CN-121978390-A - Alternating-current voltage measuring method for lead error correction

CN121978390ACN 121978390 ACN121978390 ACN 121978390ACN-121978390-A

Abstract

The invention discloses an alternating voltage measuring method for lead error correction, which comprises the following steps of adopting finite element simulation software to analyze and obtain voltage correction quantity caused by lead error, adding the voltage correction quantity to target voltage to obtain first voltage based on the target voltage, modulating a first voltage waveform expected to be synthesized into a series of digital code patterns by delta-sigma modulation, storing the digital code patterns into a pulse code pattern generator and converting the digital code patterns into corresponding high-speed pulses, driving a Josephson junction of a quantum voltage system by utilizing the high-speed pulses to generate a quantum voltage pulse sequence containing waveform information of the first voltage expected to be synthesized, outputting a first voltage signal through the Josephson junction end by the quantum voltage system, namely, transmitting the first voltage to a measured instrument through a lead, and obtaining the voltage which is the target voltage. The invention calculates the lead error by a finite element analysis method and reduces the influence of the lead error.

Inventors

ZHANG LIDAN
KANG YAN
ZHU ZHU

Assignees

北京无线电计量测试研究所

Dates

Publication Date: 20260505
Application Date: 20251226

Claims (10)

1. The alternating voltage measuring method for lead error correction is characterized by comprising the following steps: Analyzing and obtaining target voltage by adopting finite element simulation software; adjusting the first voltage according to the target voltage value, and modulating the first voltage waveform expected to be synthesized into a series of digital code patterns by delta-sigma modulation; Storing the digital code pattern into a pulse code pattern generator and converting the digital code pattern into corresponding high-speed pulses; Driving a Josephson junction of a quantum voltage system with high-speed pulses to generate a quantum voltage pulse train containing waveform information of a desired synthesized first voltage; the quantum voltage system outputs a first voltage signal, namely a voltage waveform expected to be synthesized, through the Josephson junction terminal; the first voltage is transmitted to the tested instrument through the lead, and the obtained voltage is the target voltage.
2. The method for measuring the alternating voltage corrected by the lead error according to claim 1, wherein before the quantum voltage system outputs the first voltage signal through the josephson junction terminal, the method further comprises filtering quantization noise carried by the waveform of the first voltage expected to be synthesized through low-pass filtering.
3. The method for measuring an ac voltage with corrected lead error according to claim 1 or 2, wherein the step of obtaining the target voltage by finite element simulation software analysis comprises: simplifying modeling is carried out on connection between the quantum voltage system and the lead, and the lead is modeled according to actual lead parameters; setting lead material properties, including temperature-dependent electrical/thermal/thermoelectric parameters, and distributing temperature-dependent physical properties to each layer of material; The multi-physical field coupling configuration is carried out, the finite element simulation software analyzes and solves electromagnetic fields, heat transfer and thermoelectric effects simultaneously, couples the electromagnetic fields, temperature fields and electric fields, and carries out bidirectional coupling iterative solution; Performing grid division to balance accuracy and efficiency; Boundary condition settings including a first voltage; Obtaining a target voltage by coupling solution; Whether the target voltage is the calibrated AC voltmeter value or not is judged, and the boundary condition of the first voltage is reset until the target voltage is the calibrated AC voltmeter value.
4. The method for measuring an ac voltage with corrected lead error according to claim 3, wherein the simplified modeling of the connection between the quantum voltage system and the lead is performed by modeling the lead according to actual lead parameters, specifically comprising: The lead input end is connected to the Josephson junction of the quantum voltage system, the Josephson junction is simplified into a series connection of an ideal alternating voltage source and the matching impedance of the Josephson junction, the lead output end is connected to a tested instrument, and the tested instrument can be simplified into a parallel connection of an ideal alternating voltage meter and the input impedance of the tested instrument; The lead is a coaxial cable and is divided into a central conductor layer, an insulating material layer and a shielding layer, and a geometric model is built according to actual parameters of each part of the cable.
