A current ratio standard self-calibration method without external standard source

Abstract

The application discloses a current proportion standard self-calibration method without external standard source, which is applied to a current proportion standard device composed of a first-stage fixed proportion current comparator and a second-stage variable proportion current comparator. The method completes full-range calibration of the first-stage comparator through series-parallel connection method, including lowest-range winding series calibration, intermediate-range winding step-by-step recursive calibration and highest-range and reference winding calibration; the second-stage comparator adopts a calibration mechanism combining internal winding replacement difference and whole equal-turn number comparison, establishes relative relationship between windings and solves equivalent parameters. The application realizes self-calibration through built-in current source without external standard source, reduces calibration cost and period, avoids artificial operation uncertainty, and makes current proportion error of each gear less than ±0.2 ppm, effectively improving measurement consistency and long-term operation stability.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic metering technology, specifically relating to a self-calibration method for a current ratio standard without an external standard source for DC power metering traceability. It is applicable to the internal closed-loop calibration of a two-stage cascaded current ratio standard device and can be adapted to DC current metering scenarios in new power systems such as UHVDC transmission, DC charging of electric vehicles, and photovoltaic power generation and energy storage. Background Technology

[0002] The application of DC power in new power systems is rapidly expanding towards higher voltage, higher current, and wider measurement ranges. As the core equipment for transmitting DC current values, the accuracy and long-term stability of the current proportional standard device directly determine the reliability of DC power metering traceability.

[0003] Traditional calibration methods for current proportional standards typically rely on external references such as external standard sources, standard windings, and standard comparators, which have the following significant drawbacks: The calibration process requires the introduction of external standards, which makes the calibration system complex, costly, and inconvenient to carry. External standard sources themselves have temperature drift, time drift, and linearity errors, which directly introduce calibration uncertainty. The cascaded errors between multi-stage current comparators cannot be uniformly corrected under the same reference. The calibration process relies on manual operation, has a low degree of automation, and poor repeatability; It is impossible to achieve online self-calibration and real-time error correction of the device.

[0004] Furthermore, existing self-calibration schemes are mostly designed for single-stage current comparators, enabling only simple calibration of local windings. They cannot be adapted to two-stage cascaded wide-range current proportional standard devices, and some schemes still rely on external small-current standard sources for reference, failing to achieve truly "external standard source-free" complete internal calibration. This makes it difficult to meet the requirements of wide-range, high-accuracy DC energy metering traceability. Therefore, there is an urgent need for a self-calibration method that requires no external standard source, external standard windings, or external standard devices, is compatible with two-stage cascaded structures, and can automatically complete calibration across all ranges, thus overcoming the aforementioned shortcomings of existing technologies. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a self-calibration method for current ratio standards without an external standard source, without an external standard source, external standard winding, or external standard device, and adapted to a two-stage cascaded structure, which can automatically complete the calibration of all ranges.

