Browse Prior Art Database

Proximity Detector

IP.com Disclosure Number: IPCOM000073615D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Sensenbaugh, JD: AUTHOR

Abstract

The detector includes a coil 10 which is part of a parallel resonant circuit 12. The electrical properties of circuit 12 are changed by the proximity of a metal object 13 to coil 10 for indicating the proximity of object 13. The detector includes a current pulsing switch 14 represented by transistor T2; and when T2 is closed, a current from a current source representing T1 flows into resonant circuit 12. The form of the resulting voltage V-O is shown in A. The equivalent circuit is shown in FIG. B, and the equivalent resistance R varies as the distance of object 13 from coil 10 producing the variation in V-O. V-O is applied to a detector circuit 15 shown in FIG. E by lead 32. The integrator-rectifier 16 rectifies V-O and passes its negative-going portions integrating the result.

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Proximity Detector

The detector includes a coil 10 which is part of a parallel resonant circuit 12. The electrical properties of circuit 12 are changed by the proximity of a metal object 13 to coil 10 for indicating the proximity of object 13. The detector includes a current pulsing switch 14 represented by transistor T2; and when T2 is closed, a current from a current source representing T1 flows into resonant circuit
12. The form of the resulting voltage V-O is shown in A. The equivalent circuit is shown in FIG. B, and the equivalent resistance R varies as the distance of object 13 from coil 10 producing the variation in V-O. V-O is applied to a detector circuit 15 shown in FIG. E by lead 32. The integrator-rectifier 16 rectifies V-O and passes its negative-going portions integrating the result. The output voltage V-2 on lead 18 is shown in FIG. C. The reduced area under the negative half of the damped sinusoid when object 13 is near coil 10 results in the lower output voltage level B on lead 18. The output of integrator-rectifier 16 drives one input of a comparator circuit 20, and the second input to circuit 20 is derived by down- shifting the output of a threshold circuit 22 such that the signal on lead 24 lies approximately between levels A and B. Thus, the output on lead 26 from circuit 20 will be a 1 or a 0 depending on the presence or absence of object 13. The threshold level on lead 28 is established by closing charging switch 30 during the time that input 32 is arriving from a dummy coil 34 which is similar to coil 10 and is in a similar resonant circuit but has no metal object close to the coil. The output of integrator-rectifier 16 is stored at this time on a capacitor in circuit 22, and the outpu...