Ferromagnetic content measuring circuit based on DDS technology

Abstract

The invention discloses a ferromagnetic content measuring circuit based on a DDS technology. The ferromagnetic content measuring circuit comprises a DDS signal source, a first coil, a second coil and a processor. The DDS signal source is used for outputting a first sine wave signal and a second sine wave signal, and the first sine wave signal and the second sine wave signal form a group of differential signals; the input ends of the first coil and the second coil respectively receive a first sine wave signal and a second sine wave signal, and the output ends are electrically connected to form a first connection node; the first coil or the second coil is used for placing a to-be-tested sample so as to enable the first connection node to form a differential change signal; and the processor determines the ferromagnetic content of the to-be-detected sample according to the differential change signal. By using the DDS signal source, the accuracy of a test result is improved, measurement errors caused by inaccurate differential signals are reduced, meanwhile, environmental interference can be effectively eliminated, the detection sensitivity and the anti-interference capability of the test circuit are improved, and by adopting standard electronic elements, the detection cost is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of ferromagnetic content detection technology, and in particular to a ferromagnetic content measurement circuit based on DDS technology. Background Technology

[0002] In mechanical power systems, the wear condition of ferrous components directly affects the operational reliability and service life of the equipment. Because large instruments generate wear particles during operation, these particles enter the lubricating oil, making the lubricating oil a crucial carrier reflecting the mechanical wear condition. By monitoring the content of ferromagnetic abrasive particles in the lubricating oil, the degree of equipment wear can be assessed, thereby predicting potential failures and guiding maintenance decisions.

[0003] Currently, the detection of ferromagnetic abrasive particles in lubricating oil mainly relies on laboratory analytical methods, such as ferrography, spectroscopic analysis, and particle counting. Ferrography separates abrasive particles using a magnetic field and observes their morphology, but it has a long testing cycle, is complex to operate, and requires highly skilled personnel. Spectroscopic analysis can accurately determine the content of multiple elements, but the equipment is bulky and expensive, making rapid on-site testing difficult. While particle counters can count the number and size of particles, they cannot distinguish ferromagnetic particles from other impurities, resulting in significant limitations in the detection results. Summary of the Invention

[0004] This invention provides a ferromagnetic content measurement circuit based on DDS technology, which improves the detection sensitivity and anti-interference ability of the test circuit and reduces the detection cost.

[0005] This invention provides a ferromagnetic content measurement circuit based on DDS technology, comprising:

[0006] The DDS signal source includes a first output terminal and a second output terminal. The first output terminal is used to output a first sine wave signal, and the second output terminal is used to output a second sine wave signal. The first sine wave signal and the second sine wave signal constitute a set of differential signals.

[0007] A first coil and a second coil are arranged in the same plane; the input terminal of the first coil receives the first sine wave signal, and the input terminal of the second coil receives the second sine wave signal; the output terminals of the first coil and the second coil are electrically connected to form a first connection node; the first coil or the second coil is used to place the sample to be tested so that the first connection node forms a differential change signal;

[0008] A processor is used to determine the ferromagnetic content of the sample to be tested based on the differential change signal.

[0009] Optionally, the measurement circuit further includes a DDS amplifier circuit;

[0010] The input terminal of the DDS amplifier circuit is electrically connected to the first output terminal and the second output terminal, respectively, and the output terminal is electrically connected to the input terminal of the first coil and the input terminal of the second coil, respectively.

[0011] The DDS amplifier circuit is used to amplify the first sine wave signal and the second sine wave signal, respectively.

[0012] Optionally, the DDS amplifier circuit includes a first amplifier and a second amplifier;

[0013] The non-inverting input terminal of the first amplifier is electrically connected to the first output terminal, and the output terminal is electrically connected to the input terminal of the first coil; the first amplifier is used to amplify the first sine wave signal.

[0014] The non-inverting input terminal of the second amplifier is electrically connected to the second output terminal, the inverting input terminal is electrically connected to the inverting input terminal of the first amplifier, and the output terminal is electrically connected to the input terminal of the second coil; the second amplifier is used to amplify the second sine wave signal.

[0015] Optionally, the DDS amplifier circuit further includes a DC bias circuit and a DC blocking circuit;

[0016] The DC bias circuit includes a first resistor and a second resistor, which are connected in series with a first power supply terminal and a ground terminal, and the first resistor and the second resistor are connected to form a second connection node; the second connection node is electrically connected to the non-inverting input terminal of the first amplifier and the non-inverting input terminal of the second amplifier, respectively.