[0006] To achieve the above-mentioned objectives, this invention provides a self-calibration method for a current ratio standard without an external standard source, which is applied to a current ratio standard device composed of a first-stage fixed-ratio current comparator and a second-stage variable-ratio current comparator cascaded in proportion. The primary winding of the first-stage current comparator includes a first reference winding and multiple switching winding arrays for different ranges; each switching winding array contains several first winding units with the same number of turns, and the switching winding arrays for adjacent ranges increase or decrease according to a fixed ratio; the secondary winding of the first-stage current comparator is a winding with a fixed number of turns; the number of turns of the first reference winding is the same as the number of turns of the winding unit of the highest range switching winding array in the first-stage current comparator; The primary winding of the second-stage current comparator includes at least one set of second reference windings and multiple freely combinable subdivision winding units; the number of turns of each subdivision winding unit is distributed sequentially according to a preset weighting rule, and can form any target number of turns through the series combination of different winding units; the secondary winding of the second-stage current comparator is also a fixed number of turns winding, and its number of turns is the same as that of the secondary winding of the first-stage current comparator; the number of turns of the second reference winding is the same as the number of turns of the highest range subdivision winding unit in the second-stage current comparator; and the number of turns of the lowest range subdivision winding unit in the second-stage current comparator is less than the number of turns of the secondary winding of the second-stage current comparator. The method includes two-stage calibration: a first-stage current comparator calibration and a second-stage current comparator calibration. The order of the first-stage current comparator calibration and the second-stage current comparator calibration is not limited. The first-stage current comparator is calibrated using a series-parallel method, specifically including: S11. Lowest range winding series calibration: Connect all winding units corresponding to the lowest range setting in series to form a series combined winding; connect this series combined winding in reverse parallel with a secondary winding with a fixed number of turns, and use an ampere-turn meter in the secondary winding circuit to measure the difference in magnetomotive force between the series combined winding and the secondary winding to establish an equation relationship. S12. Intermediate range winding stepwise calibration: Switch all winding units of the calibrated previous range winding to a parallel state to form a previous parallel winding; connect the current next range winding to be calibrated in series to form a next series winding; then connect the previous parallel winding and the next series winding in reverse series to close the circuit, and use the ampere-turn meter in the secondary winding circuit to measure the difference in magnetomotive force between the previous parallel winding and the next series winding to establish the proportional relationship between the two range windings. Repeat the above recursive process in order from low range to high range to complete the calibration of all intermediate range windings in sequence. S13. Calibration of the highest range winding and the reference winding: Connect the winding unit of the highest range to the preset first reference winding in reverse series. Through the induction of the primary winding and the secondary winding, use the ampere-turn meter of the secondary winding circuit to measure the difference in magnetomotive force between the winding unit of the highest range and the first reference winding to establish the equation relationship between the lowest range winding and the reference winding. Throughout the calibration process from S11 to S13, a fixed number of turns of the secondary winding is used as a unified reference. The measurement signals of the ampere-turn meter of the secondary winding circuit are collected, and the equations of the magnetomotive force difference between the windings are established in each calibration process. The equations are solved and the proportional error of each winding unit under different series and parallel combination states is corrected to complete the proportional calibration of the first-stage current comparator under the full range and full combination state. The two-stage calibration of the secondary comparator includes: The first level involves internal winding replacement and differential self-calibration: each subdivided winding unit to be calibrated in the second-level current comparator is selected sequentially, and current is passed in reverse to the second reference winding at the corresponding terminals. The difference in magnetomotive force between the subdivided winding unit to be calibrated and the second reference winding is measured by the ampere-turn meter in the secondary winding circuit. Based on the results of multiple replacement measurements, a set of equations reflecting the equivalent parameter deviation relationship between each subdivided winding unit to be calibrated and the second reference winding is established until the measurement of all subdivided winding units to be calibrated is completed, forming a solvable set of equations. The second level involves the overall self-calibration of the primary winding against the secondary winding for equal turns: The subdivided windings of the second-stage current comparator are connected in series to form a primary combined winding, ensuring that the total equivalent turns on the primary side are equal to the nominal turns of the secondary winding, thus establishing an equal turns condition. The primary combined winding with the equal turns condition is then connected in reverse parallel with the secondary winding. The difference in magnetomotive force between the primary combined winding and the secondary winding is measured using an ammeter in the secondary winding circuit to obtain the equal turns comparison result. The relative relationship between the windings obtained in the first level is combined with the equal turns comparison result to calculate the equivalent parameters of each subdivided winding unit and the secondary winding, completing the overall self-calibration.

[0007] Furthermore, the series-parallel calibration of the first-level comparator and the two-level calibration of the second-level comparator are both automatically executed by the control system through a proportional switching actuator, and a closed-loop calibration is formed through measurement, calculation, and parameter updating. The control system includes a host computer, a controller, and a proportional switching actuator. The host computer is used to store measurement data, establish and solve a set of equations, and generate correction coefficients. The controller is any one of a programmable logic controller, an industrial control computer, an embedded controller, or a microcontroller. The controller is communicatively connected to the host computer and the proportional switching actuator, respectively, and receives instructions from the host computer and controls the actuator to act according to a preset timing sequence. The proportional switching actuator is any one of a relay matrix, a magnetic latching relay array, or a solid-state relay array. The actuator is electrically connected to the winding of the two-stage current comparator to realize the switching of the winding's on / off state, combination, and connection mode.

