Balancing signal adjusting system of metal detector

Abstract

The invention discloses a metal detector balance signal adjusting system which comprises a receiving coil, a receiving transformer, a receiving amplifying circuit and a signal remaking circuit. The signal remaking circuit comprises a carrier signal generator, a first multiplier, a second multiplier, a first low-pass filtering and amplifying circuit, a second low-pass filtering and amplifying circuit, an AD sampling circuit, a control module, a first DA digital-to-analog converter, a second DA digital-to-analog converter and a signal adder. The control module is used for controlling the DA converter to generate the reproduced analog signal corresponding to the balance signal, and the balance signal is adjusted, so that the balance stability is improved, the detection precision of the metal detector is improved, and the adjustment duration of the metal detector is shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of metal detection, and in particular relates to a balanced signal adjustment system for a metal detector. Background Art

[0002] The metal detector processes the balanced signal to detect metal foreign objects.

[0003] Generally, balanced signals can be obtained in the following ways. The transmitting signal is amplified by the power amplifier circuit and then sent to the transmitting coil through the transmitting transformer, generating an electromagnetic field of a certain intensity in the probe. The receiving coil senses the change of the electromagnetic field, and its output enters the receiving amplifier circuit through the receiving transformer and outputs a balanced signal. The balanced signal and the orthogonal carrier signal generated by the carrier signal generator are input into the multiplier. The output signal of the multiplier is filtered and amplified to obtain the DT1 and DT2 signals for sampling, which are sent to the CPU after AD sampling.

[0004] The size of the balanced signal is very important for subsequent signal processing. If the balanced signal is too large, it will cause the subsequent op amp circuit to saturate, making the final output signal unable to detect metal foreign matter. At the same time, the larger the balanced signal, the lower the symmetry level of the receiving coil in the coil system, and the lower the ability to suppress external differential mode interference.

[0005] During use, the balance signal will also change because the state of the probe coil may change (such as temperature changes, external shocks, etc.). Generally, the balance is adjusted by manually adding metal to the probe window (fixing measures are taken on the metal in the window after the adjustment is completed), or an electronic adjustment module (usually a potentiometer) is set up to manually perform zeroing operations. When the equipment requires manual intervention, it is actually when maintenance is required. The above methods for dealing with balance changes all require manual participation and cannot be completed automatically. Therefore, once the problem of a larger balance signal occurs, a technician is required to repair and debug the metal detector, which will obviously significantly advance the first maintenance time of the equipment, increase the cost of the equipment, and reduce the ease of use of the equipment and its competitiveness in the market. For this reason, there is an urgent need for a method that can automatically adjust the balance to improve the balance stability. Summary of the invention

[0006] The purpose of the present invention is to provide a metal detector balance signal adjustment system in order to overcome the defects of the prior art.

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

[0008] On the one hand, the present invention provides a balanced signal adjustment system for a metal detector, comprising a receiving coil, a receiving transformer, a receiving amplifier circuit, and a signal reproducing circuit, wherein the receiving transformer comprises an auxiliary winding, and the signal reproducing circuit comprises a carrier signal generator, a first multiplier, a second multiplier, a first low-pass filter amplifier circuit, a second low-pass filter amplifier circuit, an AD sampling circuit, a control module, a first DA digital-to-analog converter, a second DA digital-to-analog converter, and a signal adder, wherein the output end of the signal adder is connected to the auxiliary winding, the output end of the receiving amplifier circuit is connected to the input end of the first multiplier and the input end of the second multiplier, and the carrier signal generator is respectively The first multiplier input terminal is connected to the second multiplier input terminal, the first multiplier output terminal is connected to the first low-pass filter amplifier circuit input terminal, the first low-pass filter amplifier circuit output terminal is connected to the AD sampling circuit input terminal, the second multiplier output terminal is connected to the second low-pass filter amplifier circuit input terminal, the second low-pass filter amplifier circuit output terminal is connected to the AD sampling circuit input terminal, the AD sampling circuit output terminal is connected to the control module, the control module is controlled and connected to the first DA digital-to-analog converter and the second DA digital-to-analog converter, and the first DA digital-to-analog converter output terminal and the second DA digital-to-analog converter output terminal are connected to the signal adder.

[0009] Furthermore, the carrier signal input to the first multiplier by the carrier signal generator is a first carrier signal, the carrier signal input to the second multiplier by the carrier signal generator is a second carrier signal, and the first carrier signal is orthogonal to the second carrier signal.