[0017] The DC blocking circuit includes a first capacitor and a second capacitor; the first capacitor is connected in series between the output terminal of the first amplifier and the input terminal of the first coil; the second capacitor is connected in series between the output terminal of the second amplifier and the input terminal of the second coil.

[0018] Optionally, the measurement circuit further includes a differential signal amplifier circuit and an analog-to-digital converter unit;

[0019] The differential signal amplification circuit is electrically connected to the first connection node and is used to amplify the differential change signal to generate an amplified change signal.

[0020] The analog-to-digital conversion unit is electrically connected to the output terminal of the differential signal amplifier circuit, and is used to perform analog-to-digital conversion on the amplified changing signal to generate a digital changing signal;

[0021] The processor is used to determine the ferromagnetic content of the sample to be tested based on the digital change signal.

[0022] Optionally, the measurement circuit further includes a digital locator; the digital locator includes two input terminals and one output terminal;

[0023] The digital locator receives the first sine wave signal and the second sine wave signal at its two input terminals, respectively, and its output terminal is electrically connected to the differential signal amplifier circuit.

[0024] The digital positioner is used to adjust its own impedance to output a reference differential change signal; wherein the reference differential change signal is the same as the differential change signal formed when the first connection node has no sample to be tested in either the first coil or the second coil.

[0025] Optionally, the differential signal amplification circuit includes a third amplifier and a fourth amplifier;

[0026] The non-inverting input terminal of the third amplifier is electrically connected to the first connection node, the non-inverting input terminal of the fourth amplifier is electrically connected to the output terminal of the digital positioner, and the inverting input terminal of the third amplifier is electrically connected to the inverting input terminal of the fourth amplifier.

[0027] The third amplifier is used to amplify the differential change signal of the first connection node, and the fourth amplifier is used to amplify the reference differential change signal.

[0028] Optionally, the analog-to-digital conversion unit is a comparator, and the output terminals of the third amplifier and the fourth amplifier are respectively electrically connected to the two input terminals of the comparator;

[0029] The comparator is used to compare the differential change signal of the first connection node with the reference differential change signal to generate the digital change signal.

[0030] Optionally, the first coil and the second coil are disposed in at least one conductive line layer of the printed circuit board.

[0031] Optionally, the printed circuit board includes a metal layer cutout area, where both the first coil and the second coil are located, and no other conductive structures other than the first coil and the second coil are provided in each conductive line layer of the metal layer cutout area.

[0032] This invention generates a set of differential sinusoidal signals using a DDS signal source and inputs them into a first coil and a second coil. By detecting the signal changes at the first connection node formed at the output terminals of the first and second coils, the ferromagnetic content of the sample under test is determined. Using a DDS signal source to generate high-quality sinusoidal signals improves the accuracy of the test results and reduces measurement errors introduced by inaccurate differential signals. Furthermore, using differential signals effectively eliminates environmental interference, improving the detection sensitivity and anti-interference capability of the test circuit. Finally, by employing standard electronic components, the testing cost is effectively reduced. Attached Figure Description

[0033] Figure 1 A ferromagnetic content measurement circuit based on DDS technology is provided for embodiments of the present invention;

[0034] Figure 2 Another ferromagnetic content measurement circuit based on DDS technology is provided in this embodiment of the invention;

[0035] Figure 3 This is a schematic diagram of a printed circuit board with an induction coil wound according to an embodiment of the present invention. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0037] The terminology used in the embodiments of this invention is for the purpose of describing specific embodiments only and is not intended to limit the invention. It should be noted that directional terms such as "upper," "lower," "left," and "right" described in the embodiments of this invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this invention. Furthermore, in the context, it should be understood that when referring to an element being formed "on" or "below" another element, it can be formed not only directly on or below the other element, but also indirectly on or below it through intermediate elements. The terms "first," "second," etc., are used for descriptive purposes only and do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] The term "comprising" and its variations as used in this invention are open-ended, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment".

[0039] It should be noted that the concepts of "first" and "second" mentioned in this invention are only used to distinguish the corresponding contents and are not used to limit the order or interdependence.

