Metal detector and its receiving circuit and detection circuit

Abstract

The present invention relates to a metal detector and a receiving circuit and a detection circuit thereof, wherein the receiving circuit includes a selection switch and a plurality of receiving units, wherein each receiving unit is composed of two receiving coils symmetrically arranged at both ends of a transmitting coil, and the transmitting coil and all the receiving coils are arranged in a straight line, the control signal input end of the selection switch is connected to a host computer, and each receiving unit is selectively connected to an output end through the selection switch. Compared with the prior art, the present invention provides multiple groups of receiving units to selectively connect to the next level, thereby providing different signal frequencies, thereby filtering out vibration interference that is originally the same as the signal frequency.

Description

Technical Field

[0001] The invention relates to anti-vibration and anti-interference technology for metal detectors, and in particular to a metal detector and a receiving circuit and a detection circuit thereof. Background Art

[0002] The metal detector will have a certain inherent oscillation frequency when it is disturbed by external vibrations. The vibrations will cause the machine to give false alarms and affect the use of the machine.

[0003] In the prior art, the metal detector improves the anti-interference performance by designing a demodulation circuit. However, sometimes, the frequency of the signal generated by mechanical vibration is very close to the signal frequency of the product, and it is difficult to filter it out through a filtering circuit. The distance between the transmitting coil and the receiving coil is fixed, and the frequency of the signal generated when the coil passes through at a fixed speed is fixed. If the frequency of the interference or the frequency of the vibration is the same as the signal frequency, it may interfere with the product detection, and it is difficult to filter out the interference. Summary of the invention

[0004] The receiving unit of the metal detector contains two receiving coils, which are symmetrically arranged at both ends of the transmitting coil. Under normal circumstances, when the metal object passes through the first receiving coil, the response signal will reach a maximum value, and when it passes through the second receiving coil, the signal will reach a minimum value. After processing, the response signal can be approximately equivalent to a sine wave of a certain frequency, and the frequency of the signal response changes with the speed at which the metal interference object passes.

[0005] Assume that the distance between the two receiving coils of the receiving unit is S, the speed of the metal object is V, and the time it takes for the metal to pass through the first receiving coil and leave the second receiving coil is half a cycle. Therefore, it can be seen that the signal period T = 2*S / V, and correspondingly, the frequency f = V / (2*S). Therefore, the signal frequency is directly related to the distance and speed between the two receiving coils. However, the change of the speed factor cannot be changed at will due to production and other factors. Especially for machines with non-uniform speed operation such as drop-type metal detectors, the speed factor is even more fixed. If low-frequency interference such as vibration is close to the signal frequency, it is difficult to filter out the interference signal through the later filtering circuit.

[0006] The purpose of the present invention is to provide a metal detector and its receiving circuit and detection circuit, which can solve the problem in the prior art that the metal detector cannot filter out vibration and interference frequencies that are the same as the signal frequency.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A metal detector receiving circuit comprises a selection switch and a plurality of receiving units, wherein each receiving unit is composed of two receiving coils symmetrically arranged at both ends of a transmitting coil, and the transmitting coil and all the receiving coils are arranged in a straight line, the control signal input end of the selection switch is connected to a host computer, and each receiving unit is selectively connected to an output end through the selection switch.

[0009] There are two receiving units in total, the selection switch is a relay, the coil of the relay is connected to the host computer, the normally closed end and the normally open end are respectively connected to the two receiving units, and the common end is connected to the output end.

[0010] A metal detector detection circuit includes a receiving circuit and a demodulation circuit. The receiving circuit includes a selection switch and multiple receiving units, wherein each receiving unit is composed of two receiving coils symmetrically arranged at both ends of a transmitting coil, and the transmitting coil and all the receiving coils are arranged in a straight line. The control signal input end of the selection switch is connected to a host computer, and each receiving unit is selectively connected to the demodulation circuit through the selection switch.

[0011] However, as far as the number of receiving units is concerned, as long as there are more than two, there is no essential difference in solving the above-mentioned technical problems. However, in order to reduce costs, preferably, the receiving units are provided with two in total, the selection switch is a relay, the coil of the relay is connected to the host computer, the normally closed end and the normally open end are respectively connected to the two receiving units, and the common end is connected to the demodulation circuit.