[0010] Furthermore, the AD sampling circuit is used to receive a first balanced signal after the balanced signal is multiplied, filtered and amplified by the first carrier signal, and a second balanced signal after the balanced signal is multiplied, filtered and amplified by the second carrier signal, and to sample the first balanced signal and the second balanced signal to output a first balanced digital signal and a second balanced digital signal.

[0011] Furthermore, the first balanced digital signal and the second balanced digital signal output by the AD sampling circuit include amplitude information and phase information of the balanced signals.

[0012] Furthermore, the control module includes a storage unit.

[0013] Furthermore, the storage unit is used to store the first balanced digital signal and the second balanced digital signal output by the AD sampling circuit.

[0014] Furthermore, the control module is used to perform the following process:

[0015] Receiving in real time a first balanced digital signal and a second balanced digital signal output by an AD sampling circuit;

[0016] extracting balanced signal amplitudes from the first balanced digital signal and the second balanced digital signal;

[0017] Determine whether the amplitude of the balanced signal is greater than a first threshold value, if so, start timing, if the amplitude of the balanced signal is less than or equal to the first threshold value during the timing stage, the timing is reset to zero, if the timing duration is greater than a third threshold value, control the first DA digital-to-analog converter and the second DA digital-to-analog converter to output a first reconstructed analog signal and a second reconstructed analog signal respectively, the amplitude and phase of the reconstructed analog signal generated by superposition of the first reconstructed analog signal and the second reconstructed analog signal being the same as the balanced signal;

[0018] If the amplitude of the balanced signal is less than or equal to the first threshold, it is determined whether the amplitude of the balanced signal is greater than the second threshold. If it is greater, the timing is started. If the balanced signal is less than or equal to the second threshold during the timing stage, the timing is reset to zero. If the timing duration is greater than the third threshold, the first DA digital-to-analog converter and the second DA digital-to-analog converter are controlled to output the third reconstructed analog signal and the fourth reconstructed analog signal at time intervals equal to the first step according to the reconstructed analog signal output at the previous moment, until the amplitudes of the output third reconstructed analog signal and the fourth reconstructed analog signal are equal to the amplitude of the balanced signal.

[0019] Furthermore, the control module also includes the following execution process: if the amplitude of the balance signal is greater than the first threshold and the duration is greater than the third threshold, the metal detector is controlled to stop detection.

[0020] Furthermore, the first threshold is greater than the second threshold.

[0021] Furthermore, the signal adder is used to superimpose the reconstructed analog signals output by the first DA digital-to-analog converter and the second DA digital-to-analog converter, and output the reconstructed analog signal. The auxiliary winding is used to receive the reconstructed analog signal output by the signal adder, inject the reconstructed analog signal into the receiving transformer, and subtract it from the balanced signal.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention adopts a method combining fast adjustment and slow adjustment. When the balance signal does not exceed the threshold, the slow adjustment is used to slowly adjust the remade analog signal to achieve slow adjustment of the balance signal; when the balance signal exceeds the threshold, the fast adjustment is used to quickly reduce the balance signal. The slow adjustment solves the problem that the metal detector cannot perform normal detection during the adjustment of the balance signal, while the fast adjustment solves the problem that the balance signal increases rapidly, but the slow adjustment cannot quickly adjust the balance signal to a normal level, making the metal detector unable to perform normal detection. By combining the fast adjustment and the slow adjustment, the metal detector can achieve normal detection most of the time, shortening the time for the metal detector to adjust the balance signal.

[0024] (2) The present invention solves the problem of manual adjustment in the prior art by automatically adjusting the balance signal electronically.

[0025] (3) The present invention solves the problem of the inability to detect when adjusting the balance signal in the prior art by combining fast and slow adjustments, and can take into account both real-time response and stability. Fast adjustment can quickly respond to sudden changes in the environment, ensuring immediate feedback and rapid processing; while slow adjustment helps to smooth out long-term minor interference and prevent the system from being too sensitive and causing false alarms. The combination of the two not only improves the accuracy of detection, but also ensures the reliability and stability of the equipment in complex environments, and reduces fluctuations or errors in the system caused by over-adjustment.

