Alternating-current voltage measuring method for lead error correction

Abstract

The invention discloses an alternating-current voltage measurement method for lead error correction. The method comprises the following steps of: analyzing and acquiring a voltage correction value brought by a lead error by adopting finite element simulation software; based on a target voltage, adding the target voltage with the voltage correction amount to obtain a first voltage, and modulating a first voltage waveform expected to be synthesized into a series of digital code patterns by using delta-sigma modulation; storing the digital code pattern in a pulse code pattern generator, and converting the digital code pattern into a corresponding high-speed pulse; driving a Josephson junction of the quantum voltage system by using a high-speed pulse to generate a quantum voltage pulse sequence containing waveform information of a first voltage expected to be synthesized; the quantum voltage system outputs a first voltage signal through the Josephson junction end, namely a voltage waveform expected to be synthesized; the first voltage is transmitted to a tested instrument through a lead, and the obtained voltage is the target voltage. The lead error is calculated through the finite element analysis method, and the influence of the lead error is reduced.

Description

Technical Field

[0001] This invention relates to the field of quantized low-frequency voltage technology, and in particular to an AC voltage measurement method with lead error correction. Background Technology

[0002] Based on the principle of magnetic flux quantum, the pulse-driven quantum voltage system uses a series of high-speed current pulses to drive a Josephson array. The Josephson array, once driven, generates magnetic flux quanta with a time integral area equal to h / (2e). Through filtering, an AC voltage waveform can be synthesized. The process of synthesizing a standard voltage waveform using the pulse-driven Josephson voltage system consists of three steps: modulating the desired waveform into a series of digital codes using Δ-Σ modulation; storing the digital codes in a pulse code generator and converting them into corresponding high-speed pulses; and driving the Josephson array with these high-speed pulses to generate a quantum voltage pulse sequence containing information about the waveform to be synthesized. These quantum voltage pulses are reproductions of the Δ-Σ modulated digital codes, and low-pass filtering removes the quantization noise. The voltage signal obtained after filtering is the desired synthesized voltage waveform. Because the quantum voltage generated from the Josephson array needs to pass through the output link of the pulse-driven quantum voltage system to be transmitted to the instrument under test (usually a calibrated AC voltmeter), the voltage value transmitted to the instrument under test is not exactly equal to the quantum voltage value generated by the Josephson array. The main causes of error are the resonance in the circuit caused by the inductance and capacitance on the quantum voltage output leads, and the thermoelectric potential caused by the temperature change from the liquid helium temperature range to room temperature. Since the quantum voltage is generated at low temperatures while the measuring instrument is at room temperature, the influence of the long voltage leads connected to the load and potentially high-frequency circuits becomes the main component of the uncertainty, with a maximum influence of three to four orders of magnitude. When the synthesized quantum voltage frequency reaches MHz, the main source of error is voltage lead error. Currently, lead error is mainly reduced by minimizing the length of the internal leads of the cryogenic test probe, reducing the length of the test leads at room temperature, and improving cable processing technology when designing pulse-driven quantum voltage systems. However, due to the requirements of overall system operation, the lead length cannot be made very small, so the above methods cannot effectively reduce the influence of lead error.

[0003] There is an urgent need to propose a method for correcting lead wire errors and a method for measuring AC voltage, so as to reduce the impact of lead wire errors on the measurement. Summary of the Invention

[0004] The purpose of this invention is to provide an AC voltage measurement method with lead error correction to solve the problem of reduced signal accuracy of pulse-driven quantum voltage system output due to lead error. The method uses finite element analysis technology and finite element simulation software to theoretically calculate the lead error of the pulse-driven quantum voltage system, and corrects the error during the operation of the pulse-driven quantum voltage system, thereby reducing the impact of lead error on measurement and improving the accuracy of AC voltage measurement.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an AC voltage measurement method with lead error correction, comprising the following steps:

[0007] The target voltage was obtained by analyzing the data using finite element simulation software.

[0008] The first voltage (i.e., the excitation voltage at the input of the Josephson junction) is adjusted according to the target voltage, and the desired synthesized first voltage waveform is modulated into a series of digital codes using Δ-Σ modulation.