[0012] The demodulation circuit includes a multiplication circuit, a first filtering circuit, a second filtering circuit and an amplification circuit which are connected in sequence.

[0013] The first filter circuit and the second filter circuit are both second-order active filter circuits.

[0014] A metal detector comprises a host computer, a receiving circuit and a demodulation circuit, wherein the receiving circuit comprises a selection switch and a plurality of receiving units, wherein each receiving unit is composed of two receiving coils symmetrically arranged at both ends of a transmitting coil, and the transmitting coil and all the receiving coils are arranged in a straight line, the control signal input end of the selection switch is connected to the host computer, and each receiving unit is selectively connected to the demodulation circuit through the selection switch, and the demodulation circuit is connected to the host computer.

[0015] There are two receiving units in total, the selection switch is a relay, the coil of the relay is connected to the host computer, the normally closed end and the normally open end are respectively connected to the two receiving units, and the common end is connected to the demodulation circuit.

[0016] The demodulation circuit includes a multiplication circuit, a first filtering circuit, a second filtering circuit and an amplification circuit which are connected in sequence.

[0017] The first filter circuit and the second filter circuit are both second-order active filter circuits.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) By setting up multiple groups of receiving units and selecting one to connect to the next level, different signal frequencies can be provided, thereby filtering out vibration interference that is originally the same as the signal frequency.

[0020] 2) Using two receiving units has lower cost.

[0021] 3) By switching different capacitors to form low-pass or band-pass filters with different cut-off frequencies through the analog switch of the demodulation circuit, combined with the switching of the two receiving units, the detection signal is not interfered by external signals of similar frequencies when better adapting to the interference of the external environment, thereby improving the effect of metal detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The signal curve for metal;

[0023] Figure 2 This is a schematic diagram of the coil arrangement of the receiving circuit of this application;

[0024] Figure 3 This is a schematic diagram of the electrical part of the metal detector for this application;

[0025] Figure 4 Schematic diagram of the demodulation circuit. DETAILED DESCRIPTION

[0026] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0027] like Figure 1 As shown, when the metal object passes through the first receiving coil 201, the maximum value of the response signal is generated, and when it passes through the second receiving coil 202, the signal is at a minimum value. After processing, the response signal can be approximately equivalent to a sine wave of a certain frequency, and the frequency of the signal response X changes with the change of the speed at which the metal interference object passes.

[0028] The present application provides a metal detector, such as Figure 3 As shown, it includes a host computer 6, a receiving circuit and a demodulation circuit 5, the receiving circuit includes a selection switch 4 and a receiving unit 2, a receiving unit 3, wherein, as Figure 2As shown, the receiving unit 2 is composed of a receiving coil 201 and a receiving coil 202, and the receiving unit 3 is composed of a receiving coil 301 and a receiving coil 302. The receiving coil 201 and the receiving coil 202 are symmetrically arranged on both sides of the transmitting coil 101, and the receiving coil 301 and the receiving coil 302 are also symmetrically arranged on both sides of the transmitting coil 101, and the receiving coil 301 and the receiving coil 302 are also located outside the receiving coil 201 and the receiving coil 202, and the receiving coil 301, the receiving coil 201, the transmitting coil 101, the receiving coil 202 and the receiving coil 302 are arranged in a straight line. The selection switch adopts a relay 4, the normally open end of the relay 4 is connected to the output end of the receiving unit 2, the normally closed end is connected to the output end of the receiving unit 3, the coil is connected to the host computer 6 and is controlled by the host computer 6 to be turned on or off, and the common end is connected to the demodulation circuit 5. The relay 4 realizes that the outputs of the receiving units 2 and 3 are sent to the demodulation circuit 5 according to the control signal of the host computer 6.

[0029] The specific selective control process is: the output signal of the receiving unit 3 is used by default, and when the vibration frequency is too close to the signal frequency at this time, the coil of the control relay 4 is turned on, thereby switching to the output signal of the receiving unit 2.

[0030] In another embodiment of the present application, the normally open end of the relay 4 is connected to the output end of the receiving unit 3 , and the normally closed end is connected to the output end of the receiving unit 2 .

