Phase compensation method and circuit for detection system of metal detector

Abstract

The invention relates to a phase compensation method and circuit for a detection system of a metal detector. The method comprises the following steps: generating a first carrier signal and a second carrier signal which has the same amplitude as the first carrier signal and has a 90-degree phase difference with the first carrier signal; acquiring a balanced voltage signal of a detection system of the metal detector in real time; the balanced voltage signal and the first carrier signal are input into a first channel, the balanced voltage signal and the second carrier signal are input into a second channel, a first processing signal and a second processing signal are obtained, and the first channel and the second channel sequentially carry out signal demodulation, signal filtering and AD sampling operation on the two input signals respectively; solving a balanced voltage signal phase based on the first and second processed signals; and adjusting the phase of the sine emission carrier signal of the detection system of the metal detector in real time based on the phase difference between the balanced voltage signal phases at the current moment and the last moment. Compared with the prior art, the problem of emission phase drift caused by temperature drift in the operation process of the metal detector is solved, and the detection precision can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal detection, and in particular to a phase compensation method and circuit for a metal detector detection system. Background Art

[0002] During the operation of the metal detector, the emission phase is one of the key detection parameters of the entire system, and it plays a very important role in suppressing the product signal to improve the metal detection performance. However, in the traditional system solution, the coil module, power circuit, analog demodulation circuit, etc. will inevitably have temperature drift problems during the operation of the product, which will cause the emission phase to drift, resulting in a decrease in the detection accuracy of the metal detector. Summary of the invention

[0003] The purpose of the present invention is to provide a phase compensation method and circuit for a metal detector detection system, which realizes phase compensation by calculating the phase and amplitude of a balanced signal in real time for phase tracking, thereby improving detection accuracy.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A phase compensation method for a metal detector detection system, wherein the metal detector detection system drives a transmitting coil with a sinusoidal transmitting carrier signal and performs metal detection by acquiring a balanced voltage signal output by a receiving coil, the method comprising the following steps:

[0006] Generate a first carrier signal and a second carrier signal, wherein the first carrier signal and the second carrier signal have the same amplitude and a 90 degree phase difference, and the balanced voltage signal, the first carrier signal and the second carrier signal have the same frequency;

[0007] Real-time acquisition of the balanced voltage signal output by the receiving coil of the metal detector detection system;

[0008] The balanced voltage signal and the first carrier signal are input into the first channel together, and a first processed signal is output; the balanced voltage signal and the second carrier signal are input into the second channel together, and a second processed signal is output; the first channel and the second channel respectively perform signal demodulation and signal filtering operations on the two input signals in sequence;

[0009] Determining a balanced voltage signal phase based on the first processed signal and the second processed signal;

[0010] The phase of the sinusoidal transmission carrier signal of the metal detector detection system is adjusted in real time based on the phase difference between the balanced voltage signal phase at the current moment and the previous moment.

[0011] The signal demodulation is implemented based on an analog multiplication circuit, and a mixed signal is obtained by multiplying two input signals. The mixed signal consists of a DC bias signal and a double frequency signal, and the frequency of the double frequency signal is twice that of the sinusoidal transmission carrier signal.

[0012] The signal filtering uses low-pass filtering to filter out the double frequency signal in the mixed signal. The filtered DC bias signal reflects the emission phase drift caused by the temperature drift of the metal detector detection system, and its magnitude is affected by the amplitude and phase of the balanced voltage signal and the amplitude of the first / second carrier signal.

[0013] A phase compensation circuit of a metal detector detection system, wherein the metal detector detection system drives a transmitting coil with a sinusoidal transmitting carrier signal and performs metal detection by acquiring a balanced voltage signal output by a receiving coil, wherein the phase compensation circuit comprises a sinusoidal carrier signal source, a dual-channel demodulation circuit and a digital signal processing circuit.