[0008] Furthermore, the first-stage fixed-proportion current comparator is a decimal current comparator; the primary winding of the first-stage fixed-proportion current comparator includes at least one first reference winding and multiple decimal switching windings of different magnitudes, each magnitude decimal switching winding includes 10 first winding units with the same number of turns, and the number of turns of the first winding units in any two adjacent magnitude decimal switching windings is changed according to the decimal magnitude; the number of turns of the first reference winding is the same as the number of turns of the decimal switching winding of the highest range; the number of turns of the secondary winding of the first-stage fixed-proportion current comparator is determined by the fixed proportion. The second-stage variable proportional current comparator is a binary current comparator; the primary winding of the second-stage variable proportional current comparator includes at least one set of second reference windings and multiple binary switching windings, each binary switching winding including one second winding unit, and the number of turns of each second winding unit is 2. n Distribution, where n is a continuous natural number; the number of turns of the second reference winding is the same as the number of turns of the binary switching winding of the highest range; the number of turns of the secondary winding of the second-stage variable proportional current comparator is the same as the number of turns of the secondary winding of the first-stage fixed proportional current comparator, and the number of turns of the second winding unit of the lowest range is smaller than the number of turns of the secondary winding of the second-stage variable proportional current comparator.

[0009] Furthermore, the fixed ratio includes 1:1, 1:10, 1:100, and 1:1000; In the first-stage current comparator, the first reference winding is a group with 1 turn; the number of decimal switching windings is 3, and the number of turns of the first winding unit in each decimal switching winding is 1 turn, 10 turns and 100 turns respectively. In the second-stage current comparator, the second reference winding is a group with 1 turn; n is a continuous natural number from 0 to 9; that is, the number of binary switching windings is 10, and the number of turns of the second winding unit is 1, 2, 4, 8, 16, 32, 64, 128, 256, and 512 turns respectively. The number of turns in the secondary winding of the first-stage current comparator and the secondary winding of the second-stage current comparator are both 1000 turns.

[0010] Furthermore, after the first-stage current comparator completes full-range calibration, it automatically generates a proportional error correction table for each range and stores it in the control system for real-time correction in subsequent measurements.

[0011] Furthermore, after completing two-stage calibration, the second-stage current comparator automatically generates an equivalent parameter table for each subdivided winding unit and substitutes the equivalent parameters into the current proportional calculation model to achieve real-time correction of the proportional output.

[0012] Furthermore, the first-stage current comparator and the second-stage current comparator share the same reference power supply, the same ampere-turn magnetomotive force measurement circuit, and the same sampling circuit.

[0013] Compared with the prior art, the programmable switching method for the two-stage cascaded current ratio of the present invention has the following significant advantages: (1) Completely independent of external standard sources, standard windings or external reference devices, achieving true zero-reference self-calibration: This invention adopts a technical solution of first-stage series-parallel calibration + second-stage internal winding replacement differential calibration + two-stage shared unified secondary winding reference. The entire process relies solely on the series and parallel combination and differential comparison of the internal windings of the device to complete the proportional error calibration in the full range, full range, and full combination state. It gets rid of the dependence on external standard sources, standard coils, and standard comparison devices, eliminates temperature drift, time drift, linearity error and installation error introduced by external references, and significantly reduces system complexity and calibration cost.

[0014] (2) The two-stage comparators share a unified secondary winding reference, resulting in high consistency in the transmission of values ​​and small system error: In this invention, the first-stage fixed ratio comparator and the second-stage variable ratio comparator share the same set of secondary windings as a unified reference, and share the same set of reference power supply, ampere-turn magnetomotive force measurement circuit and sampling circuit. The entire process is completed with a unified reference to collect, calculate and correct the ratio error, avoiding the cascading error and reference drift problem between multiple references. The value transmission chain is short, the consistency is high and the system error is small, effectively improving the overall accuracy and long-term stability of the current ratio standard device.

[0015] (3) The invention adopts a dual-mode calibration of series-parallel recursion and internal winding replacement, covering the full range, all gears, and all combination states: For the first-level fixed ratio comparator, the invention adopts a series-parallel recursive calibration scheme of the lowest range series calibration → intermediate range step-by-step recursion → comparison of the highest range with the reference winding; For the second-level variable ratio comparator, the invention adopts a two-level calibration scheme of internal winding replacement difference → overall equal number of turns comparison; The two schemes are independent of each other and can complement each other, covering all range gears and series and parallel combination states from the lowest range to the highest range and from the lowest range to the finest winding, realizing self-calibration in the full range, all gears, and all combination states.