[0040] It should be noted that the terms "a" and "a plurality of" used in this invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0041] Figure 1 A ferromagnetic content measurement circuit based on DDS technology is provided as an embodiment of the present invention, such as Figure 1 As shown, the measurement circuit includes a DDS signal source 10, a first coil 20, a second coil 21, and a processor 30. The DDS signal source 10 includes a first output terminal 101 and a second output terminal 102. The first output terminal 101 is used to output a first sine wave signal, and the second output terminal 102 is used to output a second sine wave signal. The first sine wave signal and the second sine wave signal constitute a set of differential signals. The first coil 20 and the second coil 21 are arranged in the same plane. The input terminal of the first coil 20 receives the first sine wave signal, and the input terminal of the second coil 21 receives the second sine wave signal. The output terminals of the first coil 20 and the second coil 21 are electrically connected to form a first connection node 22. The first coil 20 or the second coil 21 is used to place the sample to be tested so that the first connection node 22 forms a differential change signal. The processor 30 is used to determine the ferromagnetic content of the sample to be tested based on the differential change signal.

[0042] Specifically, refer to Figure 1 The DDS signal source 10 outputs a first sine wave signal at the first output terminal 101 and a second sine wave signal at the second output terminal 102. The first sine wave signal and the second sine wave signal constitute a set of differential signals, that is, the amplitude of the first sine wave signal and the second sine wave signal are equal and the phase is opposite. Therefore, if the first sine wave signal and the second sine wave signal are superimposed, a signal with an amplitude of 0 will be obtained.

[0043] Furthermore, using a DDS signal source to generate a sine wave has the advantages of low power consumption, high spectral quality, easy debugging, and high integration. If a discrete FPGA combined with a DAC is used to generate a sine wave, there are problems such as high power consumption, low spectral quality and moderate debugging difficulty, and low integration. If an analog PLL method is used, there are also problems such as high power consumption, complex debugging difficulty, and the need for a large number of components. Figure 2 Another ferromagnetic content measurement circuit based on DDS technology provided in this embodiment of the invention, such as Figure 2As shown, the DDS signal source 10 can be composed of an AD9838BCPZ main chip and external filter capacitors, wherein the AD9838 main chip can generate high-performance sine wave and triangular wave outputs. Exemplarily, in this embodiment, a microcontroller controls the AD9838BCPZ main chip to generate a set of differential 100kHz sine wave signals, which are output from pins 16 and 17 of the AD9838BCPZ main chip.

[0044] Further reference Figure 1 The first sine wave signal is input to the input terminal of the first coil 20, and the second sine wave signal is input to the input terminal of the second coil 21. Theoretically, when the characteristics of the first coil 20 and the second coil 21 are completely identical, the first sine wave signal and the second sine wave signal will still be a set of differential signals at the output terminals of the first coil 20 and the second coil 21 after passing through the first coil 20 and the second coil 21. That is, they will maintain the characteristics of equal amplitude and opposite phase. Therefore, when the output terminals of the first coil 20 and the second coil 21 are electrically connected to form the first connection node 22, a signal with an amplitude of 0 will be obtained at the first connection node 22.

[0045] Furthermore, if a sample to be tested is placed in the first coil 20 or the second coil 21, the magnetic field of the coil will change due to the ferromagnetic content in the sample. This will cause the characteristics of the coil with the sample to no longer be consistent with those of the other coil. Therefore, when the first sine wave signal is input to the input terminal of the first coil 20 and the second sine wave signal is input to the input terminal of the second coil 21, a differential change signal with a non-zero amplitude will be obtained at the first connection node 22.

[0046] Furthermore, the differential change signal is input into the processor 30. The processor 30 can determine the ferromagnetic content of the sample to be tested based on the amplitude change of the differential change signal. The higher the content of ferromagnetic material, the greater the change in magnetic field and the greater the voltage change.

[0047] This invention generates a set of differential sine wave signals using a DDS signal source and inputs them into a first coil and a second coil. By detecting the signal change at the first connection node formed at the output terminals of the first and second coils, the ferromagnetic content of the sample under test is determined. This invention improves the accuracy of test results by using a DDS signal source to generate high-quality sine wave signals, reducing measurement errors introduced by inaccurate differential signals. Furthermore, the use of differential signals effectively eliminates environmental interference, improving the detection sensitivity and anti-interference capability of the test circuit. Finally, the use of standard electronic components effectively reduces testing costs.

