Magnetic-field-responsive proximity detector apparatus

Claim 1

A magnetic-field-responsive proximity detector apparatus comprising A. a magnetic-field-sensing probe having a magnetic-fieldsensing device positionable in magnetically coupled relationship to an environmental magnetic field for responding thereto in forming a probe output voltage signal related to the magnitude of the magnetic field sensed, said environmental magnetic field having a normal quiescent state subject to distortion by ferromagnetic objects which results in an increase in said probe output voltage signal relative to a normal quiescent level, B. an output circuit having first and second operating states providing associated output signals, said output circuit normally being in said first operating state and switchable to said second operating state in response to receipt of a control signal, and C. a control circuit connected to said probe and said output circuit and providing said control signal for switching said output circuit between said first and second operating states in response to said probe output voltage signal, said control circuit including a voltage-level-sensing circuit having an input responding to an increase of at least a predetermined magnitude in said probe output voltage signal to provide said control signal for switching said output circuit to the second of said two operating states, said voltage-level-sensing circuit including a switching device connected to a voltage source and having an output terminal providing a relatively high voltage when said device is nonconducting and a relatively low voltage when said device is conducting, and a voltagelevel-regulating circuit including a regulated voltage source, a first feedback circuit connected between said switching device output terminal, said regulated voltage source and said level-sensing circuit input for regulating the voltage at said input at a normal quiescent level only when the increase in input voltage is less than a predetermined magnitude above said quiescent level, and a second feedback circuit connected between said switching device output and said voltage-levelsensing circuit input for regulating the voltage at said input at a level greater than a normal quiescent level after lapse of a predetermined time interval subsequent to switch of said output circuit to said second operating state, said second feedback circuit responding to a subsequent increase in the voltage at said input greater than said predetermined magnitude to return control of voltage-level-regulating to said first feedback circuit when the voltage at said input decreases an amount at least equal to said predetermined magnitude and switching said output circuit to said first operating state.