Magnetic detection means for sensing mobile ferromagnetic masses including pulse shaper circuit for generating a single pulse output
AssigneeU.S. Philips Corporation
InventorsYves Angel, Duc Mai Van Duc
Life of this patent
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Abstract
A device for detecting mobile ferromagnetic masses, notably of vehicles, comprising a magnetometric pick-up element of the type with orthogonal fields. The pick-up element is a ferrite tube of small dimensions which is provided with a toroidal pump winding and a solenoid signal winding. The output of the processing and amplifying device for the signal of the pick-up element is fed back to the solenoid winding via a circuit comprising a low-pass filter and a symmetrical current amplifier. A pulseshaper for the amplified signal supplied by the pick-up element comprises phase-shifting circuits, so that a single squarewave pulse can be obtained upon the passage of a metallic mass.
Claims14
A device for detecting mobile ferromagnetic masses along a path exposed to a permanent magnetic field comprising, a pick-up element for producing a signal indicating the local variations of said permanent magnetic field caused by the passage of said ferromagnetic masses, said pick-up element including an element which is made of a ferromagnetic material and which is provided with a pump winding and with a signal winding positioned orthogonal to the pump winding, means for supplying a current of a frequency f.sub.p to the pump winding so as to saturate the ferromagnetic material, a device for processing the signal supplied by the signal winding of the pick-up element comprising a cascade connection of a circuit for selecting an even harmonic of the frequency f.sub.p and a synchronous detector which provides a time varying output signal during passage of a ferromagnetic mass that constitutes the output signal of the processing device, a pulseshaper circuit responsive to said output signal for deriving a single pulse at its output upon the passage of each ferromagnetic mass, and a negative feedback circuit for coupling the output signal of the processing device to a solenoid winding of the pick-up element, and wherein the pulseshaper circuit includes phase-shifter means responsive to the output signal received from the synchronous detector for deriving at first and second terminals first and second voltages in phase opposition, first and second threshold level discriminators having first and second inputs coupled to said first and second terminals, respectively, each of said discriminators deriving at its output terminal voltage pulses of the same polarity but phase shifted relative to one another, and means for combining the voltage pulses at the output terminals of said first and second discriminators.
A system for detecting the movement of an object exhibiting ferromagnetic properties along a path exposed to a magnetic field comprising, magnetic field sensing means disposed adjacent said path and responsive to a variation of said magnetic field caused by the movement of said object, said sensing means comprising an element composed of a ferromagnetic material having a pump winding and a signal winding positioned orthogonally to one another, means for applying an alternating current to the pump winding of a magnitude to saturate the ferromagnetic element, means for processing the signal supplied by the signal winding of the sensing means to derive an output signal that varies with said supplied signal, said processing means including a frequency filter tuned to a even harmonic of the pump frequency, and a pulse-shaper network responsive to said alternating output signal and including phase-shift means for deriving first and second out of phase voltages determined by said alternating output signal, and means responsive to the first and second voltages for deriving pulse-shaped output signals of the same polarity whenever the respective first and second voltages exceed a given voltage level.
A device for detecting mobile ferromagnetic masses along a path exposed to a permanent magnetic field comprising, a pick-up element for producing a signal indicating the local variations of said permanent magnetic field caused by the passage of said ferromagnetic masses, said pick-up element including an element which is made of a ferromagnetic material and which is provided with a pump winding and with a signal winding positioned orthogonal to the pump winding, means for supplying a current of a frequency f.sub.p to the pump windng so as to saturate the ferromagnetic material, a device for processing the signal supplied by the signal winding of the pick-up element comprising a cascade connection of a circuit for selecting an even harmonic of the frequency f.sub.p and a synchronous detector which provides a time varying output signal during passage of a ferromagnetic mass that constitutes the output signal of the processing device a pulseshaper circuit responsive to said output signal for deriving a single pulse at its output upon the passage of each ferromagnetic mass, a negative feedback circuit for coupling the output signal of the processing device to the signal winding of the pick-up element, said feedback circuit comprising a low-pass filter and a symmetrical current amplifier, a limiting circuit, and wherein the pulseshaper circuit includes means for phase shifting the output signal received from the synchronous detector for deriving a plurality of voltages which are phase-shifted with respect to each other, means for applying said plurality of phase shifted voltages to respective inputs of a plurality of threshold-voltage discriminators, each discriminator including means for applying voltage pulses of the same polarity to the input of the limiting circuit.
A system for detecting the movement of an object exhibiting ferromagnetic properites along a path exposed to a magnetic field comprising, magnetic field sensing means disposed adjacent said path and responsive to a variation of said magnetic field caused by the movement of said object, said sensing means comprising an element composed of a ferromagnetic material having a pump winding and a signal winding positioned orthogonally to one another, means for applying an alternating current to the pump winding of a magnitude to saturate the ferromagnetic element, means for processing the signal supplied by the signal winding of the sensing means to derive an output signal that varies with said supplied signal, said processing means including a frequency filter tuned to an even harmonic of the pump frequency, means coupled to the output of the processing means and responsive to a variation in the output signal caused by movement of said object along said path for producing at its output a single pulse-type signal for each passing ferromagnetic object, and a negative feedback circuit coupling the output signal of the processing means to a solenoid winding of the field sensing means in a sense to counteract the signal voltage produced at said signal winding in the absence of a ferromagnetic object, and wherein said pulse-type signal producing means includes means responsive to said output signal for deriving first and second out of phase voltages, means responsive to said first and second voltages for producing first and second voltage pulses of the same polarity but phase shifted relative to one another, and means for combining said first and second voltage pulses to produce a single output pulse for each passing ferromagnetic object.
A device for detecting mobile ferromagnetic masses along a path exposed to a permanent magnetic field comprising, a pick-up element for producing a signal indicating the local variations of said permanent magnetic field caused by the passage of said ferromagnetic masses, said pick-up element including an element which is made of a ferromagnetic material and which is provided with a pump winding and with a signal winding positioned orthogonal to the pump winding, means for supplying a current of a frequency f.sub.p to the pump winding so as to saturate the ferromagnetic material, a device for processing the signal supplied by the signal winding of the pick-up element comprising a cascade connection of a circuit for selecting an even harmonic of the frequency f.sub.p and a synchronous detector which provides a time varying output signal during passage of a ferromagnetic mass that constitutes the output signal of the processing device, a pulseshaper circuit responsive to said output signal for deriving a single pulse at its output upon the passage of each ferromagnetic mass, and wherein said pulseshaper circuit includes threshold means responsive to said output signal for deriving first and second out of phase pulse-type signals of the same polarity, and means for combining said first and second pulse-type signals to produce a single output pulse signal for each passing ferromagnetic mass.
Dependencies are inferred from the claim text.