[0014] The sinusoidal carrier signal source is used to generate a first carrier signal and a second carrier signal, wherein the first carrier signal and the second carrier signal have the same amplitude and a 90-degree phase difference, and the balanced voltage signal, the first carrier signal and the second carrier signal have the same frequency;

[0015] The dual-channel demodulation circuit includes two channels, wherein the first channel takes the balanced voltage signal and the first carrier signal output by the receiving coil of the metal detector detection system acquired in real time as input and outputs a first processed signal, and the second channel takes the balanced voltage signal and the second carrier signal as input and outputs a second processed signal, and the first channel and the second channel respectively include a signal demodulation circuit and a signal filtering circuit;

[0016] The digital signal processing circuit includes an AD conversion circuit, a digital signal operation circuit based on FPGA, a digital signal generator and a DA conversion circuit. The AD conversion circuit converts the analog signal output by the dual-channel demodulation circuit into a digital signal, solves the phase of the balanced voltage signal based on the digital signal using the digital signal operation circuit, and calculates the phase difference between the balanced voltage signal phase at the current moment and the previous moment. The digital signal generator is used to generate an adjustment signal according to the phase difference, and the adjustment signal is converted into an analog signal by the DA conversion circuit and is used to adjust the phase of the sinusoidal transmission carrier signal of the metal detector detection system in real time.

[0017] The metal foreign body detector detection system includes a sinusoidal transmitting carrier signal source, a transmitting resonant power circuit, a coil module and a receiving circuit. The coil module includes a transmitting coil and two receiving coils. The sinusoidal transmitting carrier signal source provides a sinusoidal transmitting carrier signal for the transmitting resonant power circuit. The sinusoidal transmitting carrier signal is power-amplified by the transmitting resonant power circuit and then input into the transmitting coil of the coil module. The output signal of the receiving coil in the coil module is received by the receiving circuit to obtain a balanced voltage signal.

[0018] The sinusoidal transmitting carrier signal source is realized by a digital signal generator of FPGA, and the digital signal output by the digital signal generator is converted into an analog signal through a DA conversion circuit to obtain a sinusoidal transmitting carrier signal.

[0019] The signal demodulation circuit adopts an analog multiplication circuit to multiply two input signals to obtain a mixed signal, wherein the mixed signal is composed of a DC bias signal and a double frequency signal, and the frequency of the double frequency signal is twice that of the sinusoidal transmission carrier signal.

[0020] The signal filtering circuit uses a low-pass filtering circuit to filter out the double frequency signal in the mixed signal. The filtered DC bias signal reflects the emission phase drift caused by the temperature drift of the metal detector detection system, and its magnitude is affected by the amplitude and phase of the balanced voltage signal and the amplitude of the first / second carrier signal.

[0021] The AD conversion chip used in the AD conversion circuit with different precision is selected according to the size of the DC bias signal. The smaller the DC bias signal, the higher the precision of the corresponding AD conversion chip.

[0022] The size of the DC bias signal is adjusted by adjusting the amplitude of the first / second carrier signal, and the AD conversion chip used by the AD conversion circuit with different precision is selected according to the size of the adjusted DC bias signal. The smaller the DC bias signal, the higher the precision of the corresponding AD conversion chip.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention obtains a DC signal that can reflect the amplitude and phase of the balanced voltage signal by demodulating and filtering the balanced voltage signal output by the metal detector detection system. The phase difference between the two moments can be calculated by acquiring the real-time signal in real time and comparing it with the signal at a historical moment, so as to reflect the phase drift generated by the system during operation. Based on the phase, the system input sinusoidal carrier is precisely controlled to compensate for the phase drift, thereby improving the detection accuracy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1It is a schematic diagram of the phase compensation circuit structure of the present invention;

[0026] Figure 2 A schematic diagram of the signal processing process of each channel in the dual-channel demodulation circuit of the present invention;

[0027] Figure 3 The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0028] 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.

[0029] Example 1

[0030] like Figure 1 As shown, the metal detector detection system drives the transmitting coil with a sinusoidal transmitting carrier signal, and performs metal detection by obtaining the balanced voltage signal output by the receiving coil, including a sinusoidal transmitting carrier signal source, a transmitting resonant power circuit, a coil module and a receiving circuit.

[0031] (1) Sinusoidal transmission carrier signal source

[0032] The sinusoidal transmitting carrier signal source provides a sinusoidal transmitting carrier signal for the transmitting resonant power circuit, which can be realized by the digital signal generator (DDS) of FPGA, and the digital signal output by the digital signal generator is converted into an analog signal through the DA conversion chip to obtain a sinusoidal transmitting carrier signal C with digitally adjustable phase and amplitude. tr .

[0033] (2) Transmitting resonant power circuit

[0034] The transmitting resonant power circuit is the transmitting power circuit of the metal detector. It cooperates with the transmitting coil to amplify the power through LC resonance, thereby generating an alternating magnetic field.

