A current sensor and current measurement method based on nuclear magnetic resonance

Abstract

The present invention provides a current sensor and current measurement method based on nuclear magnetic resonance, comprising a conversion unit, a measurement unit, and a calculation unit; the conversion unit comprises a current conversion coil that converts the current to be measured into a magnetic field, and a nuclear magnetic resonance sample that converts the magnetic field into a frequency; the measurement unit comprises a sweep frequency controller, a radio frequency power amplifier, a radio frequency transmitting coil, a radio frequency receiving coil, a low-noise amplifier, and a waveform shaper, which are sequentially connected via signals; the calculation unit comprises a clock reference source, a frequency calculation circuit, and a current calculation circuit, which are sequentially connected via signals, and the frequency calculation circuit is also respectively connected to the output signals of the sweep frequency controller and the waveform shaper; the workflow mainly includes three basic steps: sweep frequency, frequency locking, and measurement. The current sensor and current measurement method disclosed in the present invention do not rely on any voltage reference source, and achieve high-stability current measurement through a high-precision clock source.

Description

Technical Field

[0001] The present invention relates to the technical field of basic electrical quantity measurement, and in particular to a current sensor and a current measurement method based on nuclear magnetic resonance. Background Art

[0002] High-stability current sensors are precision electronic sensing devices used to measure and monitor current intensity. Based on their measurement principles, they can be categorized into shunts, electromagnetic current transformers, and electronic current transformers. As detection devices, current sensors' inherent stability and accuracy are key evaluation criteria.

[0003] While traditional current sensors play an important role in many applications, they inevitably have limitations. These limitations include, but are not limited to, component aging and performance degradation over time. In actual use, the components of traditional current sensors are often affected by environmental factors such as temperature and humidity, leading to errors such as temperature drift and zero drift. Long-term operation causes component aging, resulting in reduced accuracy. Traditional current sensors often require a high-precision voltage reference as a measurement basis. Therefore, the measurement accuracy and stability of traditional current sensors are also limited by the accuracy and stability of the voltage reference used. As the circuit operates over time and the environment changes, these error factors will gradually accumulate, further weakening the performance of the sensor. Current voltage reference stability indicators are at the ppm level, which restricts the design of high-performance measuring instruments and precision high-power voltage and current sources. Summary of the Invention

[0004] The object of the present invention is to provide a current sensor and a current measurement method based on nuclear magnetic resonance to solve the above-mentioned deficiencies in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A current sensor based on nuclear magnetic resonance includes a conversion unit, a measuring unit, and a calculation unit; the conversion unit includes a current conversion coil that converts the current to be measured into a magnetic field, and a nuclear magnetic resonance sample that converts the magnetic field into a frequency; the measuring unit includes a sweep frequency controller, a radio frequency power amplifier, a radio frequency transmitting coil, a radio frequency receiving coil, a low-noise amplifier, and a waveform shaper that are sequentially connected via signals; the calculation unit includes a clock reference source, a frequency calculation circuit, and a current calculation circuit that are sequentially connected via signals, and the frequency calculation circuit is also respectively connected to the output signals of the sweep frequency controller and the waveform shaper.

[0007] Furthermore, the current conversion coil adopts a Helmholtz coil, a solenoid coil or other coil structures capable of generating a uniform magnetic field, and the nuclear magnetic resonance sample is placed in the center of the uniform magnetic field.

[0008] Furthermore, the radio frequency transmitting coil and the radio frequency receiving coil are arranged around the nuclear magnetic resonance sample, and the axial direction of the radio frequency transmitting coil and the axial direction of the radio frequency receiving coil are perpendicular to each other and are both perpendicular to the axial direction of the current conversion coil.

