JPH05134052A - Metal detecting apparatus - Google Patents

Abstract

PURPOSE:To make it possible to change detecting sensitivity arbitrarily and to perform adjustment by charging the amplitude of the frequency converting signal in frequency conversion without otherwise using an amplifier circuit. CONSTITUTION:An oscillating coil L1 is excited with a high-frequency power supply, and the alternating field is generated. The high frequency of 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 converted into the other constant frequency, which is different from the above described frequency. The signal is detected with a synchronizing signal whose phase is mutually different. A piece of metal passing between the oscillating coil and the receiving coils is detected with the respective output signals. Frequency converting means 18 and 20 comprising the circuits, whose amplification factors are controlled with the magnitudes of the applied voltages, are provided. The voltage amplitude of the frequency conversism signal is adjusted, and the difference signal after the frequency conversion 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.
It is excited by the high frequency generating circuit 2 for z to generate 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, the one end opposite polarities of the reception coil L _2, L _3, i.e. the difference is dynamically connected in series, and the other end is connected to both ends of the variable resistor 3 to each other, each receiving coil L _2, L The balance of the real resistance of ₃ is taken, and the reception signal of the differential voltage is obtained from the output terminal 4.

Next, as a signal processing system, 5 is an amplifier circuit in the first stage, 6 is a frequency conversion circuit for converting a high frequency frequency in the received signal to another frequency, and 7 is the high frequency generation circuit 2.
A bandpass filter with the same center frequency as the output frequency of
8 is a second stage amplifier circuit, 9 and 10 are synchronous detection circuits for demodulating magnetic and non-magnetic metal detection signals, 11 and 12, respectively.
Is an analog filter having the same center frequency as the metal detection signal, and 13 and 14 are voltage comparison circuits for magnetic and non-magnetic metals, respectively.

Reference numerals 15 and 16 denote the synchronous detection circuit 9 and
First and second phase shift circuits for changing the phase of the sync signal supplied to the synchronization signal supplied to the first and second phase shift circuits 15 and 16 which are suitable for detection of magnetic and non-magnetic metals. To form. Reference numeral 17 denotes a synchronizing signal generation circuit, and 18 denotes a frequency conversion signal generation circuit for supplying a conversion signal to the frequency conversion circuit 6. The frequency of the synchronizing signal supplied from the synchronizing signal generating circuit 17 is the same as the frequency after frequency conversion 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 . First, the received signal is the first stage amplification circuit 5
Is amplified by.

Where f _d is the frequency of the metal detection signal and f _g
Is the excitation frequency for the carrier signal of the metal detector. The received signal amplified by the amplifier circuit 5 in the first stage is fed by the frequency conversion circuit 6 with a signal of frequency f _t + f _g or f _t −f _g supplied from the frequency conversion signal generation circuit 18.
Convert to another frequency f _t . The frequency-converted reception signal is the carrier detection frequency f _t after frequency conversion by the metal detection signal.
The signal is modulated. Here, the frequency conversion circuit 6
Is a circuit that mixes two signals, such as a signal mixer circuit and a balanced modulation circuit.

The band-pass filter 7 is for passing only a necessary signal and removing an unnecessary signal, and the center frequency of the band-pass filter 7 is the frequency of the received signal, that is, the frequency f _t after the above frequency conversion. To match.

The received signal, after passing through the bandpass filter 7,
It is amplified by the second-stage amplifier circuit 8. Next, this signal is detected by the synchronous detection circuits 9 and 10 to demodulate the metal detection signal. The frequency of the sync signal for synchronous detection is
It is the same as the frequency f _t after the frequency conversion and is synchronized. The phase of the synchronization signal is the first,
The second phase shift circuits 15 and 16 shift the phases to mutually different phases.

Of the signals synchronously detected, only the metal detection signal is passed by the analog filters 11 and 12,
The voltage comparison circuits 13 and 14 output the detection result of magnetic or non-magnetic metal.

[0011]

By the way, since the metal detection signal contained in the received signal is very weak, it is necessary to amplify the signal by the amplifier circuits 5 and 8 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 8 in the first and second stages are adjusted to meet the above conditions. Further, since the amplifying circuits 5 and 8 are inserted in the signal processing system, the path through which the received signal passes is inevitably long, which increases the possibility that noise is mixed in, and lowers the metal detection performance. There was a problem.