[0009] The digital code pattern is stored in the pulse code generator and converted into a corresponding high-speed pulse;

[0010] By using high-speed pulses to drive the Josephson junction of a quantum voltage system, a quantum voltage pulse sequence containing waveform information of the desired first voltage is generated.

[0011] The quantum voltage system outputs a first voltage signal through the Josephson junction, which is the voltage waveform to be synthesized.

[0012] The first voltage is transmitted to the instrument under test through the lead wire, and the obtained voltage is the target voltage.

[0013] In some possible implementations, before the quantum voltage system outputs the first voltage signal through the Josephson junction, it further includes filtering out quantization noise carried by the waveform of the desired synthesized first voltage by low-pass filtering.

[0014] In some possible implementations, the step of using finite element simulation software to analyze and obtain the target voltage specifically includes:

[0015] The connection between the quantum voltage system and the leads is simplified and modeled, while the leads are modeled based on actual lead parameters.

[0016] Set the lead material properties, including temperature-related electrical / thermal / thermoelectric parameters, and assign temperature-dependent physical properties to each layer of material;

[0017] Multiphysics coupling configuration, finite element simulation software analyzes and solves electromagnetic field, heat transfer, thermoelectric effect simultaneously, coupled electromagnetic field and temperature field, and performs bidirectional coupled iterative solution;

[0018] Mesh generation strikes a balance between accuracy and efficiency;

[0019] This includes setting the boundary conditions for the first voltage;

[0020] The target voltage is obtained by coupling solution;

[0021] If the target voltage is not the same as the value of the AC voltmeter being calibrated, the boundary conditions of the first voltage are reset until the target voltage is the same as the value of the AC voltmeter being calibrated.

[0022] In some possible implementations, the connection between the quantum voltage system and the leads is simplified and modeled according to actual lead parameters, specifically including:

[0023] The lead input terminal is connected to the Josephson junction of the quantum voltage system. The Josephson junction is simplified to a series connection of an ideal AC voltage source and the Josephson junction matching impedance. The lead output terminal is connected to the instrument under test. The instrument under test can be simplified to a parallel connection of an ideal AC voltmeter and the input impedance of the instrument under test.

[0024] The lead wire is a coaxial cable, consisting of three layers: a central conductor layer, an insulation material layer, and a shielding layer. A geometric model is established based on the actual parameters of each part of the cable.

[0025] In some possible implementations, the setting of lead material properties, including temperature-related electrical / thermal / thermoelectric parameters, and the assignment of temperature-dependent physical properties to each layer of material, specifically includes:

[0026] Central conductor layer: electrical conductivity, which decreases with increasing temperature, and at 4K the conductivity is significantly higher than that at room temperature due to the quantum confinement effect; thermal conductivity, specific heat capacity, density, Seebeck coefficient; Josephson junction operates in the 4K temperature range.

[0027] Insulating material layer: relative permittivity, volume conductivity, thermal conductivity, specific heat capacity, Seebeck coefficient;

[0028] Shielding layer: conductivity, specific heat capacity, Seebeck coefficient.

[0029] In some possible implementations, the multiphysics coupling configuration, finite element simulation software simultaneously analyzes and solves for electromagnetic fields, heat transfer, and thermoelectric effects, coupling the electromagnetic field and temperature field for bidirectional coupled iterative solutions, specifically including:

[0030] Electromagnetic field analysis, based on Maxwell's equations, in frequency domain form, input port ( Figure 2Left Port 1) is set to 50Ω AC voltage source excitation; output port ( Figure 2 Port2 on the right is set as a high-impedance load to simulate the input impedance of the instrument under test. The electric field distribution and current density distribution of the coaxial cable are solved to obtain the conductor loss and dielectric loss.

[0031] Temperature field analysis was performed based on the Fourier heat conduction equation. The input temperature was set to 4K and the output temperature was set to 20℃. Joule heating was used as the heat source to solve for the temperature distribution of the coaxial cable.

[0032] Electric field analysis, based on Seebeck's equations, solves for the Seebeck thermoelectric potential. The thermoelectric potential generated by the Seebeck effect is superimposed on the electromagnetic field voltage as an additional potential.