[0009] A current measurement method based on nuclear magnetic resonance is implemented based on the above-mentioned current sensor and specifically includes the following steps:

[0010] S1. Connect the current to be measured to the current conversion coil to generate a magnetic field, and output a sine wave signal of a specific frequency through the sweep frequency controller;

[0011] S2. The sine wave signal excites the radio frequency transmitting coil through the radio frequency power amplifier to generate an excitation magnetic field, and searches for the magnetic resonance signal of the nuclear magnetic resonance sample;

[0012] S3, collecting the magnetic resonance signal of the nuclear magnetic resonance sample through the radio frequency receiving coil, and inputting it into the frequency calculation circuit after processing by the low noise amplifier and the waveform shaper to collect the radio frequency receiving coil signal;

[0013] S4, setting the sweep frequency interval of the sweep frequency controller and increasing it step by step, repeating S1 to S4 until a valid nuclear magnetic resonance signal is found and the magnetic resonance frequency of the nuclear magnetic resonance sample is calculated;

[0014] S5, calculating the frequency difference based on the magnetic resonance frequency of the NMR sample obtained in step S4;

[0015] This step can be expressed by the following formulas (1) and (2):

[0016] (1)

[0017] (2)

[0018] In formula (1) and (2): represents the frequency of the exciting magnetic field; Indicates the frequency sweep interval; Indicates the level of increase in sweep frequency interval; Indicates based on the sweep interval The excitation magnetic field frequency; Indicates the output frequency of the sweep frequency controller; represents the magnetic resonance frequency of the nuclear magnetic resonance sample calculated in step S4; Indicates frequency difference;

[0019] S6. Adjust the output frequency of the sweep frequency controller based on the frequency difference, and repeat the above steps until the frequency difference is zero;

[0020] This step can be expressed by the following formulas (3) and (4):

[0021] (3)

[0022] (4)

[0023] In formula (3) and (4): ; Indicates the The output frequency of the swept frequency controller after the adjustment; Indicates the The frequency difference is calculated after adjusting the output frequency of the sweep frequency controller; Indicates the The magnetic resonance frequency of the NMR sample is calculated after adjusting the output frequency of the sweep controller;

[0024] S7. Based on the magnetic resonance frequency of the nuclear magnetic resonance sample when the frequency difference is zero, the locked resonance frequency of the nuclear magnetic resonance sample is calculated by a phase contrast method and with a clock reference source as a high-precision reference;

[0025] S8. Calculating the current value based on the linear relationship between the locked resonant frequency and the current to be measured;

[0026] This step can be expressed by the following formula (5):

[0027] (5)

[0028] In formula (5): Indicates the current to be measured; represents the locked magnetic resonance frequency of the NMR sample; Represents a constant related to the properties of the current conversion coil.

[0029] It can be seen from the above technical solutions that the current sensor and current measurement method disclosed in the present invention do not rely on any voltage reference source, and achieve high-stability current measurement through a high-precision clock source. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the structure of the current sensor of the present invention;

[0031] Figure 2 Schematic diagram of the steps of the current measurement method of the present invention;

[0032] In the figure: 1. Current conversion coil; 2. Nuclear magnetic resonance sample; 3. Sweep frequency controller; 4. RF power amplifier; 5. RF transmitting coil; 6. RF receiving coil; 7. Low noise amplifier; 8. Waveform shaper; 9. Clock reference source; 10. Frequency calculation circuit; 11. Current calculation circuit. DETAILED DESCRIPTION

[0033] A preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings.

[0034] like Figure 1 The nuclear magnetic resonance-based current sensor shown includes a conversion unit, a measuring unit, and a computing unit; the conversion unit includes a current conversion coil 1 that converts the current to be measured into a magnetic field, and a nuclear magnetic resonance sample 2 that converts the magnetic field into a frequency; the measuring unit includes a sweep frequency controller 3, a radio frequency power amplifier 4, a radio frequency transmitting coil 5, a radio frequency receiving coil 6, a low noise amplifier 7, and a waveform shaper 8 that are sequentially connected through signals; the computing unit includes a clock reference source 9, a frequency calculation circuit 10, and a current calculation circuit 11 that are sequentially connected through signals, and the frequency calculation circuit 10 is also signal-connected to the output ends of the sweep frequency controller 3 and the waveform shaper 8, respectively.