[0048] Optionally, refer to Figure 2The measurement circuit also includes a DDS amplifier circuit 40; the input terminal of the DDS amplifier circuit 40 is electrically connected to the first output terminal 101 and the second output terminal 102 respectively, and the output terminal is electrically connected to the input terminal of the first coil 20 and the input terminal of the second coil 21 respectively; the DDS amplifier circuit 40 is used to amplify the first sine wave signal and the second sine wave signal respectively.

[0049] Specifically, the DDS amplifier circuit 40 includes a third input terminal 401 and a fourth input terminal 402. A first sine wave signal generated by the DDS signal source is input to the third input terminal 401 of the DDS amplifier circuit through the first output terminal 101, and a second sine wave signal is input to the fourth input terminal 402 of the DDS amplifier circuit through the second output terminal 102. After being amplified to the same extent in the DDS amplifier circuit 40, the first and second sine wave signals are output to the first coil 20 and the second coil 21, respectively, through the output terminal of the DDS amplifier circuit 40. The DDS amplifier circuit 40 includes a third output terminal 403 and a fourth output terminal 404. The amplified first sine wave signal is output to the input terminal of the first coil 20 through the third output terminal 403, and the amplified second sine wave signal is output to the input terminal of the second coil 21 through the fourth output terminal 404.

[0050] In an alternative embodiment, reference continues. Figure 2 The DDS amplifier circuit 40 includes a first amplifier 41 and a second amplifier 42. The non-inverting input terminal 411 of the first amplifier 41 is electrically connected to the first output terminal 101, and the output terminal 412 is electrically connected to the input terminal of the first coil 20. The first amplifier 41 is used to amplify a first sine wave signal. The non-inverting input terminal 421 of the second amplifier 42 is electrically connected to the second output terminal 102, the inverting input terminal 423 is electrically connected to the inverting input terminal 413 of the first amplifier 41, and the output terminal 422 is electrically connected to the input terminal of the second coil 21. The second amplifier 42 is used to amplify a second sine wave signal.

[0051] Specifically, refer to Figure 2 The first amplifier 41 can be used to amplify a first sine wave signal, and the second amplifier 42 can be used to amplify a second sine wave signal. Therefore, the non-inverting input terminal 411 of the first amplifier 41 is electrically connected to the first output terminal 101, and the non-inverting input terminal 421 of the second amplifier 42 is electrically connected to the second output terminal 102. In another optional embodiment, a first matching circuit 43 is included between the non-inverting input terminal 411 of the first amplifier 41 and the first output terminal 101, and a second matching circuit 44 is included between the non-inverting input terminal 421 of the second amplifier 42 and the first output terminal 102, wherein R13, R12, C24, and C23 constitute a differentiating circuit. Further, referring to... Figure 2The inverting input terminal 413 of the first amplifier 41 and the inverting input terminal 423 of the second amplifier 42 are electrically connected, and the same feedback resistor is used to ensure that the amplification factor of the first amplifier 41 and the second amplifier 42 is the same, so that the first sine wave signal and the second sine wave signal remain a differential signal after passing through the first amplifier 41 and the second amplifier 42. Furthermore, the output terminal 412 of the first amplifier 41 is electrically connected to the input terminal of the first coil 20, and the output terminal 422 of the second amplifier 42 is electrically connected to the input terminal of the second coil 21, so that the two amplified sine wave signals are respectively input into the first coil 20 and the second coil 21, thereby enabling the measurement of the ferromagnetic content of the sample to be tested.

[0052] In another alternative embodiment, reference continues... Figure 2 The DDS amplifier circuit also includes a DC bias circuit 45 and a DC blocking circuit 46. The DC bias circuit 45 includes a first resistor 451 and a second resistor 452, which are connected in series with the first power supply terminal and the ground terminal, and are connected to form a second connection node 453. The second connection node 453 is electrically connected to the non-inverting input terminal 411 of the first amplifier 41 and the non-inverting input terminal 421 of the second amplifier 42. The DC blocking circuit 46 includes a first capacitor C28 and a second capacitor C29. The first capacitor C28 is connected in series between the output terminal 412 of the first amplifier 41 and the input terminal of the first coil 20. The second capacitor C29 is connected in series between the output terminal 422 of the second amplifier 42 and the input terminal of the second coil 21.

