Magnetometer circuit for measuring the period of beat frequency maxima
First Claim
1. A magnetometer circuit for use in a magnetic field detector having polarizable bodies in spaced apart relation, each body having a coil wound thereabout for receiving periodic polarizing current pulses, the coils connected to detector circuitry for producing a beat frequency signal having a response pulse following each of the current pulses, each response pulse having a maximum time width related to the difference in magnetic fields at the bodies, the circuit comprising:
- means for threshold detecting said beat frequency signal pulses to produce a detected signal having a first state when said beat frequency signal pulse exceeds a selected threshold voltage and having a second state when said beat frequency signal pulse is less than said threshold voltage, andmeans for producing respective output pulses for said first states of said detected signal, each said output pulse having an amplitude corresponding to the duration of the corresponding first state of said detected signal for producing constant amplitude output pulses to indicate a no-target background and for producing output pulses having a different amplitude from that of said constant amplitude to indicate detection of the target by said magnetometer circuit.
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Abstract
A conventional magnetometer produces an output signal (10) which comprises a series of pulses (12, 14, 16). Each of these pulses has a beat frequency maximum. These pulses are input to a comparator (50) which makes a comparison to a threshold voltage V0 to produce a bi-level detected signal at a line (62). The detected signal is input to an integrator (52) which produces a series of pulses (78, 80, 82) corresponding respectively with the magnetometer output signal pulses (12, 14, 16). The two states of the detected signal corresponding to positive and negative integration. The time period for the positive integration is proportional to the beat frequency maximum time width period for the corresponding magnetometer output signal pulse. Thus the integrated pulses (78, 80, 82) have an amplitude which is a measure of the maxima time width periods for the corresponding magnetometer signal pulses.
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Citations
6 Claims
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1. A magnetometer circuit for use in a magnetic field detector having polarizable bodies in spaced apart relation, each body having a coil wound thereabout for receiving periodic polarizing current pulses, the coils connected to detector circuitry for producing a beat frequency signal having a response pulse following each of the current pulses, each response pulse having a maximum time width related to the difference in magnetic fields at the bodies, the circuit comprising:
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means for threshold detecting said beat frequency signal pulses to produce a detected signal having a first state when said beat frequency signal pulse exceeds a selected threshold voltage and having a second state when said beat frequency signal pulse is less than said threshold voltage, and means for producing respective output pulses for said first states of said detected signal, each said output pulse having an amplitude corresponding to the duration of the corresponding first state of said detected signal for producing constant amplitude output pulses to indicate a no-target background and for producing output pulses having a different amplitude from that of said constant amplitude to indicate detection of the target by said magnetometer circuit. - View Dependent Claims (2, 3)
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4. A magnetometer circuit for use in a magnetic field detector having polarizable bodies in spaced apart relation, each body having a coil wound thereabout for receiving periodic polarizing current pulses, the coils connected to detector circuitry for producing a beat frequency signal having a response pulse following each of the current pulses, each response pulse having a maximum time width related two differences in magnetic fields at the bodies, circuit comprising:
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a first differential amplifier having an inverting input and a noninverting input; a first resistor having a first terminal connected to receive said beat signal and a second terminal connected to the noninverting input of said first amplifier; a second resistor having a first terminal connected to a fixed voltage node; a potentiometer having the resistance element thereof connected between a second terminal of said second resistor and a circuit common point and having a wiper thereof connected to the inverting input of said first differential amplifier wherein a threshold voltage is produced at said wiper; a second differential amplifier having an inverting input and a noninverting input, the output of said first differential amplifier connected to the noninverting input of said second differential amplifier; a third resistor connected between said fixed voltage node and the inverting input of said second differential amplifier; and a capacitor connected between the output and inverting input of said second differential amplifier wherein the output signal from said second differential amplifier is the integral of the output of said first differential amplifier and the amplitude of pulses in said output signal from said second differential amplifier is indicative of the presence or absence of search objects in the region of said detector.
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5. A method for determining the periods of beat frequency maxima in a magnetic field detector having polarized bodies in spaced apart relation, each body having a coil wound thereabout for receiving periodic polarizing current pulses, the coils connected to detector circuitry for producing a beat frequency signal having a response pulse following each of the current pulses, each response pulse having a maximum time width related to the differences in magnetic fields at said bodies, comprising the steps of:
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threshold detecting said beat frequency signal to produce a bi-level detected signal, and producing respective output pulses for each occurrence of a selected state of said detected signal, said output pulses having an amplitude corresponding to the duration of the corresponding occurrence of said selected state in said detected signal, producing a sequence of said output pulses having a constant amplitude to indicate a no-target condition, and producing at least one of said output pulses having an amplitude different from said constant amplitude to indicate detection of a target. - View Dependent Claims (6)
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Specification