[0026] (4) The present invention can effectively improve detection accuracy and stability by adjusting the balanced signal through the auxiliary winding of the receiving transformer. The auxiliary winding can provide additional feedback signals to help compensate for the imbalance in the main winding signal and reduce the impact of external interference, thereby optimizing the sensitivity of the device and ensuring accurate detection of metal objects under different environmental conditions. This adjustment method helps to extend the service life of the device, reduce the false alarm rate, and improve the overall performance, especially when dealing with complex or changing detection environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0028] Figure 2 It is a schematic diagram of the structure of the signal reproducing circuit of the present invention;

[0029] The reference numerals in the figure are: 1. first multiplier, 2. second multiplier, 3. first low-pass filter amplifier circuit, 4. second low-pass filter amplifier circuit, 5. first DA digital-to-analog converter, 6. second DA digital-to-analog converter, 7. signal adder. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0031] The present embodiment provides a balanced signal adjustment system for a metal detector, including a receiving coil, a receiving transformer, a receiving amplifier circuit, and a signal reproducing circuit. The receiving transformer includes an auxiliary winding. The signal reproducing circuit includes a carrier signal generator, a first multiplier, a second multiplier, a first low-pass filter amplifier circuit, a second low-pass filter amplifier circuit, an AD sampling circuit, a control module, a first DA digital-to-analog converter, a second DA digital-to-analog converter, and a signal adder. The output end of the signal adder is connected to the auxiliary winding, the output end of the receiving amplifier circuit is connected to the input end of the first multiplier and the input end of the second multiplier, and the carrier signal generator is divided into a first DA digital-to-analog converter and a second DA digital-to-analog converter. The first multiplier is respectively connected to the input end of the first multiplier and the input end of the second multiplier, the output end of the first multiplier is connected to the input end of the first low-pass filter amplifier circuit, the output end of the first low-pass filter amplifier circuit is connected to the input end of the AD sampling circuit, the output end of the second multiplier is connected to the input end of the second low-pass filter amplifier circuit, the output end of the second low-pass filter amplifier circuit is connected to the input end of the AD sampling circuit, the output end of the AD sampling circuit is connected to the control module, the control module is controlled and connected to the first DA digital-to-analog converter and the second DA digital-to-analog converter, and the output end of the first DA digital-to-analog converter and the output end of the second DA digital-to-analog converter are connected to the signal adder.

[0032] The carrier signal input to the first multiplier by the carrier signal generator is a first carrier signal, the carrier signal input to the second multiplier by the carrier signal generator is a second carrier signal, and the first carrier signal is orthogonal to the second carrier signal.

[0033] The AD sampling circuit is used to receive a first balanced signal after the balanced signal is multiplied, filtered and amplified by the first carrier signal, and a second balanced signal after the balanced signal is multiplied, filtered and amplified by the second carrier signal, and to sample the first balanced signal and the second balanced signal to output a first balanced digital signal and a second balanced digital signal.

[0034] The first balanced digital signal and the second balanced digital signal output by the AD sampling circuit contain amplitude information and phase information of the balanced signals.

[0035] The control module includes a storage unit.

[0036] The storage unit is used for storing the first balanced digital signal and the second balanced digital signal output by the AD sampling circuit.

[0037] The control module is used to perform the following processes:

[0038] Receiving in real time a first balanced digital signal and a second balanced digital signal output by an AD sampling circuit;

[0039] extracting balanced signal amplitudes from the first balanced digital signal and the second balanced digital signal;

[0040] Determine whether the amplitude of the balanced signal is greater than a first threshold value. If so, start timing. If the amplitude of the balanced signal is less than or equal to the first threshold value during the timing stage, the timing is reset to zero. If the timing duration is greater than a third threshold value, control the first DA digital-to-analog converter and the second DA digital-to-analog converter to output a first reconstructed analog signal and a second reconstructed analog signal respectively. The amplitude and phase of the reconstructed analog signal generated by superimposing the first reconstructed analog signal and the second reconstructed analog signal are the same as those of the balanced signal.

[0041] If the amplitude of the balanced signal is less than or equal to the first threshold, it is determined whether the amplitude of the balanced signal is greater than the second threshold. If it is greater, the timing is started. If the balanced signal is less than or equal to the second threshold during the timing stage, the timing is reset to zero. If the timing duration is greater than the third threshold, the first DA digital-to-analog converter and the second DA digital-to-analog converter are controlled to output the third reconstructed analog signal and the fourth reconstructed analog signal at time intervals equal to the first step according to the reconstructed analog signal output at the previous moment, until the amplitudes of the output third reconstructed analog signal and the fourth reconstructed analog signal are equal to the amplitude of the balanced signal.

[0042] The control module also includes the following execution process: if the amplitude of the balance signal is greater than the first threshold, the metal detector is controlled to stop detection.

[0043] The first threshold is greater than the second threshold.

[0044] The signal adder is used to superimpose the reconstructed analog signals output by the first DA digital-to-analog converter and the second DA digital-to-analog converter, and output the reconstructed analog signal. The auxiliary winding is used to receive the reconstructed analog signal output by the signal adder, inject the reconstructed analog signal into the receiving transformer, and subtract it from the balanced signal.