[0053] Specifically, since the first amplifier 41 and the second amplifier 42 are powered by the positive power rail, and the first and second sine wave signals generated by the DDS signal source 10 are periodic signals symmetrical about zero potential, with their amplitude fluctuating positively in the positive half-cycle and negatively in the negative half-cycle, a DC bias circuit 45 is added to the DDS amplifier circuit 40 to ensure that the first amplifier 41 and the second amplifier 42 can work normally. The DC bias circuit 45 includes a first resistor 451 and a second resistor 452, which are connected in series with the first power supply terminal and the ground terminal, and are connected to form a second connection node 453. The second connection node 453 is electrically connected to the non-inverting input terminal 411 of the first amplifier 41 and the non-inverting input terminal 421 of the second amplifier 42, thereby increasing the amplitude of the first sine wave signal input to the non-inverting input terminal 411 of the first amplifier 41 and the second sine wave signal input to the non-inverting input terminal 421 of the second amplifier 42, so that the amplitudes of the first sine wave signal and the second sine wave signal are both greater than 0.

[0054] Furthermore, a DC blocking circuit 46 is provided at the output terminals of the first amplifier 41 and the second amplifier 42. The DC blocking circuit 46 includes a first capacitor C28 and a second capacitor C29. The first capacitor C28 is connected in series between the output terminal 412 of the first amplifier 41 and the input terminal of the first coil 20. The second capacitor C29 is connected in series between the output terminal 422 of the second amplifier 42 and the input terminal of the second coil 21. Since the capacitor has the function of passing AC and blocking DC, the first and second sine wave signals, after being raised by the DC bias circuit 45, are restored to periodic signals symmetrical about zero potential after passing through the first capacitor C28 and the second capacitor C29. The amplified first and second sine wave signals are then input into the first coil 20 and the second coil 21, respectively.

[0055] Optionally, continue to refer to Figure 2 The measurement circuit also includes a differential signal amplifier circuit 50 and an analog-to-digital converter unit 60. The differential signal amplifier circuit 50 is electrically connected to the first connection node 22 and is used to amplify the differential change signal to generate an amplified change signal. The analog-to-digital converter unit 60 is electrically connected to the output terminal of the differential signal amplifier circuit 50 and is used to perform analog-to-digital conversion on the amplified change signal to generate a digital change signal. The processor is used to determine the ferromagnetic content of the sample to be tested based on the digital change signal.

[0056] Specifically, the first and second sinusoidal signals, amplified by the DDS amplifier circuit 40, are input to the first coil 20 and the second coil 21, respectively, and output from the first connection node 22 at the output terminals of the first coil 20 and the second coil 21, thus obtaining a differential signal. (Reference) Figure 2 The first connection node 22 is connected to the differential signal amplifier circuit 50 to amplify the differential change signal and generate an amplified change signal. Furthermore, the analog-to-digital conversion unit 60 is electrically connected to the output of the differential signal amplifier circuit 50 to perform analog-to-digital conversion on the amplified change signal, generating a digital change signal. This digital change signal is then input into the processor, which can determine the ferromagnetic content of the sample based on the digital change signal.

[0057] Optionally, continue to refer to Figure 2 The measurement circuit also includes a digital positioner 70; the digital positioner 70 includes two input terminals and one output terminal; the two input terminals of the digital positioner 70 receive a first sine wave signal and a second sine wave signal respectively, and the output terminal is electrically connected to the differential signal amplifier circuit 50; the digital positioner 70 is used to adjust its own impedance to output a reference differential change signal; wherein, the reference differential change signal is the same as the differential change signal formed by the first connection node 22 when no sample to be tested is placed in either the first coil 20 or the second coil 21.

[0058] Specifically, the digital locator 70 includes two input terminals, a fifth input terminal 701 and a sixth input terminal 702. The fifth input terminal 701 is used to receive a first sine wave signal, and the sixth input terminal 702 is used to receive a second sine wave signal. The first and second sine wave signals are coupled and output at the output terminal 703 of the digital locator 70. Theoretically, the signal output from the output terminal 703 of the digital locator 70 is the same as the signal at the first connection node 22, both being signals with an amplitude of 0. However, in practical applications, due to the difference between the first coil 20 and the second coil 21, the first sine wave signal after passing through the first coil 20 and the second sine wave signal after passing through the second coil 21 may no longer be standard differential signals, causing the amplitude of the differential change signal at the first connection node 22 to be non-zero.