[0033] Feedback iteration: Temperature changes affect the conductivity of the central conductor layer of the coaxial cable and the dielectric constant of the insulating material. The parameters are iterated through bidirectional coupling until convergence.

[0034] In some possible implementations, the mesh generation balances accuracy and efficiency, specifically including:

[0035] The central conductor / shielding layer has a small skin depth and a fine hexahedral / sweeped grid to ensure grid resolution within the skin layer.

[0036] The insulation layer is large in size and has low loss. It uses a free tetrahedral mesh, which is refined to capture temperature gradients.

[0037] In some possible implementations, the boundary condition setting including the first voltage specifically includes:

[0038] The settings include the lead port excitation voltage (i.e., the first voltage U2), load impedance, and port temperature. Specifically, these settings include: input port ( Figure 2 Left Port 1) is set to a 50Ω AC voltage source excitation voltage U2; output port ( Figure 2 Port 2 on the right is set to a high-impedance load (MΩ to GΩ) to simulate the input impedance of the voltmeter of the instrument under test. The input temperature is set to 4K and the output temperature is set to 20℃ (293.15K).

[0039] In some possible implementations, the coupling solution yields the target voltage, specifically including:

[0040] Magnetic field frequency domain analysis was performed to calculate the impedance, attenuation, and reflection characteristics of the coaxial cable at different frequencies.

[0041] Steady-state heat transfer analysis was performed to simulate the temperature distribution of the coaxial cable due to conductor loss and dielectric loss.

[0042] The Seebeck effect coupling is used to calculate the voltage superimposed on the electromagnetic signal by combining the temperature gradient and the Seebeck coefficient of the material.

[0043] The output voltage of the cable, i.e., the target voltage, is obtained through the above three analyses.

[0044] In some possible implementations, the boundary conditions of the first voltage are reset based on whether the target voltage is the value of the AC voltmeter being calibrated, until the target voltage is satisfied as the value of the AC voltmeter being calibrated. Specifically, this includes:

[0045] Determine whether the voltage at the output end of the lead wire is the value of the AC voltmeter being calibrated, i.e., the target voltage. If so, the excitation voltage at the lead wire port is the required theoretical modulation voltage value.

[0046] If not, return to the boundary condition setting step including the first voltage, and repeat the boundary condition setting until the target voltage is the value of the calibrated AC voltmeter.

[0047] This invention provides an AC voltage measurement method with lead error correction. It utilizes finite element analysis (finite element simulation software) to calculate theoretical waveform parameters, encodes the theoretical waveform information using ternary data codes, and generates a microwave pulse signal to excite the Josephson junction. This enables the Josephson junction of the pulse-driven quantum voltage system to produce a high-accuracy quantum voltage signal, which is then transmitted to the instrument under test, achieving high-accuracy AC voltage signal measurement for room-temperature instruments. This method is based on quantum physics and multiphysics coupling, employing numerical analysis to compensate for system errors caused by lead errors during the value transmission process in the pulse-driven quantum voltage system, reaching up to hundreds of microvolts, thus improving the accuracy of AC voltage measurement. While the theoretical parameters are generally amplitude and frequency, the focus is on the accuracy of the amplitude; lead error correction also corrects for the amplitude.

[0048] In summary, the measurement method of this application effectively addresses the problem that the accuracy of the output voltage of a pulse-driven quantum voltage system decreases sharply with increasing synthesis frequency, and the problem that the output voltage of the pulse-driven quantum voltage system is submerged in thermoelectric potential when measuring weak signals. This improves the measurable voltage range of the pulse-driven quantum voltage system and enhances measurement accuracy. It enables high-accuracy measurements of AC voltmeters, AC reference standards, and the like. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the measurement method flow;

[0050] Figure 2 This is a model of the output voltage of the quantum voltage system to the output lead of the instrument being measured in this measurement method;

[0051] Figure 3 This is a flowchart of the finite element analysis process;

[0052] Figure 4 Cable size parameters;

[0053] In the diagram: 1 - Josephson matching impedance, 2 - input impedance of the instrument under test, Port1 - input port, Port2 - output port. Detailed Implementation

[0054] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0055] Example 1

[0056] This embodiment provides an AC voltage measurement method with lead error correction, such as... Figure 1 As shown, it includes the following steps:

[0057] Step S1: Determine the target voltage U1 of the AC voltmeter being measured, which is the instrument being measured in this embodiment. Generally, it is the standard voltage of the AC voltmeter being measured.

