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Browse Prior Art Database

Sensor Circuit Utilizing Variable Inductance Input

IP.com Disclosure Number: IPCOM000075448D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Ogren, VG: AUTHOR

Abstract

A circuit for sensing changes in inductance of inductive coil 10 is shown.

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Sensor Circuit Utilizing Variable Inductance Input

A circuit for sensing changes in inductance of inductive coil 10 is shown.

For example, a characteristic of a material flowing through coil 10 can be sensed by sensing the resultant change in inductance of coil 10, and the signal generated at the output terminal 18 may be used to control the characteristic of the material. The inductance coil 10 and capacitor 14 are connected to the input of a variable-frequency oscillator 12. When the material characteristic changes, the inductance of coil 10 changes causing the oscillator 12 frequency to vary. A phase-locked loop is provided which operates essentially as an FM demodulator. A voltage-controlled oscillator 16 is provided and the output of oscillator 12 is phase compared with oscillator 16 in phase comparator 20. As the frequency of oscillator 12 changes, the internally generated DC control signal changes in a linear fashion, thereby adjusting the frequency of oscillator 16 to the same frequency. Potentiometer 22 is a DC offset control which can be used to normalize the DC output level. An output signal is provided at terminal 18 for closed-loop control over the sensed characteristic of the material. The part of the circuit enclosed in dotted lines can conveniently be constructed as a linear- integrated circuit.

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