[0035] In specific use, the current conversion coil 1 adopts a Helmholtz coil, a solenoid coil or other coil structure capable of generating a uniform magnetic field, and the nuclear magnetic resonance sample is placed in the center of the uniform magnetic field. Figure 1 As shown, the current conversion coil described in this preferred embodiment is a Helmholtz coil structure, consisting of two coils with exactly the same radius and number of turns. These coils are coaxially arranged, and their spacing is equal to the radius of the coil; this structure can generate an approximately uniform magnetic field inside it, that is, the magnetic field uniformity is relatively high. The RF transmitting coil 4 and the RF receiving coil 5 are arranged around the nuclear magnetic resonance sample 2, and the axial direction of the RF transmitting coil 4 and the axial direction of the RF receiving coil 5 are perpendicular to each other and both perpendicular to the axial direction of the current conversion coil 2; specifically, the RF transmitting coil 5 adopts a solenoid coil and is placed in front of the nuclear magnetic resonance sample. It can generate an RF excitation magnetic field and excite nuclear spin resonance in the nuclear magnetic resonance sample 2 to achieve phase synchronization of nuclear spin precession; the sinusoidal wave signal generated by the sweep controller 3 is based on the signal frequency of the clock reference source 9, so that it can generate a stable sinusoidal wave signal.

[0036] like Figure 2 The current measurement method based on nuclear magnetic resonance is implemented based on the above-mentioned current sensor and specifically includes the following steps:

[0037] S1. Connect the current to be measured to the current conversion coil to generate a magnetic field, and output a sine wave signal of a specific frequency through the sweep frequency controller.

[0038] S2. The sine wave signal excites the RF transmitting coil through the RF power amplifier to generate an excitation magnetic field, and searches for the magnetic resonance signal of the nuclear magnetic resonance sample.

[0039] Steps S1 and S2 are the frequency sweep process of the current sensor.

[0040] S3. The magnetic resonance signal of the nuclear magnetic resonance sample is collected through the radio frequency receiving coil, and after being processed by the low noise amplifier and the waveform shaper, it is input into the frequency calculation circuit to collect the radio frequency receiving coil signal.

[0041] S4. Set the sweep frequency interval of the sweep frequency controller and increase it step by step. Repeat S1 to S4 until a valid nuclear magnetic resonance signal is found and the magnetic resonance frequency of the nuclear magnetic resonance sample is calculated.

[0042] S5, calculating the frequency difference based on the magnetic resonance frequency of the NMR sample obtained in step S4;

[0043] This step can be expressed by the following formulas (1) and (2):

[0044] (1)

[0045] (2)

[0046] In formula (1) and (2): represents the frequency of the exciting magnetic field; Indicates the frequency sweep interval; Indicates the level of increase in sweep frequency interval; Indicates based on the sweep interval The excitation magnetic field frequency; Indicates the output frequency of the sweep frequency controller; represents the magnetic resonance frequency of the nuclear magnetic resonance sample calculated in step S4; Indicates frequency difference.

[0047] S6. Adjust the output frequency of the sweep frequency controller based on the frequency difference, and repeat the above steps until the frequency difference is zero;

[0048] This step can be expressed by the following formulas (3) and (4):

[0049] (3)

[0050] (4)

[0051] In formula (3) and (4): ; Indicates the The output frequency of the swept frequency controller after the adjustment; Indicates the The frequency difference is calculated after adjusting the output frequency of the sweep frequency controller; Indicates the The magnetic resonance frequency of the nuclear magnetic resonance sample is calculated after adjusting the output frequency of the sweep frequency controller.

[0052] In specific operations, the frequency difference The size of is related to the coil resolution of the RF transmitting coil and the RF receiving coil. When the value is smaller than the resolution of the above two components, the frequency difference can be considered to be zero.

[0053] S7. Based on the magnetic resonance frequency of the nuclear magnetic resonance sample when the frequency difference is zero, the locked resonance frequency of the nuclear magnetic resonance sample is calculated by a phase contrast method and under the premise that a clock reference source is used as a high-precision reference.