[0058] Step S2: Calculate the theoretical modulation voltage value required by the AC voltmeter to be measured. The theoretical modulation voltage value is the first voltage value U2, which specifically includes:

[0059] S21. The target voltage U1 is obtained by analyzing and acquiring it using finite element simulation software. The process for obtaining the target voltage U1 is as follows: Figure 3 As shown, it specifically includes:

[0060] S211. Simplify the modeling of the connection between the quantum voltage system and the leads, such as... Figure 2 As shown, the leads are modeled based on actual lead parameters; the lead input is connected to a Josephson junction in a quantum voltage system, which is simplified to a series connection of an ideal AC voltage source and a Josephson junction matching impedance (50Ω); the lead output is connected to the instrument under test, which can be simplified to a parallel connection of an ideal AC voltmeter and the instrument's input impedance; the leads are coaxial cables, consisting of a central conductor layer, an insulation layer, and a shielding layer. A geometric model is established based on the actual parameters of each part of the cable, such as... Figure 4 As shown.

[0061] S212. Set the lead material properties, including temperature-dependent electrical / thermal / thermoelectric parameters. Assign temperature-dependent physical properties to each layer of material. For the central conductor layer, this includes electrical conductivity, which decreases with increasing temperature, but significantly increases to room temperature at 4K due to quantum confinement effects; thermal conductivity, specific heat capacity, density, and Seebeck coefficient. For the insulating material layer, this includes relative permittivity, volumetric conductivity, thermal conductivity, specific heat capacity, and Seebeck coefficient. For the shielding layer, this includes electrical conductivity, specific heat capacity, and Seebeck coefficient. When setting the electrical conductivity, the material's conductivity is set as a piecewise function related to temperature. A residual resistivity model is used at low temperatures, and a linear temperature coefficient model is used near room temperature.

[0062] S213. Multiphysics coupling configuration: Finite element simulation software analyzes and solves electromagnetic fields, heat transfer, and thermoelectric effects simultaneously, coupling electromagnetic and temperature fields for bidirectional coupled iterative solutions. Specifically, this includes:

[0063] Electromagnetic field analysis, based on Maxwell's equations, in frequency domain form, input port ( Figure 2 Left Port 1) is set to 50Ω AC voltage source excitation; output port ( Figure 2 Port 2 on the right is set as a high-resistance load (MΩ to GΩ) to simulate the input impedance of the voltmeter of the instrument under test. The electric field distribution and current density distribution of the coaxial cable are solved to obtain the conductor loss and dielectric loss. Based on Seebeck's equation, the Seebeck thermoelectric potential is solved. The thermoelectric potential generated by the Seebeck effect is superimposed on the electromagnetic field voltage as an additional potential.

[0064] Temperature field analysis was performed based on the Fourier heat conduction equation. The input temperature was set to 4K and the output temperature was set to 20℃ (293.15K). Joule heating was used as the heat source to solve for the temperature distribution of the coaxial cable.

[0065] Feedback iteration is used to investigate how temperature changes affect the conductivity of the central conductor layer and the dielectric constant of the insulation material in the coaxial cable. The iteration parameters are bidirectionally coupled and iterated until convergence. These parameters include temperature, conductivity, and dielectric constant. The iterative solution yields the output voltage of the conductor, determining the target voltage for the AC voltmeter being measured.

[0066] S214. Mesh generation balances accuracy and efficiency, specifically including: the central conductor / shielding layer, with a small skin depth, requires a fine hexahedral / sweeped mesh to ensure mesh resolution within the skin layer (at least 2-3 layers covering the skin depth); the insulating layer, with a large size and low loss, uses a free tetrahedral mesh, refined to capture temperature gradients.