[0045] The implementation principle of this embodiment is as follows:

[0046] The solution of the present invention generates a reconstructed analog signal by processing the balanced signal Bal, and the reconstructed analog signal is sent to the auxiliary winding of the receiving transformer to offset the balanced signal, so that the balance is at a smaller value.

[0047] The balanced signal Bal is multiplied with a pair of orthogonal carrier signals to obtain CHX' and CHY', which are processed by a low-pass filter amplifier circuit to obtain two DC quantities CHX and CHY containing the characteristic information (amplitude and phase) of the balanced signal. After AD sampling, CHX and CHY are sent to the control module, and then the control module controls the output of two DA digital-to-analog converters according to the two DC quantities CHX and CHY to obtain two reconstructed analog signals, which are superimposed to obtain the reconstructed analog signal Bal'.

[0048] The relationship between the reproduced analog signal Bal′ and the balanced signal Bal is as follows:

[0049] The carrier signal generator generates a pair of orthogonal carrier signals:

[0050] Car0°=C·cos wt

[0051] Car90°=C·sin wt

[0052] The balanced signal is:

[0053] Bal=A·cos(wt+α)

[0054] Where α is the phase difference between the balanced signal and the carrier signal Car0°, and A is the amplitude of the balanced signal Bal;

[0055]

[0056]

[0057] So the reproduced analog signal Bal′

[0058] Bal′=(CHX×Car0°)+(CHY×Car90°)

[0059] =Mcosα×Ccos wt-Msinα×sin wt

[0060] =MC×Cos(wt+α)=P·cos(wt+α)

[0061] When the amplitude A of the balanced signal Bal increases, the amplitude P of the reproduced analog signal Bal′ will also increase synchronously. By offsetting the reproduced analog signal Bal′, the balanced signal Bal can be kept within a normal range.

[0062] This embodiment also provides a balance signal adjustment method for a metal detector, which adopts a method combining fast adjustment and slow adjustment. When the balance Bal does not exceed the threshold, the slow adjustment is used to slowly reduce the balance; when the balance Bal exceeds the threshold, the fast adjustment is used to quickly reduce the balance. Specifically:

[0063] After receiving CHX and CHY, the control module determines whether the amplitude of the balanced signal is greater than the first threshold. If so, the timing starts. If the duration of the amplitude of the balanced signal being greater than the first threshold is greater than or equal to the third threshold, the amplitude of the time balanced signal is too large, indicating that the symmetry of the receiving coil is significantly reduced, and the ability to suppress external differential mode interference is reduced. At this time, the control module needs to make rapid adjustments. The control module controls the two DA digital-to-analog converters to output two reconstructed analog signals, CHX×Car0° and CHY×Car90°, respectively. The two reconstructed analog signals are superimposed through a signal adder to obtain a reconstructed analog signal Bal′. The amplitude and phase of the reconstructed analog signal Bal′ are the same as those of the balanced signal Bal. Then the reconstructed analog signal Bal′ is input into the auxiliary winding of the receiving transformer to adjust the balanced signal. In the process of rapid adjustment, the control module controls the metal detector to stop detecting because the balanced signal at this time is The signal changes too much and the metal detector cannot work normally. If the amplitude of the balance signal is greater than the first threshold and the duration is less than the third threshold, it means that this is a balance signal change caused by metal detection, so there is no need to adjust the balance signal. If the amplitude of the balance signal is greater than the second threshold and less than the first threshold, the timing starts. If the amplitude of the balance signal is greater than the second threshold and less than the first threshold for a duration greater than or equal to the third threshold, it means that the balance signal is too large at this time. However, because the balance signal is not greater than the first threshold, we use slow adjustment to adjust the balance signal. The slow adjustment is to increase the fixed amplitude of the remade analog signal at regular intervals based on the last remade analog signal until the balance signal amplitude is within the normal range. If the amplitude of the balance signal is greater than the second threshold and less than the first threshold for a duration less than the third threshold, it means that this is a balance signal change caused by metal detection, so there is no need to adjust the balance signal.

[0064] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.