[0054] The above-described embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A current measurement method based on nuclear magnetic resonance, which is implemented based on a current sensor, wherein the current sensor includes a conversion unit, a measurement unit, and a calculation unit; the conversion unit includes a current conversion coil that converts the current to be measured into a magnetic field, and a nuclear magnetic resonance sample that converts the magnetic field into a frequency; the measurement unit includes a sweep frequency controller, a radio frequency power amplifier, a radio frequency transmitting coil, a radio frequency receiving coil, a low noise amplifier, and a waveform shaper that are sequentially connected through signals; the calculation unit includes a clock reference source, a frequency calculation circuit, and a current calculation circuit that are sequentially connected through signals, and the frequency calculation circuit is also signal-connected to the output terminals of the sweep frequency controller and the waveform shaper respectively; characterized in that The current measurement method specifically comprises the following steps: S1. Connect the current to be measured to the current conversion coil to generate a magnetic field, and output a sine wave signal of a specific frequency through the sweep frequency controller; S2. The sine wave signal excites the radio frequency transmitting coil through the radio frequency power amplifier to generate an excitation magnetic field, and searches for the magnetic resonance signal of the nuclear magnetic resonance sample; S3, collecting the magnetic resonance signal of the nuclear magnetic resonance sample through the radio frequency receiving coil, and inputting it into the frequency calculation circuit after processing by the low noise amplifier and the waveform shaper to collect the radio frequency receiving coil signal; S4, setting the sweep frequency interval of the sweep frequency controller and increasing it step by step, repeating S1 to S3 until a valid nuclear magnetic resonance signal is found and the magnetic resonance frequency of the nuclear magnetic resonance sample is calculated; S5, calculating the frequency difference based on the magnetic resonance frequency of the NMR sample obtained in step S4; This step can be expressed by the following formulas (1) and (2): W1=W A +nΔW (1) ΔW1=W 01 -IN 00 (2) In formula (1) and (2): W A represents the frequency of the exciting magnetic field; ΔW represents the frequency sweep interval; n represents the number of levels of increase in the frequency sweep interval; W1 represents the frequency of the exciting magnetic field based on the frequency sweep interval ΔW; W 00 Indicates the output frequency of the sweep frequency controller; W 01 represents the magnetic resonance frequency of the NMR sample calculated in step S4; ΔW1 represents the frequency difference; S6. Adjust the output frequency of the sweep frequency controller based on the frequency difference, and repeat the above steps until the frequency difference is zero; This step can be expressed by the following formulas (3) and (4): IN i =In i-1 -ΔW i-1 (3) ΔW i =In 0i -IN 0i-1 (4) In formula (3) and (4): i ≥ 2; W i Represents the output frequency of the sweep frequency controller after the i-th adjustment; ΔW i represents the frequency difference calculated after adjusting the output frequency of the sweep frequency controller for the i-th time; W 0i represents the magnetic resonance frequency of the NMR sample calculated after adjusting the output frequency of the sweep controller for the i-th time; S7. Based on the magnetic resonance frequency of the nuclear magnetic resonance sample when the frequency difference is zero, the locked resonance frequency of the nuclear magnetic resonance sample is calculated by a phase contrast method and with a clock reference source as a high-precision reference; S8. Calculating the current value based on the linear relationship between the locked resonant frequency and the current to be measured; This step can be expressed by the following formula (5): I = KW 0lock (5) In formula (5): I represents the current to be measured; W 0lock represents the locked magnetic resonance frequency of the NMR sample; K represents a constant related to the properties of the current conversion coil.

2. The current measurement method based on nuclear magnetic resonance according to claim 1, characterized in that: The current conversion coil adopts a Helmholtz coil, a solenoid coil or other coil structures capable of generating a uniform magnetic field, and the nuclear magnetic resonance sample is placed in the center of the uniform magnetic field.

3. The current measurement method based on nuclear magnetic resonance according to claim 2, characterized in that: The radio frequency transmitting coil and the radio frequency receiving coil are arranged around the nuclear magnetic resonance sample. The axial directions of the radio frequency transmitting coil and the axial directions of the radio frequency receiving coil are perpendicular to each other and are both perpendicular to the axial direction of the current conversion coil.

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