[0067] S215, Boundary condition settings, including setting the lead port excitation voltage (i.e., the first voltage U2), load impedance settings, and port temperature settings, specifically including: input port ( Figure 2Left Port 1) is set to a 50Ω AC voltage source excitation voltage U2; output port ( Figure 2 Port 2 on the right is set to a high-impedance load (MΩ to GΩ) to simulate the input impedance of the voltmeter of the instrument under test. The input temperature is set to 4K and the output temperature is set to 20℃ (293.15K).

[0068] S216. The target voltage U1 is obtained through coupling solution, specifically including:

[0069] Magnetic field frequency domain analysis is used to calculate the impedance, attenuation, and reflection characteristics of coaxial cables at different frequencies.

[0070] Steady-state heat transfer analysis simulates the temperature distribution of a coaxial cable due to conductor and dielectric losses.

[0071] The Seebeck effect coupling is used to calculate the voltage superimposed on the electromagnetic signal by combining the temperature gradient and the Seebeck coefficient of the material.

[0072] The output voltage of the conductor (cable) is obtained through the above three analyses.

[0073] S217. Read the output voltage of the wire (cable): Determine whether the output voltage of the wire is the value of the AC voltmeter being calibrated, i.e., the target voltage U1. If so, the excitation voltage U2 of the lead port is the required theoretical modulation voltage value. If not, return to step S215 and reset the boundary conditions until the target voltage is the value of the AC voltmeter being calibrated.

[0074] The output voltage U1 of the cable is the actual voltage output to the instrument under test. By adjusting the excitation voltage at the input of the Josephson junction, the output voltage of the cable is made equal to the target voltage U1 of the instrument under test. The excitation voltage applied at the input of the Josephson junction at this time is the modulation theoretical voltage value, also known as the first voltage U2.

[0075] The reliability of the simulation model is determined by comparing the consistency between the output voltage calculated by finite element analysis and the voltage value of the instrument under test during actual measurement. This includes:

[0076] 1. Find a high-accuracy AC voltmeter to verify the simulation model. The simulation model and the actual measurement results should be consistent (the degree of consistency can be judged based on the instrument's allowable error limit).

[0077] 2. Find another high-accuracy AC voltage source to measure the AC voltmeter under test. Then compare the measurement results after the simulation model is corrected with the measurement results of the other high-accuracy source to determine whether the results meet the requirements.

[0078] This embodiment uses finite element analysis (finite element simulation software) to simulate the quantum voltage output link from the Josephson junction of the quantum voltage system to the instrument under test. Taking into account lead length, lead temperature variations, and the change in output voltage with the synthesis frequency, the excitation voltage at the Josephson junction input, i.e., the first voltage U2 (U2 = U1 + ΔU, where ΔU is the voltage component (voltage correction amount) caused by lead error), is calculated when the voltage U1 at the connection point between the lead and the instrument under test reaches the target voltage. The theoretical modulation voltage value U2 is used as the desired synthesized waveform, and Δ-Σ modulation is used to modulate the desired synthesized waveform into a... A series of digital codes are stored in a pulse code generator and converted into corresponding high-speed pulses. The high-speed pulses drive the Josephson junction in the liquid helium temperature range to generate a quantum voltage pulse sequence containing the waveform information to be synthesized, which excites the Josephson junction to generate a high-accuracy quantum voltage signal. The quantization noise is filtered out by a low-pass filter, and the filtered Josephson junction terminal voltage signal is the desired synthesized voltage waveform U2. After U2 is transmitted to the instrument under test through a lead, the obtained voltage is the target voltage U1, realizing the measurement of high-accuracy AC voltage signals of room temperature instruments and equipment.

[0079] The core physical effects that cause lead wire errors are mainly:

[0080] 1. Distributed parameters and attenuation: High-frequency signals are transmitted in coaxial cables as TEM waves. Distributed resistance (conductor skin effect, material loss), distributed inductance, distributed capacitance, and distributed conductance (dielectric loss) need to be considered. These factors will cause signal amplitude attenuation (α) and phase shift (β).

[0081] 2. Wave reflection: When the input impedance is mismatched with the output load, a reflection coefficient Γ is generated, resulting in the voltage along the line being the superposition of the incident wave and the reflected wave (standing wave distribution).

[0082] 3. Seebeck effect: The temperature difference between the two ends of the cable (4K→20℃) causes a thermoelectric potential between different material layers (center conductor, shielding layer). It is necessary to couple the thermal field and electric field to analyze the contribution of temperature distribution to Seebeck voltage.