5. The method for measuring an ac voltage with corrected lead error according to claim 4, wherein said setting of lead material properties, including temperature dependent electrical/thermal/thermoelectric parameters, assigns temperature dependent physical properties to each layer of material, specifically comprises: the central conductor layer is characterized in that the electric conductivity is reduced along with the temperature rise, and the electric conductivity is obviously higher than the room temperature due to the quantum confinement effect at 4 k; an insulating material layer, namely a relative dielectric constant, a volume electrical conductivity, a thermal conductivity, a specific heat capacity and a Seebeck coefficient; And the shielding layer is conductive, specific heat capacity and Seebeck coefficient.
6. The method for measuring ac voltage with corrected lead error according to claim 3, wherein the multi-physical field coupling configuration, the finite element simulation software analysis simultaneously solves electromagnetic field, heat transfer, thermoelectric effect, couples electromagnetic field and temperature field, and performs bi-directional coupling iterative solving, specifically comprising: the electromagnetic field analysis is based on a Maxwell equation set, the frequency domain form is adopted, the input port is set to be excited by a 50Ω alternating current voltage source, the output port is set to be a high-resistance load, the input impedance of a tested instrument is simulated, the electric field distribution and the current density distribution of the coaxial cable are solved, and the conductor loss and the dielectric loss are obtained; temperature field analysis, namely, based on a Fourier heat conduction equation, setting the temperature at 4K at an input end and 20 ℃ at an output end, and solving the temperature distribution of the coaxial cable by taking Joule heat as a heat source; Electric field analysis, solving the seebeck thermoelectric potential based on the seebeck equation, wherein the thermoelectric potential generated by the seebeck effect is used as an additional potential to be superimposed into the electromagnetic field voltage; And (3) feedback iteration, wherein the temperature change influences the conductivity of the central conductor layer of the coaxial cable and the dielectric constant of the insulating material, and iteration parameters are iterated through bidirectional coupling until convergence.
7. The method for measuring an ac voltage with corrected lead error according to claim 5, wherein said meshing is performed with a balance between accuracy and efficiency, and specifically comprises: The central conductor/shielding layer has small skin depth and fine hexahedron/sweep grid, so that the grid resolution in the skin-seeking layer is ensured; the insulating layer has large size and low loss, and adopts a free tetrahedral grid for refining to capture the temperature gradient.
8. The method for measuring an ac voltage with corrected lead error according to claim 3, wherein the boundary condition setting including the first voltage specifically includes: the lead port excitation voltage, namely the first voltage U2, the load impedance and the port temperature are set, and specifically comprises the input port set to be 50 omega alternating current voltage source excitation voltage U2, the output port set to be high-resistance load, the input impedance of a voltmeter of a tested instrument is simulated, the input end set to be 4K, and the output end set to be 293.15K.
9. The method for measuring an ac voltage with corrected lead error according to claim 3, wherein said coupling solution obtains a target voltage, specifically comprising: Analyzing the frequency domain of the magnetic field, and calculating the impedance, attenuation and reflection characteristics of the coaxial cable at different frequencies; Steady state heat transfer analysis, simulating the temperature distribution of the coaxial cable due to conductor loss and dielectric loss; seebeck effect coupling, combining the temperature gradient and the Seebeck coefficient of the material, and calculating the voltage of the thermoelectric voltage superimposed on the electromagnetic signal; and obtaining the output terminal voltage of the cable through the analysis of the three aspects, namely the target voltage.
10. The method for measuring an ac voltage with corrected lead error according to claim 3, wherein the step of resetting the boundary condition of the first voltage until the target voltage is satisfied, if the target voltage is a calibrated ac voltmeter value, comprises: Judging whether the voltage of the output end of the lead is a calibrated alternating-current voltmeter value, namely a target voltage, and if so, judging that the excitation voltage of the lead port is a required modulation theoretical voltage value; if not, returning to the boundary condition setting step including the first voltage, and re-performing the boundary condition setting until the target voltage is satisfied as the calibrated AC voltmeter value.