[0065] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A balanced signal adjustment system for a metal detector, characterized in that: The invention comprises a receiving coil, a receiving transformer, a receiving amplifier circuit, and a signal reproducing circuit. The receiving transformer comprises an auxiliary winding. The signal reproducing circuit comprises a carrier signal generator, a first multiplier (1), a second multiplier (2), a first low-pass filter amplifier circuit (3), a second low-pass filter amplifier circuit (4), an AD sampling circuit, a control module, a first DA digital-to-analog converter (5), a second DA digital-to-analog converter (6), and a signal adder (7). The output end of the signal adder (7) is connected to the auxiliary winding. The output end of the receiving amplifier circuit is connected to the input end of the first multiplier (1) and the input end of the second multiplier (2). The carrier signal generator is connected to the input end of the first multiplier (1) and the input end of the second multiplier (2). The first multiplier (1) is connected to an input end of a first low-pass filter amplifier circuit (3), the output end of the first low-pass filter amplifier circuit (3) is connected to an input end of an AD sampling circuit, the output end of the second multiplier (2) is connected to an input end of a second low-pass filter amplifier circuit (4), the output end of the second low-pass filter amplifier circuit (4) is connected to an input end of an AD sampling circuit, the output end of the AD sampling circuit is connected to a control module, the control module is controlled and connected to a first DA digital-to-analog converter (5) and a second DA digital-to-analog converter (6), and the output end of the first DA digital-to-analog converter (5) and the output end of the second DA digital-to-analog converter (6) are connected to a signal adder (7).

2. A metal detector balance signal adjustment system according to claim 1, characterized in that: The carrier signal inputted by the carrier signal generator to the first multiplier (1) is a first carrier signal, and the carrier signal inputted by the carrier signal generator to the second multiplier (2) is a second carrier signal. The first carrier signal is orthogonal to the second carrier signal.

3. A metal detector balance signal adjustment system according to claim 1 or 2, characterized in that: The AD sampling circuit is used to receive a first balanced signal after the balanced signal and the first carrier signal are multiplied, filtered and amplified, and a second balanced signal after the balanced signal and the second carrier signal are multiplied, filtered and amplified, and to sample the first balanced signal and the second balanced signal to output a first balanced digital signal and a second balanced digital signal.

4. A metal detector balance signal adjustment system according to claim 3, characterized in that: The first balanced digital signal and the second balanced digital signal output by the AD sampling circuit contain amplitude information and phase information of the balanced signals.

5. The balanced signal adjustment system for a metal detector according to claim 1, characterized in that: The control module includes a storage unit.

6. A metal detector balance signal adjustment system according to claim 5, characterized in that: The storage unit is used to store a first balanced digital signal and a second balanced digital signal output by the AD sampling circuit.

7. The balanced signal adjustment system for a metal detector according to claim 1, characterized in that: The control module is used to perform the following process: Receiving in real time a first balanced digital signal and a second balanced digital signal output by an AD sampling circuit; extracting balanced signal amplitudes from the first balanced digital signal and the second balanced digital signal; Determine whether the amplitude of the balanced signal is greater than a first threshold value, if so, start timing, if the amplitude of the balanced signal is less than or equal to the first threshold value during the timing stage, the timing is reset to zero, if the timing duration is greater than a third threshold value, control the first DA digital-to-analog converter (5) and the second DA digital-to-analog converter (6) to output a first reconstructed analog signal and a second reconstructed analog signal respectively, the amplitude and phase of the reconstructed analog signal generated by superposition of the first reconstructed analog signal and the second reconstructed analog signal being the same as the balanced signal; If the amplitude of the balanced signal is less than or equal to the first threshold, it is determined whether the amplitude of the balanced signal is greater than the second threshold. If it is greater, timing is started. If the balanced signal is less than or equal to the second threshold during the timing stage, the timing is reset to zero. If the timing duration is greater than the third threshold, the first DA digital-to-analog converter (5) and the second DA digital-to-analog converter (6) are controlled to output a third reconstructed analog signal and a fourth reconstructed analog signal at time intervals equal to the first step length according to the reconstructed analog signal output at the previous moment, until the amplitudes of the output third reconstructed analog signal and the fourth reconstructed analog signal are equal to the amplitude of the balanced signal.

8. A metal detector balance signal adjustment system according to claim 7, characterized in that: The control module further includes the following execution process: if the amplitude of the balance signal is greater than the first threshold and the duration is greater than the third threshold, the metal detector is controlled to stop detection.

9. A metal detector balance signal adjustment system according to claim 7, characterized in that: The first threshold is greater than the second threshold.

10. The balanced signal adjustment system for a metal detector according to claim 1, characterized in that: The signal adder (7) is used to superimpose the reconstructed analog signals output by the first DA digital-to-analog converter (5) and the second DA digital-to-analog converter (6), and output the reconstructed analog signal; the auxiliary winding is used to receive the reconstructed analog signal output by the signal adder (7), inject the reconstructed analog signal into the receiving transformer, and subtract it from the balanced signal.

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