[0083] To calculate voltage changes caused by leads in finite element analysis, it is necessary to couple the three major physical fields of electromagnetic, thermal, and thermoelectric (Seebeck effect), and consider factors such as cable attenuation, distributed parameters, and wave reflection.

[0084] Step S3: Δ-Σ modulation of the waveform of the first voltage U2 (modulation theoretical voltage value). Based on the target voltage U1 and the excitation voltage applied at the input terminal of the Josephson junction obtained in step S2, which is the modulation theoretical voltage value, also known as the first voltage U2, as the desired waveform, the waveform of the desired first voltage U2 is modulated into a series of digital codes using Δ-Σ modulation; the digital codes are stored in the pulse code generator and converted into corresponding high-speed pulses.

[0085] Step S4: The quantum voltage system outputs a first voltage U2 through the Josephson junction. The Josephson junction of the quantum voltage system is driven by high-speed pulses to generate a quantum voltage pulse sequence containing the U2 waveform information of the desired synthesized first voltage.

[0086] By using a low-pass filter, the quantization noise carried by the waveform of the first voltage U2 to be synthesized is filtered out;

[0087] The quantum voltage system outputs the first voltage signal U2 through the Josephson junction, which is the voltage waveform that is expected to be synthesized.

[0088] Step S5: The first voltage U2 is transmitted to the instrument under test through the lead wire. During the transmission process, a portion of the voltage is diverted by the lead wire, which is the voltage correction amount ΔU. The final voltage obtained is the target voltage U1.

[0089] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A method for measuring AC voltage with lead error correction, characterized in that, Includes the following steps: The target voltage was obtained by analyzing the data using finite element simulation software. The first voltage is adjusted according to the target voltage value, and the desired synthesized first voltage waveform is modulated into a series of digital codes using Δ-Σ modulation. The digital code pattern is stored in the pulse code generator and converted into a corresponding high-speed pulse; By using high-speed pulses to drive the Josephson junction of a quantum voltage system, a quantum voltage pulse sequence containing waveform information of the desired first voltage is generated. The quantum voltage system outputs a first voltage signal through the Josephson junction, which is the voltage waveform to be synthesized. The first voltage is transmitted to the instrument under test through the lead wire, and the obtained voltage is the target voltage.

2. The AC voltage measurement method with lead error correction according to claim 1, characterized in that, Before the quantum voltage system outputs the first voltage signal through the Josephson junction, it also includes filtering out the quantization noise carried by the waveform of the desired synthesized first voltage by passing a low-pass filter.

3. The AC voltage measurement method with lead error correction according to claim 1 or 2, characterized in that, The method of using finite element simulation software to analyze and obtain the target voltage specifically includes: The connection between the quantum voltage system and the leads is simplified and modeled, while the leads are modeled based on actual lead parameters. Set the lead material properties, including temperature-related electrical / thermal / thermoelectric parameters, and assign temperature-dependent physical properties to each layer of material; Multiphysics coupling configuration, finite element simulation software analyzes and solves electromagnetic field, heat transfer, thermoelectric effect simultaneously, coupled electromagnetic field, temperature field and electric field, and performs bidirectional coupled iterative solution; Mesh generation strikes a balance between accuracy and efficiency; This includes setting the boundary conditions for the first voltage; The target voltage is obtained by coupling solution; If the target voltage is not the same as the value of the AC voltmeter being calibrated, the boundary conditions of the first voltage are reset until the target voltage is the same as the value of the AC voltmeter being calibrated.

4. The AC voltage measurement method with lead error correction according to claim 3, characterized in that, The simplified modeling of the connection between the quantum voltage system and the leads, with the leads modeled according to actual lead parameters, specifically includes: The lead input terminal is connected to the Josephson junction of the quantum voltage system. The Josephson junction is simplified to a series connection of an ideal AC voltage source and the Josephson junction matching impedance. The lead output terminal is connected to the instrument under test. The instrument under test can be simplified to a parallel connection of an ideal AC voltmeter and the input impedance of the instrument under test. The lead wire is a coaxial cable, consisting of three layers: a central conductor layer, an insulation material layer, and a shielding layer. A geometric model is established based on the actual parameters of each part of the cable.