[0031] In other embodiments of the present application, the number of receiving units is not limited to two, and may be 3, 4 or more.

[0032] like Figure 4 As shown, 521 and 522 are two multi-way switches of the first filter circuit 52, and 531 and 532 are two multi-way switches of the second filter circuit 53. The demodulation circuit includes a multiplication circuit 51, a first filter circuit 52, a second filter circuit 53 and an amplifier circuit 54 connected in sequence. The first filter circuit 52 and the second filter circuit 53 are both second-order active filter circuits. The second-order active filter circuit is composed of a second-order active filter, and appropriate resistors and capacitors, so as to form high-pass and low-pass filters with different cut-off frequencies, so as to realize the formation of band-pass or low-pass circuits with different cut-off frequencies and different Q values. By switching different capacitors to form low-pass or band-pass filters with different cut-off frequencies through analog switches, combined with the switching of two groups of receiving units, it is used to better adapt to the interference of the external environment. The detection signal is not interfered by the external similar frequency signal, thereby improving the effect of metal detection.

[0033] In other embodiments of the present application, an automatic switching device controlled by a host computer can also be designed to adjust the filtering parameters and a device for automatically switching the coil spacing to achieve separation of signal frequency and interference frequency so as to better distinguish the corresponding signal from the interference signal, thereby filtering out the interference.

[0034] In other embodiments of the present application, the receiving circuit can be replaced as an independent accessory.

Claims

1. A metal detector receiving circuit, characterized in that: It includes a selection switch and a plurality of receiving units, wherein each receiving unit is composed of two receiving coils symmetrically arranged at both ends of a transmitting coil, and the transmitting coil and all the receiving coils are arranged in a straight line, the control signal input end of the selection switch is connected to a host computer, and each receiving unit is selectively connected to an output end through the selection switch; There are two receiving units in total, the selection switch is a relay, the coil of the relay is connected to the host computer, the normally closed end and the normally open end are respectively connected to the two receiving units, the common end is connected to the output end, and the distances from the transmitting coil to the receiving coils of different receiving units are different.

2. A metal detector detection circuit, comprising a receiving circuit and a demodulation circuit, characterized in that: The receiving circuit includes a selection switch and a plurality of receiving units, wherein each receiving unit is composed of two receiving coils symmetrically arranged at both ends of the transmitting coil, and the transmitting coil and all the receiving coils are arranged in a straight line, the control signal input end of the selection switch is connected to the host computer, and each receiving unit is selectively connected to the demodulation circuit through the selection switch; There are two receiving units in total, the selection switch is a relay, the coil of the relay is connected to the host computer, the normally closed end and the normally open end are respectively connected to the two receiving units, the common end is connected to the demodulation circuit, and the distances from the transmitting coil to the receiving coils of different receiving units are different.

3. A metal detector detection circuit according to claim 2, characterized in that: The demodulation circuit includes a multiplication circuit, a first filtering circuit, a second filtering circuit and an amplification circuit which are connected in sequence.

4. A metal detector detection circuit according to claim 3, characterized in that: The first filter circuit and the second filter circuit are both second-order active filter circuits.

5. A metal detector, comprising a host computer, a receiving circuit and a demodulation circuit, characterized in that: The receiving circuit includes a selection switch and a plurality of receiving units, wherein each receiving unit is composed of two receiving coils symmetrically arranged at both ends of a transmitting coil, and the transmitting coil and all the receiving coils are arranged in a straight line, the control signal input end of the selection switch is connected to a host computer, and each receiving unit is selectively connected to a demodulation circuit through the selection switch, and the demodulation circuit is connected to the host computer; There are two receiving units in total, the selection switch is a relay, the coil of the relay is connected to the host computer, the normally closed end and the normally open end are respectively connected to the two receiving units, the common end is connected to the demodulation circuit, and the distances from the transmitting coil to the receiving coils of different receiving units are different.

6. A metal detector according to claim 5, characterized in that: The demodulation circuit includes a multiplication circuit, a first filtering circuit, a second filtering circuit and an amplification circuit which are connected in sequence.

7. A metal detector according to claim 6, characterized in that: The first filter circuit and the second filter circuit are both second-order active filter circuits.

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