[0035] (3) Coil module

[0036] The coil module includes a transmitting coil and two receiving coils, wherein a sinusoidal transmitting carrier signal is input into the transmitting coil of the coil module after being power-amplified by a transmitting resonant power circuit, and an output signal of the receiving coil in the coil module is received by a receiving circuit.

[0037] (4) Receiving circuit

[0038] The receiving circuit is used to process the receiving voltage difference of the receiving coil and generate a balanced voltage signal S bal .

[0039] Based on the above metal detector detection system, the temperature drift problem is mainly caused by the coil module, the transmitting resonant power circuit and the analog circuit part of the receiving circuit, which ultimately acts on the balanced voltage signal S output by the receiving circuit. bal That is, for the phase of the adjusted transmission carrier, due to the existence of the above-mentioned temperature drift problem of the analog part components, it will inevitably lead to the change of the signal after the demodulation of the balanced voltage signal.

[0040] This embodiment provides a phase compensation circuit for a metal detector detection system. Figure 1 As shown, it includes a sinusoidal carrier signal source, a dual-channel demodulation circuit and a digital signal processing circuit.

[0041] (5) Sinusoidal carrier signal source

[0042] The sinusoidal carrier signal source is used to generate the first carrier signal C de1 and the second carrier signal C de2 , providing a basic sinusoidal carrier for the dual-channel demodulation circuit. The first carrier signal and the second carrier signal have the same amplitude and a 90-degree phase difference, and the balanced voltage signal, the first carrier signal and the second carrier signal have the same frequency; that is:

[0043] The balanced voltage signal received by the receiving circuit is expressed as:

[0044] The first carrier signal is represented by: C de1 = Bcos(wt);

[0045] The second carrier signal is expressed as: C de2 =Bcos(wt+90°)=-Bsin(wt).

[0046] (6) Dual-channel demodulation circuit

[0047] The dual-channel demodulation circuit includes two channels, wherein the first channel is a balanced voltage signal S output by the receiving coil of the metal detector detection system obtained in real time. bal and the first carrier signal C de1 The second channel uses a balanced voltage signal S bal With the second carrier signal C de2 The second processed signal D2 is input and output.

[0048] like Figure 2 As shown, the first channel and the second channel include a signal demodulation circuit and a signal filtering circuit respectively.

[0049] The signal demodulation circuit adopts an analog multiplication circuit to multiply the two input signals to obtain a mixed signal. The mixed signal consists of a DC bias signal and a doubled frequency signal. The frequency of the doubled frequency signal is twice the frequency of the sinusoidal transmission carrier signal / balanced voltage signal / first carrier signal / second carrier signal.

[0050] The signal filtering circuit uses a low-pass filtering circuit to filter out the double frequency signal in the mixed signal. The filtered DC bias signal reflects the emission phase drift caused by the temperature drift of the metal detector detection system, and its magnitude is affected by the amplitude and phase of the balanced voltage signal and the amplitude of the first / second carrier signal.

[0051] Then, the signal in the first channel is multiplied by the analog multiplication circuit to obtain:

[0052]

[0053] After passing through the low-pass filter circuit, the signal components corresponding to sin(2wt) and cos(2wt) are filtered out to obtain the DC bias signal:

[0054]

[0055] This DC bias signal represents Phase change due to temperature.

[0056] For any moment Balanced voltage signal, filtered The peak-to-peak value of the DC quantity A and A is an unknown variable, and B is a known controllable variable, so two DC quantities are needed to calculate A and In this embodiment, this can be achieved by using signals output from two channels.

[0057] Based on the above derivation, it is necessary to calculate the real-time balanced phase to achieve phase tracking. In order to calculate the phase in real time, it is necessary to cooperate with the second channel. Referring to the above derivation process, the DC bias signal obtained by the input signal of the second channel after passing through the analog multiplication circuit and the low-pass filter circuit is:

[0058]

[0059] (7) Digital signal processing circuit

[0060] The digital signal processing circuit includes an AD conversion circuit, a digital signal operation circuit based on FPGA, a digital signal generator and a DA conversion circuit. The AD conversion circuit converts the analog signals D1 and D2 output by the dual-channel demodulation circuit into digital signals, and uses the digital signal operation circuit to solve the phase of the balanced voltage signal based on the digital signal, and calculates the phase difference between the current moment and the previous moment.