[0059] Based on this, the impedance of the digital positioner 70 can be adjusted to output a reference differential change signal at its output terminal 703. This reference differential change signal is the same as the differential change signal formed when no sample is placed in either the first coil 20 or the second coil 21 at the first connection node 22. For example, the digital positioner 70 can be an 8-bit 256-level digital positioner with a 5K resistance value. By controlling the digital positioner 70 with a microcontroller to write different binary data, the resistance values ​​of the fifth input terminal 701 and the output terminal 703, as well as the resistance values ​​of the sixth input terminal 702 and the output terminal 703, can be changed, thereby ensuring that the reference differential change signal and the differential change signal are identical.

[0060] Optionally, continue to refer to Figure 2 The differential signal amplifier circuit 50 includes a third amplifier 51 and a fourth amplifier 52; the non-inverting input terminal 511 of the third amplifier 51 is electrically connected to the first connection node 22, the non-inverting input terminal 521 of the fourth amplifier 52 is electrically connected to the output terminal of the digital positioner 70, and the inverting input terminal 512 of the third amplifier 51 and the inverting input terminal 522 of the fourth amplifier 52 are electrically connected; the third amplifier 51 is used to amplify the differential change signal of the first connection node 22, and the fourth amplifier 52 is used to amplify the reference differential change signal.

[0061] Specifically, the differential signal amplifier circuit 50 includes a third amplifier 51 and a fourth amplifier 52. The differential change signal and the reference differential change signal are input to the third amplifier 51 and the fourth amplifier 52 respectively to achieve equal amplification. Further, the non-inverting input terminal 511 of the third amplifier 51 is electrically connected to the first connection node 22 to receive the differential change signal. In addition, the first sine wave signal and the second sine wave signal, through resistors R22 and R23, act together with the reference differential change signal at the output terminal of the digital positioner 70 at the non-inverting input terminal 521 of the fourth amplifier 52. The inverting input terminals 512 of the third amplifier 51 and 522 of the fourth amplifier 52 are electrically connected. Simultaneously, the third amplifier 51 and the fourth amplifier 52 use the same feedback resistor. Therefore, when the reference differential change signal and the differential change signal are the same, the signals obtained at the output terminals of the third amplifier 51 and the fourth amplifier 52 are also the same.

[0062] Similarly, since the differential change signal at the first connection node 22 and the reference differential change signal output from the output terminal 703 of the digital positioner 70 may both exhibit negative amplitude fluctuations, a second DC bias circuit 53 is added to ensure the normal operation of the differential signal amplifier circuit 50. The second DC bias circuit 53 includes a third resistor 531 and a fourth resistor 532, which are connected in series with the second power supply terminal and the ground terminal, and are connected to form a third connection node 533. The third connection node 533 is electrically connected to the non-inverting input terminal 511 of the third amplifier 51 and the non-inverting input terminal 521 of the fourth amplifier 52, thereby ensuring that the amplitudes of the differential change signal and the reference differential change signal are always positively biased.

[0063] Furthermore, amplification matching circuitry is also included around the third amplifier 51 and the fourth amplifier 52, such as... Figure 2 As shown, C37, C38, R26, R27, R29 and R28 form an amplification and matching circuit, and C40, C41C and C42 form a filter circuit.

[0064] Optionally, continue to refer to Figure 2 The analog-to-digital conversion unit 60 is a comparator. The output terminals of the third amplifier 51 and the fourth amplifier 52 are electrically connected to the two input terminals of the comparator, respectively. The comparator is used to compare the differential change signal of the first connection node 22 with the reference differential change signal to generate a digital change signal.

[0065] Specifically, the signals obtained from the output terminals of the third amplifier 51 and the fourth amplifier 52 are respectively input to the two input terminals of the analog-to-digital converter 60. The analog-to-digital converter 60 is a comparator. Therefore, the signals obtained from the output terminals of the third amplifier 51 and the fourth amplifier 52 are compared in the comparator. That is, the differential change signal of the first connection node 22 is compared with the reference differential change signal output by the digital positioner 70. A digital change signal is generated based on the comparison result.

