Magnetometer circuit for measuring the period of beat frequency maxima

• US 4,641,094 A
• Filed: 04/16/1984
• Issued: 02/03/1987
• Est. Priority Date: 04/16/1984
• Status: Expired due to Term

• Current Assignee: Murphy L. Dalton Jr
• Original Assignee: Murphy L. Dalton Jr
• Inventors: Dalton, Murphy L. Jr.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Oldham, Scott M.
• Application Number:
  US06/600,955
• Time in Patent Office: 1,023 Days
• Field of Search: 324/302, 324/301, 324/328, 324/260, 324/304, 324/77 A, 324/253-255, 324/329, 324/236, 324/239, 307/234, 307/522, 307/518, 307/362, 328/111, 328/109, 328/140
• US Class Current: 324/302
• CPC Class Codes: G01R 33/022 Measuring gradient
• CPC Class Codes: G01R 33/24 for measuring direction or magnitude of magnetic fields or magnetic flux

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.

Claims

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, 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.

2. The magnetometer circuit recited in claim 1 wherein said means for threshold detecting comprises a comparator having said threshold voltage as a first input and said beat signal pulses as a second input and producing said detected signal at the output thereof.

3. The magnetometer circuit as recited in claim 1 wherein said means for producing output pulses comprises an integrator circuit for integrating said detected signal and producing an integrated output signal having pulses corresponding to said beat frequency signal pulses.

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:

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.

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:

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.

6. The method recited in claim 5 wherein the step of threshold detecting comprises comparing said beat frequency signal to a selected threshold voltage to produce a detected signal having a first voltage state when said beat frequency signal exceeds said threshold voltage and has a second voltage state when said beat frequency signal is less than said threshold voltage.