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Sensor Circuit Utilizing Variable Inductance Input

IP.com Disclosure Number: IPCOM000075444D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 27K

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 12 may be used to control the characteristic of the material. Coil 10 and capacitor 14 are coupled across one arm of a bridge circuit 16. The bridge circuit is energized by a constant-amplitude constant- frequency output from oscillator 18. With the material at a reference point, the bridge is adjusted to a balance with resistor 20 after coil 10 and capacitor 14 have been adjusted for resonance at the frequency of oscillator 18. This constitutes an initial normalization of the system and under these conditions no signals appear at output terminals 12, 12'. As the characteristic of the material flowing through the system changes, the inductance varies and this results in detuning the parallel resonant LC circuit. The impedance of the LC circuit also changes and causes the bridge to unbalance. The unbalanced signal is amplified by differential amplifier 22, rectified by diode 24 and filtered by the network comprised of resistor 26 and capacitor 28 to produce a DC output signal. A buffer amplifier 30 is utilized to provide a high-input impedance to the network and to present low-output impedance to the control circuits.

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