JPH05134054A - Metal detecting apparatus - Google Patents

Abstract

PURPOSE:To make it possible to change detecting sensitivity arbitrarily and to perform adjustment by changing the amplitude of the synchronizing signal in synchronous detection without otherwise using an amplifier circuit. CONSTITUTION:An oscillating coil L1 is excited with a high-frequency power supply, and an alternating field is generated. The difference signal, which is obtained with two receiving coils L2, and L3 that are interlinked with the magnetic flux of the magnetic field, is detected with a synchronous signal, whose phase is mutually different. A piece of metal passing between the oscillating coil and the receiving coils is detected based on the respective outputs. Synchronous detecting circuits 20 and 21 comprising the circuits, whose amplification factors are controlled with the magnitudes of the applied voltages are provided. The detected metal signal is demodulated from the difference signal with the synchronizing signal. The voltage amplitude of the synchronizing signal outputted from a synchronizing-signal generating circuit 16 is adjusted, and the detected metal signal is amplified to the arbitrary magnitude.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detecting device,
In particular, the present invention relates to a device that processes a signal from a detection unit including an oscillation coil and two receiving coils that are differentially connected to detect a metal mixed in an object to be inspected.

[0002]

2. Description of the Related Art Conventionally, FIG.
There is one shown in the configuration block diagram of. In the figure, the detection unit 1 includes an oscillating coil L ₁ for generating an alternating magnetic field,
The object to be inspected, which is made up of two receiving coils L ₂ and L ₃ arranged so as to interlink the magnetic flux of the magnetic field, is the oscillation coil L ₁ and the receiving coils L ₂ and L 3. Pass between ₃ and the direction of arrow A.

The oscillation coil L ₁ is, for example, 100 kHz.
Is excited by the high frequency generating circuit 2 to generate a high frequency magnetic flux. The receiving coils L ₂ and L ₃ are arranged so that a part of this magnetic flux is linked in an equal amount. Then, one ends of the receiving coils L ₂ and L 3 are connected in opposite polarities to each other, that is, differentially connected in series, and the other ends are connected to both ends of the variable resistor 3, and the receiving coils L ₂ and L ₃ are connected to each other. _While balancing the real resistance of ₃ , the reception signal of the differential voltage can be obtained from the output terminal 4.

Next, as a signal processing system, 5 is a first-stage amplifier circuit, 6 is a band-pass filter having the same center frequency as the output frequency of the high-frequency generation circuit 2, 7 is a second-stage amplifier circuit, and 8, 9 Is a synchronous detection circuit for demodulating the magnetic and non-magnetic metal detection signals, 10 and 11 are analog filters having the same center frequency as the metal detection signal, and 12 and 13 are voltage comparison circuits for magnetic and non-magnetic metal, respectively. ..

Reference numerals 14 and 15 denote the synchronous detection circuit 8 and
9. First and second phase circuits for changing the phase of the synchronization signal supplied to 9 form a synchronization signal having a phase suitable for detection of magnetic and non-magnetic metal by the first and second phase circuits 14 and 15. To do. Reference numeral 16 denotes a synchronizing signal generating circuit, which has the same frequency as the output frequency of the high frequency generating circuit 2 and is synchronized.

In the metal detecting device having such a structure, the object to be inspected is passed between the oscillation coil L ₁ and the receiving coils L ₂ and L ₃ in the direction of arrow A to detect the metal.
When metal is mixed in the inspection object, the received signal includes a metal detection signal for modulating the frequency for exciting the oscillation coil L ₁ . Since the signal amplified by the amplifier circuit 5 in the first stage also includes many unnecessary signals having different frequencies, these unnecessary signals are removed by a bandpass filter 6 that passes only signals near the excitation frequency. To do. The received signal that has passed through the bandpass filter 6 is amplified by the second-stage amplifier circuit 7.

In order to extract the metal detection signal from this signal, the synchronous detection circuits 8 and 9 have the same frequency as the excitation frequency, but are synchronized by the first and second phase shift circuits 14 and 15 having different phases. Synchronous detection is performed by the signal to demodulate the metal detection signal. The synchronous detection circuits 8 and 9
For, there is a method of synchronous detection using, for example, an analog switch. Next, only the metal detection signal is passed by the analog filters 10 and 11, and the voltage comparison circuits 12 and 13 are passed.
Outputs the detection result of magnetic or non-magnetic metal.

[0008]

By the way, since the metal detection signal included in the received signal is very weak, it is necessary to amplify the signal by the amplifier circuits 5 and 7 in the first and second stages. In addition, when inspecting the inspection object for the presence or absence of metal contamination, it is necessary to change the detection sensitivity depending on the type of the inspection object and the inspection conditions.

In the conventional metal detection device, in order to change the metal detection sensitivity, the amplification degrees of the amplification circuits 5 and 7 of the first and second stages are adjusted to meet the above conditions. Also,
Since the amplifier circuits 5 and 7 are inserted in the signal processing system,
The path for processing the received signal will inevitably become long,
Therefore, there is a problem that noise is likely to be mixed in and the metal detection performance is deteriorated.

