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Position Sensor

IP.com Disclosure Number: IPCOM000074175D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Melnyk, G: AUTHOR

Abstract

A sensing circuit utilizes spaced apart ferrite cores 10 and 12 having windings L1 and L2 thereon which provide with a capacitor C1 and transistors T1 and T2 an oscillator. With no conducting material in the gap between 10 and 12 the voltage at A will swing above and below ground as the circuit oscillates. The negative portion of the cycle is conducted through diodes D1 and D2 to the base of T3 which with T4 forms a latch. T3 is turned off, causing T4 to turn on. With the collector of T4 at ground, C3 will hold point B negative between oscillator cycles.

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Position Sensor

A sensing circuit utilizes spaced apart ferrite cores 10 and 12 having windings L1 and L2 thereon which provide with a capacitor C1 and transistors T1 and T2 an oscillator. With no conducting material in the gap between 10 and 12 the voltage at A will swing above and below ground as the circuit oscillates. The negative portion of the cycle is conducted through diodes D1 and D2 to the base of T3 which with T4 forms a latch. T3 is turned off, causing T4 to turn on. With the collector of T4 at ground, C3 will hold point B negative between oscillator cycles.

If a metal vane V (brass, for example) is moved into the gap between 10 and 12, the amplitude of oscillations at A will drop. R4 will now turn on T3 which turns off T4. The collector of T4 going positive drives the base of T3 more positive through C3 and R7. Since the base of T3 is now forward biased, D1 and D2 appear across L2, lowering the impedance across it and causing the oscillator output to drop still further. When the vane is removed, the circuit returns to its original state. This arrangement has a clean output with fast rise and fall times because of the latch. The response of the circuit is good as there is a minimum of filtering required for the rectified oscillator output.

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