Metal detector method and apparatus
First Claim
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1. In a transient electromagnetic or pulse induction type metal detecting apparatus having a receiving coil attached to a sensor, a method of distinguishing between ferromagnetic and conductive materials comprising the steps of:
- monitoring the decay curve of the response of a transient pulse;
generating a best fit of the decay curve using a function that has exponential and power law components; and
utilising said best fit or deviations from said curve as a measure of the likelihood of detection of ferromagnetic or conductive materials by said apparatus.
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Abstract
In a transient electromagnetic or pulse induction type metal detecting apparatus having a receiving coil attached to a sensor, a method and apparatus is disclosed of determining a null point comprising determining a series of post transient output values for the sensor at predetermined times; forming a summation of the output values or their negatives; and altering the predetermined times so as to minimise the summation.
26 Citations
11 Claims
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1. In a transient electromagnetic or pulse induction type metal detecting apparatus having a receiving coil attached to a sensor, a method of distinguishing between ferromagnetic and conductive materials comprising the steps of:
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monitoring the decay curve of the response of a transient pulse;
generating a best fit of the decay curve using a function that has exponential and power law components; and
utilising said best fit or deviations from said curve as a measure of the likelihood of detection of ferromagnetic or conductive materials by said apparatus.
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2. In a transient electromagnetic or pulse induction type metal detecting apparatus having a receiving coil attached to a sensor, a method of distinguishing between ferromagnetic and conductive materials comprising the steps of:
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utilising a series of transient pulses of different length;
monitoring the decay curve of the response to each of said transient pulses;
comparing the decay curve of different length transient pulses to a function having exponential and power law components; and
utilising said comparison as an indicator of the type of material detected by said apparatus.
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3. An apparatus for detecting a metal or mineral object in a surrounding medium with a reduced sensitivity to external electromagnetic interference comprising:
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a transmission search coil for transmitting a magnetic field;
a transmission apparatus for energising the transmission search coil with a substantially rectangular voltage producing a pulsed waveform;
a receive coil for detecting the changes in the surrounding magnetic field through a voltage induced across the receive coil by changes in the magnetic flux;
a measuring means for measuring the voltage across the receive coil at 3 or more selected time intervals after the end of a transmission pulse; and
a processing means for processing said voltages such that a null summation is produced for a target medium by altering the time intervals and linearly combining the voltages across the receive coil at the time intervals to produce a ground balanced null signal substantially satisfying the following equations - View Dependent Claims (10)
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4. An apparatus for detecting a metal or mineral object in a surrounding medium comprising:
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a transmission search coil for transmitting a magnetic field;
a transmission apparatus for energising the transmission search coil with a substantially rectangular voltage waveform producing a pulsed waveform that has pulses of two different, widths;
a receive coil for detecting the changes in the surrounding magnetic field through a voltage induced across the coil by changes in the magnetic flux a measuring means for measuring the voltage across the receive coil at a selected time interval after the end of a transmission pulse, the time interval being alterable;
a processing means of processing the said voltages, and altering the transmission pulse width, and altering the receive timing interval such that a null summation is produced for a target medium. - View Dependent Claims (5)
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6. An apparatus for detecting a metal or mineral object in a surrounding medium with reduced sensitivity to ferromagnetic materials comprising:
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a transmission search coil for transmitting a magnetic field;
a transmission apparatus for energising the transmission search coil with a substantially rectangular voltage waveform producing a pulsed waveform that has pulses of two different, widths;
a receive coil for detecting the changes in the surrounding magnetic field through a voltage induced across the receive coil by changes in the magnetic flux;
measuring means for measuring the voltage across the receive coil at two selected time intervals after the end of a transmission pulse, the time intervals being alterable;
processing means for processing the said voltages, altering the transmission pulse width, and altering the receive timing interval such that a null summation is substantially produced for a target medium. - View Dependent Claims (7)
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8. An apparatus for detecting a metal or mineral object in a surrounding medium with reduced sensitivity to ferromagnetic materials comprising:
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a transmission coil for transmitting a magnetic field;
a transmission apparatus for energising the search coil with a substantially rectangular voltage producing a pulsed waveform that has pulses of at least three different, widths;
a receive coil for detecting the changes in the surrounding magnetic field through a voltage induced across the receive coil by changes in the magnetic flux;
measurement means for measuring the voltage across the receive coil at two selected time intervals after the end of a transmission pulse, the time intervals being alterable; and
processing means for processing the said voltages, altering the transmission pulse width, and altering the receive timing interval such that a null summation is produced for a target medium. - View Dependent Claims (9)
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11. An apparatus for detecting a metal or mineral object in a surrounding medium with a reduced sensitivity to external electromagnetic interference comprising:
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a transmission search coil for transmitting a magnetic field;
a transmission apparatus for energising the transmission search coil with a substantially rectangular voltage producing a pulsed waveform;
a receive coil for detecting the changes in the surrounding magnetic field through a voltage induced across the receive coil by changes in the magnetic flux;
a measuring means for measuring the voltage across the receive coil at 3 or more selected time intervals after the end of a transmission pulse; and
a processing means for processing said voltages and altering the time intervals such that a null summation is produced for a target medium by comparing the measured voltages at given sample intervals to a power law and to an exponential law.
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Specification