The present invention has been made in view of the above points,
It is an object of the present invention to solve the above problems and to provide a metal detection device in which the detection sensitivity can be arbitrarily changed and adjusted by changing the amplitude of the synchronization signal in the synchronous detection without using an amplifier circuit. ..

[0011]

In order to achieve the above object, the structure of the present invention comprises two receiving coils which excite an oscillating coil from a high frequency power source to generate an alternating magnetic field and which interlinks with the magnetic flux of the magnetic field. In the device for detecting the metal passing between the oscillation coil and the receiving coil from each output signal by detecting the difference signal obtained from the synchronization signals having mutually different phases, a multiplication circuit, a voltage control amplifier circuit, etc. As described above, the synchronous detection means including a circuit whose amplification degree is controlled by the magnitude of the applied voltage and the synchronization signal generation means for generating the synchronization signal are provided, and the metal detection signal from the difference signal is generated by the synchronization signal. Is demodulated and the voltage amplitude of the synchronizing signal output from the synchronizing signal generating means is adjusted to amplify the metal detection signal to an arbitrary magnitude.

[0012]

Since the present invention is configured as described above, the metal detection signal after synchronous detection can be amplified to an arbitrary size by adjusting the voltage amplitude of the synchronous signal during synchronous detection. The amplifier circuit that has been inserted into the signal processing system is unnecessary, and the signal processing path is shortened accordingly, so that the mixing of noise is reduced and the detection performance can be improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be illustratively described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the metal detector of the present invention. The same parts as those in FIG. In FIG. 1, reference numerals 20 and 21 are synchronous detection circuits with voltage control amplification.

Oscillation coil L ₁ and receiving coil L of the detector 1
_{When the} object to be inspected passes between ₂ and L ₃ in the direction of arrow A, the received signals from the receiving coils L ₂ and L ₃ have the same metal detection signal as the excitation frequency (the output frequency of the high frequency generation circuit 2). ) Is output in the form of modulating the carrier signal.

The band-pass filter 6 without directly amplifying this signal
And the synchronous detection circuits 20 and 21 each composed of a circuit whose amplification degree can be controlled by a voltage such as a multiplication circuit and a voltage control amplifier circuit are multiplied by the synchronous signal to demodulate the metal detection signal. The frequency of the synchronization signal is the same as the excitation frequency and is synchronized.

Since the metal detection signal contained in the received signal is very weak, it usually needs to be amplified, but the synchronous detection circuits 20 and 21 are applied like a multiplication circuit or a voltage control amplifier circuit. Since the amplification degree is controlled by the voltage, the synchronized detection signal, that is, the metal detection signal can be amplified by increasing the voltage amplitude of the synchronization signal. The sync signal changes the voltage amplitude of the output signal by adjusting the sync signal generating circuit 16. Next, the analog filters 10 and 11
Passes only the demodulated metal detection signal.

From the above, the synchronous detection circuits 20 and 21 are
It is possible to amplify and extract only the metal detection signal by the combination of the analog filter 10 and the analog filter 10 and 11. The metal detection signal that has passed through the analog filters 10 and 11 is
Similar to the conventional metal detection device, the voltage comparison circuits 12 and 13
Outputs the detection result of magnetic or non-magnetic metal.

Note that the technique of the present invention is not limited to the technique in the above-described embodiment, and may be implemented by means of another aspect having a similar function, and the technique of the present invention can be variously modified within the scope of the configuration. Can be changed or added.

[0019]

As is apparent from the above description, according to the metal detector of the present invention, the amplification degree is controlled by the magnitude of the applied voltage, such as the multiplication circuit and the voltage control amplifier circuit. Since the synchronous detection means and the synchronous signal generation means for generating the synchronous signal are provided, the demodulation metal detection signal is obtained by adjusting the voltage amplitude of the synchronous signal while performing synchronous detection without the need for an amplifier circuit. Can be amplified to any size. That is, the sensitivity for metal detection can be arbitrarily changed and adjusted.

Further, with the shortening of the signal processing path, there is an excellent result that the mixing of noise can be reduced and the improvement of metal detection performance can be expected.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of a metal detection device of the present invention.

FIG. 2 is a configuration block diagram of a conventional metal detection device.

[Explanation of symbols]

L ₁ oscillator coil L ₂ , L ₃ receiver coil 14, 15 phase shift circuit 16 sync signal generation circuit 20, 21 voltage detection synchronous detection circuit with amplification

Claims (1)

[Claims] 1. An oscillating coil is excited from a high frequency power source to generate an alternating magnetic field, and a difference signal obtained from two receiving coils interlinking with a magnetic flux of the magnetic field is detected by synchronizing signals having mutually different phases, In a device for detecting a metal passing between the oscillation coil and the receiving coil from each output signal, the synchronous detection means including a circuit whose amplification degree is controlled by the magnitude of the applied voltage, and the synchronization signal Sync signal generating means for generating the metal detection signal from the difference signal according to the sync signal, and adjusting the voltage amplitude of the sync signal output from the sync signal generating means to detect the metal detection signal. A metal detection device, which amplifies an arbitrary size.