain control means is included in the loop that responds to the control signal in such manner as to restore the loop gain to unity after it has been changed therefrom by changes in the value of the sensing impedance. If the gain control means is a voltage divider having a variable resistor as the operative element, a matched variable resistor is used as the unbalancing element of a resistive bridge, and the values of the circuit are chosen such that the output signal from the bridge which may be applied to strain gauge amplifiers is linearly or desirably nonlinearly related to changes in the value of the reactive sensing impedance. Operating potentials for the oscillator are derived by a rectifier from the drive voltage. If the control signals is to be used as a linear output signal, the variable resistor of the voltage divider is made to have a suitably nonlinear relation with respect to the value of the control signal. The variable resistor can be a nonlinear digitally controlled resistor in which event the control signal can be digitized without using an A/D converter.
REFERENCES:
patent: 4434664 (1984-03-01), Antonazzi
patent: 4449409 (1984-05-01), Antonazzi
Ciarlante Anthony V.
Hewlett-Packard Co.
Timbie Donald N.
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