[0061] Combining equations (1) and (2) above, we can obtain:

[0062]

[0063] Then we can solve A and

[0064] Assume that the phase of the balanced voltage signal corresponding to time t1 is The phase of the balanced voltage signal corresponding to the current moment t2 is The amplitude A of the balanced voltage signal and the phase at two moments can be calculated by the above formula (3): and The phase difference The phase difference reflects the transmission phase drift caused by the temperature drift in the interval between time t1 and time t2. The phase difference is fed back to the sinusoidal transmission carrier signal source to adjust the phase of the transmission carrier signal for phase compensation.

[0065] The digital signal processing circuit can realize phase calculation tracking and phase compensation while realizing signal detection processing. Specifically, for the processing of metal detection signals, the digital signal processing circuit can only digitally process the signal D1 or D2. Because the product or metal will affect the balanced voltage signal during real-time detection, phase compensation cannot be performed when the metal detector performs product detection (when a product passes through the detection system). Within the time range when no product detection is performed, phase calculation and tracking are achieved through D1 and D2. In this embodiment, in order to identify whether product detection is being performed, a photoelectric sensor is added at the entrance of the probe to determine whether a product has entered the probe.

[0066] According to equation (1) or (2), it can be found that the change of the DC bias signal is controlled by the amplitude B of the carrier signal, and the amplitude A of the balanced signal is also affected by the temperature drift. Therefore, while monitoring the phase in real time, it is also necessary to calculate the accurate value of the amplitude A in real time.

[0067] In addition, B can be used to adjust the value brought by the phase change, which is also beneficial for the accuracy selection of the AD conversion chip used in the AD conversion circuit. This embodiment selects AD conversion chips of different precisions according to the size of the DC bias signal. The smaller the DC bias signal, the higher the precision of the corresponding AD conversion chip. When the DC bias signal is too small, it is difficult to match a high-precision AD conversion chip, and the use of a high-precision AD conversion chip will also increase the cost. At this time, the size of the DC bias signal can be adjusted by adjusting the amplitude B of the first / second carrier signal, and a lower-precision AD conversion chip can be selected according to the size of the adjusted DC bias signal, which can also achieve the same detection accuracy.

[0068] Example 2

[0069] This embodiment provides a phase compensation method for a metal detector detection system, which is implemented based on the phase compensation circuit described in Embodiment 1. Figure 3 As shown, the method comprises the following steps:

[0070] S1, generate the first carrier signal C de1 and the second carrier signal C de2 ;

[0071] S2, real-time acquisition of the balanced voltage signal S output by the receiving coil of the metal detector detection system bal ;

[0072] S3, the balanced voltage signal S bal With the first carrier signal C de1 The first channel is inputted together, and the first processed signal D1 is outputted, and the balanced voltage signal S bal With the second carrier signal C de2 The second channel is inputted together and a second processed signal D2 is outputted. The first channel and the second channel respectively perform signal demodulation and signal filtering operations on the two input signals in sequence;

[0073] S4, solving the phase of the balanced voltage signal based on the first processed signal and the second processed signal

[0074] S5, based on the phase difference between the current and previous balanced voltage signal phases Real-time adjustment of the phase of the sinusoidal transmission carrier signal of the metal detector detection system.

[0075] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A phase compensation method for a metal detector detection system, wherein the metal detector detection system drives a transmitting coil with a sinusoidal transmitting carrier signal and performs metal detection by obtaining a balanced voltage signal output by a receiving coil, characterized in that: The method comprises the following steps: Generate a first carrier signal and a second carrier signal, wherein the first carrier signal and the second carrier signal have the same amplitude and a 90 degree phase difference, and the balanced voltage signal, the first carrier signal and the second carrier signal have the same frequency; Real-time acquisition of the balanced voltage signal output by the receiving coil of the metal detector detection system; The balanced voltage signal and the first carrier signal are input into the first channel together, and a first processed signal is output; the balanced voltage signal and the second carrier signal are input into the second channel together, and a second processed signal is output; the first channel and the second channel respectively perform signal demodulation and signal filtering operations on the two input signals in sequence; Determining a balanced voltage signal phase based on the first processed signal and the second processed signal; The phase of the sinusoidal transmission carrier signal of the metal detector detection system is adjusted in real time based on the phase difference between the balanced voltage signal phase at the current moment and the previous moment.

2. The phase compensation method of a metal detector detection system according to claim 1, characterized in that: The signal demodulation is implemented based on an analog multiplication circuit, and a mixed signal is obtained by multiplying two input signals. The mixed signal consists of a DC bias signal and a double frequency signal, and the frequency of the double frequency signal is twice that of the sinusoidal transmission carrier signal.