The present invention has been made in view of the above points,
An object of the present invention is to solve the above problems and provide a metal detection device capable of arbitrarily changing and adjusting the detection sensitivity by changing the amplitude of a frequency conversion signal in frequency conversion without using an amplifier circuit. Especially.

[0014]

The structure of the present invention for achieving the above-mentioned object is to provide two receiving coils which excite an oscillating coil from a high frequency power source to generate an alternating magnetic field and interlink with the magnetic flux of the magnetic field. The high frequency of the difference signal obtained from
In a device for converting to another constant frequency different from the frequency, detecting the signals by synchronizing signals having mutually different phases, and detecting the metal passing between the oscillation coil and the receiving coil from the respective output signals. , A frequency conversion means including a circuit whose amplification degree is controlled by the magnitude of the applied voltage, such as a multiplication circuit or a voltage control amplifier circuit,
It is characterized in that the voltage amplitude of the frequency conversion signal in the means is adjusted to amplify the difference signal after frequency conversion to an arbitrary magnitude.

[0015]

Since the present invention is configured as described above, when the high frequency of the received signal output from the receiving coil is frequency-converted, the voltage amplitude of the frequency-converting signal is adjusted to adjust the frequency of the received signal. Since the received signal can be amplified, the amplifier circuit inserted in the conventional signal processing system becomes unnecessary, and the signal processing path is shortened accordingly, so that the mixing of noise is reduced and the detection performance is improved. You can

[0016]

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 numeral 20 is a frequency conversion circuit with voltage control amplification for converting a received signal into another frequency.

Oscillation coil L ₁ and reception 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 frequency f _g (high frequency generation circuit 2) as the metal detection signal as the excitation frequency.
The output signal is output by modulating the carrier signal.

This signal is supplied from the frequency converting signal generating circuit 18 by a frequency converting circuit 20 composed of a circuit such as a multiplying circuit and a voltage control amplifier circuit whose amplification degree can be controlled by the applied voltage. The signal for frequency conversion is multiplied and converted to another frequency f _t .

Since the metal detection signal included in the received signal is very weak, it usually needs to be amplified, but the frequency conversion circuit 20 is amplified by the applied voltage like a multiplication circuit, a voltage control amplifier circuit, or the like. Since the circuit is composed of a circuit whose frequency is controllable, it can be amplified by increasing the voltage amplitude of the frequency conversion signal. The frequency conversion signal changes the voltage amplitude of the signal output by the adjustment of the frequency conversion signal generation circuit 18.

After frequency conversion, like the conventional metal detector, after removing unnecessary signals by the bandpass filter 7,
The synchronous detection circuits 9 and 10 demodulate the metal detection signal, the analog filters 11 and 12 pass only the metal detection signal, and the voltage comparison circuits 13 and 14 output the detection result of magnetic or nonmagnetic 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 above configuration. Can be changed or added.

[0022]

As is apparent from the above description, according to the metal detecting device of the present invention, when the high frequency of the reception signal output from the receiving coil of the detecting section is frequency-converted,
Since the frequency conversion means including a circuit whose amplification degree is controlled according to the magnitude of the applied voltage, such as a multiplication circuit or a voltage control amplification circuit, is provided, another amplification circuit is not required and Adjust the voltage amplitude of the frequency conversion signal,
The received signal after frequency conversion can be amplified to an arbitrary size.
That is, the sensitivity for metal detection can be arbitrarily changed and adjusted.

Further, with the shortening of the signal processing path, it is possible to reduce the mixing of noise and it is possible to expect an improvement in metal detection performance.

[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 and L ₃ receiver coil 18 frequency conversion signal generation circuit 20 frequency conversion circuit with voltage control amplification

Claims (1)

[Claims] 1. An oscillating coil is excited from a high frequency power source to generate an alternating magnetic field, and the high frequency frequency of a difference signal obtained from two receiving coils interlinking with a magnetic flux of the magnetic field is different from the high frequency frequency. In a device that converts to a constant frequency, detects the signals by synchronizing signals with different phases, and detects the metal passing between the oscillation coil and the receiving coil from each output signal, the magnitude of the applied voltage A frequency conversion means composed of a circuit whose amplification degree is controlled by adjusting the voltage amplitude of the frequency conversion signal in the means to amplify the difference signal after frequency conversion to an arbitrary magnitude. Metal detection device characterized by.