The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 08, 1997
Filed:
Oct. 20, 1995
Wayne L Ehlers, Lanark, IL (US);
Honeywell Inc., Minneapolis, MN (US);
Abstract
A proximity sensor is provided with a means for sensing an attempt to tamper with the normal operation of a proximity sensor. An Eddy current killed oscillator is used to sense the presence of an undulating magnetic field provided by a coil and a monolithic timing circuit that periodically energizes and deenergizes the coil. A sensing coil is association with an Eddy current killed oscillator to provide an output signal that undulates in response to the undulations of the magnetic field provided by the stationary coil. If the output signal from the Eddy current killed oscillator changes states at a sufficient frequency to continually refresh a retriggerable resettable multivibrator, an output from the multivibrator will remain in a high condition and represent the coincident positions of the zones proximate the output coil and sensing coil. If, on the other hand, an attempt is made to tamper with the sensor by placing a metallic object near the sensing coil, the constant output from the Eddy current killed oscillator will fail to trigger the multivibrator at a sufficient frequency to maintain the high status of its Q output. In addition, the outputs from the Eddy current killed oscillator and the multivibrator are combined to determine that a tamper attempt has been made.