5. The AC voltage measurement method with lead error correction according to claim 4, characterized in that, The setting of lead material properties, including temperature-related electrical / thermal / thermoelectric parameters, and the assignment of temperature-dependent physical properties to each layer of material, specifically includes: Central conductor layer: electrical conductivity, which decreases with increasing temperature, and at 4K the conductivity is significantly higher than that at room temperature due to the quantum confinement effect; thermal conductivity, specific heat capacity, density, Seebeck coefficient; Insulating material layer: relative permittivity, volume conductivity, thermal conductivity, specific heat capacity, Seebeck coefficient; Shielding layer: conductivity, specific heat capacity, Seebeck coefficient.

6. The AC voltage measurement method with lead error correction according to claim 3, characterized in that, The aforementioned multiphysics coupling configuration allows finite element simulation software to simultaneously analyze and solve for electromagnetic fields, heat transfer, and thermoelectric effects. It couples the electromagnetic field with the temperature field, performing a bidirectional coupled iterative solution, specifically including: Electromagnetic field analysis, based on Maxwell's equations in the frequency domain, is performed with the input port set to a 50Ω AC voltage source for excitation and the output port set to a high-impedance load to simulate the input impedance of the instrument under test. The electric field distribution and current density distribution of the coaxial cable are solved to obtain the conductor loss and dielectric loss. Temperature field analysis was performed based on the Fourier heat conduction equation. The input temperature was set to 4K and the output temperature was set to 20℃. Joule heating was used as the heat source to solve for the temperature distribution of the coaxial cable. Electric field analysis, based on Seebeck's equations, solves for the Seebeck thermoelectric potential. The thermoelectric potential generated by the Seebeck effect is superimposed on the electromagnetic field voltage as an additional potential. Feedback iteration: Temperature changes affect the conductivity of the central conductor layer of the coaxial cable and the dielectric constant of the insulating material. The parameters are iterated through bidirectional coupling until convergence.

7. The AC voltage measurement method with lead error correction according to claim 5, characterized in that, The mesh generation balances accuracy and efficiency, specifically including: The central conductor / shielding layer has a small skin depth and a fine hexahedral / sweeped grid to ensure grid resolution within the skin layer. The insulation layer is large in size and has low loss. It uses a free tetrahedral mesh, which is refined to capture temperature gradients.

8. The AC voltage measurement method with lead error correction according to claim 3, characterized in that, The boundary condition setting, including the first voltage, specifically includes: The settings for lead port excitation voltage (i.e., the first voltage U2), load impedance, and port temperature include: setting the input port to a 50Ω AC voltage source excitation voltage U2; setting the output port to a high-impedance load to simulate the input impedance of the voltmeter of the instrument under test; setting the input temperature to 4K; and setting the output temperature to 293.15K.

9. The AC voltage measurement method with lead error correction according to claim 3, characterized in that, The coupling solution yields the target voltage, specifically including: Magnetic field frequency domain analysis was performed to calculate the impedance, attenuation, and reflection characteristics of the coaxial cable at different frequencies. Steady-state heat transfer analysis was performed to simulate the temperature distribution of the coaxial cable due to conductor loss and dielectric loss. The Seebeck effect coupling is used to calculate the voltage superimposed on the electromagnetic signal by combining the temperature gradient and the Seebeck coefficient of the material. The output voltage of the cable, i.e., the target voltage, is obtained through the above three aspects of analysis.

10. The AC voltage measurement method with lead error correction according to claim 3, characterized in that, The determination of whether the target voltage matches the value of the AC voltmeter being calibrated involves resetting the boundary conditions of the first voltage until the target voltage matches the value of the AC voltmeter being calibrated. Specifically, this includes: Determine whether the voltage at the output end of the lead wire is the value of the AC voltmeter being calibrated, i.e., the target voltage. If so, the excitation voltage at the lead wire port is the required theoretical modulation voltage value. If not, return to the boundary condition setting step including the first voltage, and repeat the boundary condition setting until the target voltage is the value of the calibrated AC voltmeter.

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