Description

Alternating-current voltage measuring method for lead error correction Technical Field The invention relates to the technical field of quantized low-frequency voltage, in particular to an alternating-current voltage measuring method for lead error correction. Background The pulse driving type quantum voltage system adopts a series of high-speed current pulses to drive the Josephson junction array according to the magnetic flux quantum principle, and the Josephson junction array generates corresponding magnetic flux quanta with the time integration area being equal to h/(2 e) after being driven, and the alternating current voltage waveform can be synthesized through filtering. The process of synthesizing voltage waveforms by pulse-driven Josephson voltage standard includes such steps as modulating desired synthesized waveform to a series of digital codes by delta-sigma modulation, storing the digital codes in pulse code generator, converting them to high-speed pulses, and high-speed pulse driving Josephson junction array to generate quantum voltage pulse sequence containing waveform information. These quantum voltage pulses are replicas of the delta-sigma modulated digital pattern, filtering out the carried quantization noise by low pass filtering. The voltage signal obtained after filtering is the voltage waveform required to be synthesized. Since the quantum voltages generated from the josephson junction array need to be transferred to the instrument under test, typically a calibrated ac voltmeter, via the output link of the pulse-driven quantum voltage system, the magnitude of the voltages transferred to the instrument under test is not exactly equal to the magnitude of the quantum voltages generated by the josephson junction array. The main cause of the error is resonance in the loop caused by inductance and capacitance on the quantum voltage output lead, and thermoelectric potential caused by temperature change from the liquid helium temperature region to room temperature. Since the quantum voltage is generated at low temperature and the measuring instrument is in a room temperature environment, this results in the influence of a longer voltage lead connected to the load and possibly to the high frequency loop being a major component of uncertainty, the maximum extent of influence being up to three to four orders of magnitude. When the synthesized quantum voltage frequency reaches MHz, the main error source is voltage lead error. At present, lead errors are reduced mainly by reducing the length of the internal lead of a low-temperature test probe rod, reducing the length of a test wire at a room temperature end, improving a cable processing technology and the like as far as possible when a pulse-driven quantum voltage system is designed, but the lead length cannot be very small due to the operation requirement of the whole system, so that the influence of the lead errors cannot be well reduced by the method. It is needed to propose a correction method of lead error and an ac voltage measurement method, which reduce the influence of the lead error on measurement. Disclosure of Invention The invention aims to provide an alternating current voltage measurement method for correcting lead errors, which is used for solving the problem of reduced accuracy of signals output by a pulse-driven quantum voltage system caused by the lead errors, adopts a finite element analysis technology to carry out theoretical calculation on errors generated by the lead of the pulse-driven quantum voltage system by using finite element simulation software, and corrects the errors in the operation of the pulse-driven quantum voltage system, so that the influence of the lead errors on measurement is reduced, and the accuracy of alternating current voltage measurement is higher. In order to achieve the above purpose, the invention adopts the following technical scheme: In a first aspect, the present invention provides a method for measuring an ac voltage with corrected lead error, including the steps of: Analyzing and obtaining target voltage by adopting finite element simulation software; Adjusting a first voltage (i.e. a josephson junction input excitation voltage) according to the target voltage, modulating a first voltage waveform desired to be synthesized into a series of digital patterns using delta-sigma modulation; Storing the digital code pattern into a pulse code pattern generator and converting the digital code pattern into corresponding high-speed pulses; Driving a Josephson junction of a quantum voltage system with high-speed pulses to generate a quantum voltage pulse train containing waveform information of a desired synthesized first voltage; the quantum voltage system outputs a first voltage signal, namely a voltage waveform expected to be synthesized, through the Josephson junction terminal; the first voltage is transmitted to the tested instrument through the lead, and the obtained voltage is the target voltage. In