[0066] Furthermore, during the process of adjusting the resistance value between the input and output terminals of the digital locator 70 to make the reference differential change signal and the differential change signal the same, the voltage difference between the reference differential change signal and the differential change signal can be read based on the digital change signal output by the analog-to-digital converter 60, thereby determining the final value determined by the digital locator 70. For example, the digital locator 70 can be a 5K resistor value 8-bit 256-level digital locator. After the system is powered on, the digital locator 70 can be programmed with values ​​from 0 to 255 sequentially via a microcontroller. For each value written, the voltage difference between the reference differential change signal and the differential change signal is read by the analog-to-digital converter 60. The value with the smallest voltage difference during the entire sequential writing process is determined as the final value determined by the digital locator 70, and the signal output by the digital locator 70 at this point is used as the reference differential change signal.

[0067] Furthermore, after obtaining the reference differential change signal, when the sample to be tested is inserted into the first coil 20 or the second coil 21, the magnetic field of the coil inserted into the sample will change due to the presence of ferromagnetic material in the sample. This will cause a change in the impedance of the coil, making the differential change signal at the first connection node 22 no longer the same as the reference differential change signal. Consequently, the digital change signal after passing through the analog-to-digital conversion unit 60 will change. Thus, the processor can determine the content of ferromagnetic material in the sample by detecting the digital change signal.

[0068] The embodiments of the present invention effectively compensate for the measurement error caused by the inconsistency between the first coil and the second coil by using a digital positioner, thereby improving the measurement accuracy of the ferromagnetic content in the sample to be tested.

[0069] Optionally, Figure 3 This is a schematic diagram of a printed circuit board with an induction coil wound according to an embodiment of the present invention, as shown below. Figure 3 As shown, the first coil 20 and the second coil 21 are disposed in at least one conductive line layer of the printed circuit board.

[0070] Specifically, the first coil 20 and the second coil 21 are disposed in at least one conductive line layer of the printed circuit board. Since the printed circuit board processing technology has higher processing precision, the first coil 20 and the second coil 21 have better consistency compared with the traditional method of winding with a skeleton and enameled wire. Furthermore, the fabrication of coils on the printed circuit board can realize automated production and processing, thereby improving product yield.

[0071] Further, in an optional embodiment, the printed circuit board can be configured with 8-10 layers. The number of turns of the first coil 20 and the second coil 21 on each layer ranges from 8 to 10, the line spacing ranges from 0.15 to 0.2 mm, the line width ranges from 0.2 to 0.3 mm, and the spacing between coils ranges from 15 to 20 mm. For example, the signal line can be routed clockwise for 8 turns along the top layer of the printed circuit board, where the line width can be 0.2 mm and the line spacing can be 0.15 mm. Then, it is routed through a hole into the second layer of the printed circuit board for another 8 turns, until the last layer of the printed circuit board is reached. If the printed circuit board has 8 layers, after routing, the first or second coil has a total of 64 turns, with an internal resistance of approximately 2 ohms and an inductance of approximately 1 mH.

[0072] Optionally, continue to refer to Figure 3 The printed circuit board includes a metal layer cutout area 80, where the first coil 20 and the second coil 21 are both located. In addition, no conductive structures other than the first coil 20 and the second coil 21 are provided in each conductive line layer of the metal layer cutout area 80.

[0073] Specifically, to reduce the shielding effect of other copper foils or conductive structures on the magnetic field in the printed circuit board, a metal layer cutout area 80 can be provided in a certain area around the first coil 20 and the second coil 21. Furthermore, no conductive structures other than the first coil 20 and the second coil 21 are provided in the conductive lines of the metal layer cutout area 80, thereby enhancing the magnetic field induction sensitivity. The size of the metal layer cutout area ranges from 60×90mm to 100×100mm. For example, a cutout area larger than 60mm×60mm can be provided around the first coil 20 and the second coil 21 on the printed circuit board.

[0074] In this embodiment of the invention, by fabricating the first coil and the second coil on a printed circuit board, the first coil and the second coil have higher consistency, thereby improving the measurement accuracy of the ferromagnetic content in the sample to be tested.

[0075] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A ferromagnetic content measurement circuit based on DDS technology, characterized in that, include: The DDS signal source includes a first output terminal and a second output terminal. The first output terminal is used to output a first sine wave signal, and the second output terminal is used to output a second sine wave signal. The first sine wave signal and the second sine wave signal constitute a set of differential signals. A first coil and a second coil are arranged in the same plane; the input terminal of the first coil receives the first sine wave signal, and the input terminal of the second coil receives the second sine wave signal; the output terminals of the first coil and the second coil are electrically connected to form a first connection node; the first coil or the second coil is used to place the sample to be tested so that the first connection node forms a differential change signal; A processor is used to determine the ferromagnetic content of the sample to be tested based on the differential change signal.

