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Anonymous
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DISCLOSURE
This invention comprises means for adding the feature of reactive discrimination to a pulse induction metal detector. It is particularly well suited for manufacture as an aftermarket accessory.
It will be appreciated that the invention is, in effect, a method for operating a PI metal detector as a VLF metal detector.
PREFERRED EMBODIMENT #1
This embodiment presupposes that there are separate transmitter and receiver coils, and that the receiver coil is in a condition of induction balance with respect to the transmitter.
In a pulse induction metal detector, it is customary to minimize the capacitance of the receiver coil circuit in order to maintain sensitivity to small targets.
By providing a parallel resonant capacitor, and damping resistor if necessary, reactive signals received during the transmit-flyback period can be extended into the receiver timing. These reactive signals have a polarity which depends on whether they are of ferrous or nonferrous character, and can be demodulated to determine the probable character of the target.
It may be necessary or desirable to add electronic switching to vary the receiver coil circuit parameters during the transmit-flyback-receive sequence in order to maintain compatibility with the dynamic range of the receiver electronics; and/or to optimize sensitivity or discrimination or other desirable characteristic.
Presumably, a switch would be provided to enable the operator to search in the normal fashion, and to select discrimination when checking a target already located.
PREFERRED EMBODIMENT #2
This embodiment presumes that the preexisting system uses separate transmitter and receiver coils. The receiver coil may or may not be in a condition of induction balance relative to the transmitter.
To the preexisting system, add an additional coil which is in induction balance relative to the transmitter, but inductively coupled to the receiver.
A capacitor and (if necessary) a damping resistor are connected to the additional coil to produce resonance at a frequency which will produce the desired responses in the metal detector system in question.
Normally a switch would be provided to allow the operator to select between normal and discriminator operation.
PREFERRED EMBODIMENT #3
This embodiment presupposes that the basis system uses the same coil for both transmitting and receiving.
At least two additional coils are furnished; which, by means of an electronic switch, can be converted from a condition of induction balance to a condition of inductive coupling. Capacitors and resistors are also furnished to provide the desired timing and damping characteristics.
During transmit and flyback, the electronic switch connects the additional coils in the induction balance configuration. Energy from target signals is stored in the LC circuit. During the receive period, the electronic switch changes the configuration of the coils to one of inductive coupling, allowing the stored energy to induce signals into the main coil.
PREFERRED EMBODIMENT #4
The foregoing embodiments, with active circuits added for altering the waveform of the signal induced from the added coil(s) into the receiver coil, in order to improve operating characteristics beyond what can easily be achieved by passive means.
--Dave J.
This invention comprises means for adding the feature of reactive discrimination to a pulse induction metal detector. It is particularly well suited for manufacture as an aftermarket accessory.
It will be appreciated that the invention is, in effect, a method for operating a PI metal detector as a VLF metal detector.
PREFERRED EMBODIMENT #1
This embodiment presupposes that there are separate transmitter and receiver coils, and that the receiver coil is in a condition of induction balance with respect to the transmitter.
In a pulse induction metal detector, it is customary to minimize the capacitance of the receiver coil circuit in order to maintain sensitivity to small targets.
By providing a parallel resonant capacitor, and damping resistor if necessary, reactive signals received during the transmit-flyback period can be extended into the receiver timing. These reactive signals have a polarity which depends on whether they are of ferrous or nonferrous character, and can be demodulated to determine the probable character of the target.
It may be necessary or desirable to add electronic switching to vary the receiver coil circuit parameters during the transmit-flyback-receive sequence in order to maintain compatibility with the dynamic range of the receiver electronics; and/or to optimize sensitivity or discrimination or other desirable characteristic.
Presumably, a switch would be provided to enable the operator to search in the normal fashion, and to select discrimination when checking a target already located.
PREFERRED EMBODIMENT #2
This embodiment presumes that the preexisting system uses separate transmitter and receiver coils. The receiver coil may or may not be in a condition of induction balance relative to the transmitter.
To the preexisting system, add an additional coil which is in induction balance relative to the transmitter, but inductively coupled to the receiver.
A capacitor and (if necessary) a damping resistor are connected to the additional coil to produce resonance at a frequency which will produce the desired responses in the metal detector system in question.
Normally a switch would be provided to allow the operator to select between normal and discriminator operation.
PREFERRED EMBODIMENT #3
This embodiment presupposes that the basis system uses the same coil for both transmitting and receiving.
At least two additional coils are furnished; which, by means of an electronic switch, can be converted from a condition of induction balance to a condition of inductive coupling. Capacitors and resistors are also furnished to provide the desired timing and damping characteristics.
During transmit and flyback, the electronic switch connects the additional coils in the induction balance configuration. Energy from target signals is stored in the LC circuit. During the receive period, the electronic switch changes the configuration of the coils to one of inductive coupling, allowing the stored energy to induce signals into the main coil.
PREFERRED EMBODIMENT #4
The foregoing embodiments, with active circuits added for altering the waveform of the signal induced from the added coil(s) into the receiver coil, in order to improve operating characteristics beyond what can easily be achieved by passive means.
--Dave J.