3. The phase compensation method of a metal detector detection system according to claim 2, characterized in that: The signal filtering uses low-pass filtering to filter out the double frequency signal in the mixed signal. The filtered DC bias signal reflects the emission phase drift caused by the temperature drift of the metal detector detection system, and its magnitude is affected by the amplitude and phase of the balanced voltage signal and the amplitude of the first / second carrier signal.

4. A phase compensation circuit of a metal detector detection system, wherein the metal detector detection system drives a transmitting coil with a sinusoidal transmitting carrier signal and performs metal detection by obtaining a balanced voltage signal output by a receiving coil, characterized in that: The phase compensation circuit includes a sinusoidal carrier signal source, a dual-channel demodulation circuit and a digital signal processing circuit. The sinusoidal carrier signal source is used to generate a first carrier signal and a second carrier signal, wherein the first carrier signal and the second carrier signal have the same amplitude and a 90-degree phase difference, and the balanced voltage signal, the first carrier signal and the second carrier signal have the same frequency; The dual-channel demodulation circuit includes two channels, wherein the first channel takes the balanced voltage signal and the first carrier signal output by the receiving coil of the metal detector detection system acquired in real time as input and outputs a first processed signal, and the second channel takes the balanced voltage signal and the second carrier signal as input and outputs a second processed signal, and the first channel and the second channel respectively include a signal demodulation circuit and a signal filtering circuit; The digital signal processing circuit includes an AD conversion circuit, a digital signal operation circuit based on FPGA, a digital signal generator and a DA conversion circuit. The AD conversion circuit converts the analog signal output by the dual-channel demodulation circuit into a digital signal, solves the phase of the balanced voltage signal based on the digital signal using the digital signal operation circuit, and calculates the phase difference between the balanced voltage signal phase at the current moment and the previous moment. The digital signal generator is used to generate an adjustment signal according to the phase difference, and the adjustment signal is converted into an analog signal by the DA conversion circuit and is used to adjust the phase of the sinusoidal transmission carrier signal of the metal detector detection system in real time.

5. The phase compensation circuit of the metal detector detection system according to claim 4, characterized in that: The metal foreign body detector detection system includes a sinusoidal transmitting carrier signal source, a transmitting resonant power circuit, a coil module and a receiving circuit. The coil module includes a transmitting coil and two receiving coils. The sinusoidal transmitting carrier signal source provides a sinusoidal transmitting carrier signal for the transmitting resonant power circuit. The sinusoidal transmitting carrier signal is power-amplified by the transmitting resonant power circuit and then input into the transmitting coil of the coil module. The output signal of the receiving coil in the coil module is received by the receiving circuit to obtain a balanced voltage signal.

6. The phase compensation circuit of the metal detector detection system according to claim 5, characterized in that: The sinusoidal transmitting carrier signal source is realized by a digital signal generator of FPGA, and the digital signal output by the digital signal generator is converted into an analog signal through a DA conversion circuit to obtain a sinusoidal transmitting carrier signal.

7. The phase compensation circuit of a metal detector detection system according to claim 4, characterized in that: The signal demodulation circuit adopts an analog multiplication circuit to multiply two input signals to obtain a mixed signal, wherein the mixed signal is composed of a DC bias signal and a double frequency signal, and the frequency of the double frequency signal is twice that of the sinusoidal transmission carrier signal.

8. The phase compensation circuit of the metal detector detection system according to claim 7, characterized in that: The signal filtering circuit uses a low-pass filtering circuit to filter out the double frequency signal in the mixed signal. The filtered DC bias signal reflects the emission phase drift caused by the temperature drift of the metal detector detection system, and its magnitude is affected by the amplitude and phase of the balanced voltage signal and the amplitude of the first / second carrier signal.

9. The phase compensation circuit of the metal detector detection system according to claim 8, characterized in that: The AD conversion chip used in the AD conversion circuit with different precision is selected according to the size of the DC bias signal. The smaller the DC bias signal, the higher the precision of the corresponding AD conversion chip.

10. The phase compensation circuit of the metal detector detection system according to claim 8, characterized in that: The size of the DC bias signal is adjusted by adjusting the amplitude of the first / second carrier signal, and the AD conversion chip used by the AD conversion circuit with different precision is selected according to the size of the adjusted DC bias signal. The smaller the DC bias signal, the higher the precision of the corresponding AD conversion chip.

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