2. The measurement circuit according to claim 1, characterized in that, The measurement circuit also includes a DDS amplifier circuit; The input terminal of the DDS amplifier circuit is electrically connected to the first output terminal and the second output terminal, respectively, and the output terminal is electrically connected to the input terminal of the first coil and the input terminal of the second coil, respectively. The DDS amplifier circuit is used to amplify the first sine wave signal and the second sine wave signal, respectively.

3. The measurement circuit according to claim 2, characterized in that, The DDS amplifier circuit includes a first amplifier and a second amplifier. The non-inverting input terminal of the first amplifier is electrically connected to the first output terminal, and the output terminal is electrically connected to the input terminal of the first coil; the first amplifier is used to amplify the first sine wave signal. The non-inverting input terminal of the second amplifier is electrically connected to the second output terminal, the inverting input terminal is electrically connected to the inverting input terminal of the first amplifier, and the output terminal is electrically connected to the input terminal of the second coil; the second amplifier is used to amplify the second sine wave signal.

4. The measurement circuit according to claim 3, characterized in that, The DDS amplifier circuit also includes a DC bias circuit and a DC blocking circuit; The DC bias circuit includes a first resistor and a second resistor, which are connected in series with a first power supply terminal and a ground terminal, and the first resistor and the second resistor are connected to form a second connection node; the second connection node is electrically connected to the non-inverting input terminal of the first amplifier and the non-inverting input terminal of the second amplifier, respectively. The DC blocking circuit includes a first capacitor and a second capacitor; the first capacitor is connected in series between the output terminal of the first amplifier and the input terminal of the first coil; the second capacitor is connected in series between the output terminal of the second amplifier and the input terminal of the second coil.

5. The measurement circuit according to claim 1, characterized in that, The measurement circuit also includes a differential signal amplifier circuit and an analog-to-digital converter unit; The differential signal amplification circuit is electrically connected to the first connection node and is used to amplify the differential change signal to generate an amplified change signal. The analog-to-digital conversion unit is electrically connected to the output terminal of the differential signal amplifier circuit, and is used to perform analog-to-digital conversion on the amplified changing signal to generate a digital changing signal; The processor is used to determine the ferromagnetic content of the sample to be tested based on the digital change signal.

6. The measurement circuit according to claim 5, characterized in that, The measurement circuit also includes a digital locator; the digital locator includes two input terminals and one output terminal. The digital locator receives the first sine wave signal and the second sine wave signal at its two input terminals, respectively, and its output terminal is electrically connected to the differential signal amplifier circuit. The digital positioner is used to adjust its own impedance to output a reference differential change signal; wherein the reference differential change signal is the same as the differential change signal formed when the first connection node has no sample to be tested in either the first coil or the second coil.

7. The measurement circuit according to claim 6, characterized in that, The differential signal amplifier circuit includes a third amplifier and a fourth amplifier; The non-inverting input terminal of the third amplifier is electrically connected to the first connection node, the non-inverting input terminal of the fourth amplifier is electrically connected to the output terminal of the digital positioner, and the inverting input terminal of the third amplifier is electrically connected to the inverting input terminal of the fourth amplifier. The third amplifier is used to amplify the differential change signal of the first connection node, and the fourth amplifier is used to amplify the reference differential change signal.

8. The measurement circuit according to claim 7, characterized in that, The analog-to-digital conversion unit is a comparator, and the output terminals of the third amplifier and the fourth amplifier are respectively electrically connected to the two input terminals of the comparator. The comparator is used to compare the differential change signal of the first connection node with the reference differential change signal to generate the digital change signal.

9. The measurement circuit according to claim 1, characterized in that, The first coil and the second coil are disposed in at least one conductive line layer of the printed circuit board.

10. The measurement circuit according to claim 9, characterized in that, The printed circuit board includes a metal layer cutout area, where both the first coil and the second coil are located. Furthermore, no conductive structures other than the first coil and the second coil are provided in each conductive line layer of the metal layer cutout area.

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