[0016] (4) Fully automated closed-loop calibration without manual intervention, greatly improving calibration accuracy and repeatability: This invention automatically completes winding switching, proportional switching, current switching, data acquisition, equation solving and correction coefficient updating through "control system + proportional switching actuator", forming a closed-loop self-calibration system of measurement-solving-correction-re-measurement. It eliminates the need for manual wiring, manual comparison, and manual calculation, effectively avoiding random and systematic errors introduced by manual operation. The calibration process is highly automated, has good repeatability, and significantly improves calibration efficiency and accuracy.

[0017] (5) After calibration, a correction table and an equivalent parameter table are automatically generated to achieve real-time online error correction: After the first-level comparator is calibrated, a full-range range proportional error correction table is automatically generated; after the second-level comparator is calibrated, an equivalent parameter table and a proportional error model for each subdivision winding are automatically generated; both tables are stored in the control system in real time and can be directly used for real-time online proportional error correction in subsequent precision measurement and value transmission processes, further improving the output accuracy and stability of the device.

[0018] (6) The structure is simple, highly integrated, and highly applicable. It can be widely used in various fixed / variable proportional current standard devices. The technical solution of this invention does not require the addition of additional standard sources, standard windings or external calibration equipment. It can achieve self-calibration by relying solely on the series and parallel combination and differential comparison of the internal windings. The device has a simple structure, high integration, small size, and high applicability. It is also compatible with two-stage cascaded current proportional standard devices. For example, it is suitable for self-calibration scenarios of various two-stage cascaded current proportional standard devices, precision proportional transformers, and electromagnetic value transmission devices with multiple ranges in decimal and binary systems. It has extremely high versatility and practicality. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 This is a flowchart illustrating the overall process of the self-calibration method for the two-stage cascaded current ratio of the present invention.

[0021] Figure 2 This is a schematic diagram of the control system used to implement the method of the present invention.

[0022] Figure 3 This is a flowchart illustrating the control process of the control system in an embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram showing the content of a winding switching scheme and self-calibration results displayed by the host computer in an embodiment of the present invention.

[0024] Figure 5This is a schematic diagram of the primary and secondary windings of the first-stage fixed-proportion current comparator in a decimal system according to an embodiment of the present invention.

[0025] Figure 6 This is a schematic diagram of the primary and secondary windings of the binary second-stage variable proportional current comparator in an embodiment of the present invention.

[0026] Figure 7 This is a schematic diagram of the first-level calibration structure of the two-level calibration of the two-level comparator in an embodiment of the present invention.

[0027] Figure 8 This is a schematic diagram of the second-level calibration structure of the two-stage comparator in an embodiment of the present invention. Detailed Implementation

[0028] The present invention addresses the problem that existing current ratio standards generally rely on external high-current standard sources for step-by-step calibration, which is costly and time-consuming. It provides a self-calibration method for current ratio standards without external standard sources, external standard windings, or external standard devices, and is compatible with two-stage cascaded structures, and can automatically complete calibration of all ranges.

[0029] The overall concept of this invention is as follows: This invention provides a current ratio standard self-calibration method that requires no external standard source, is compatible with a two-stage cascaded structure, and can automatically complete calibration across all ranges. It is applied to a device consisting of a first-stage fixed-ratio current comparator (decimal) and a second-stage variable-ratio current comparator (binary) cascaded together. The method employs a two-stage calibration process: first-stage series-parallel calibration (including lowest range series calibration, intermediate range step-by-step recursive calibration, and highest range calibration with reference winding), and second-stage internal winding substitution difference and overall comparison. Using a fixed secondary winding as a unified reference, and combined with a control system, it automatically performs winding switching, data acquisition, and error correction. This achieves automated closed-loop self-calibration across all ranges and ranges without relying on an external standard source, and generates a correction table for real-time error correction.

[0030] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0031] Please see Figures 1 to 8 As shown, this embodiment of a current ratio standard self-calibration method without an external standard source is applied to a current ratio standard device composed of a first-stage fixed-ratio current comparator and a second-stage variable-ratio current comparator cascaded in proportion. The primary winding of the first-stage current comparator includes a first reference winding and multiple switching winding arrays for different ranges; each switching winding array contains several first winding units with the same number of turns, and the switching winding arrays for adjacent ranges increase or decrease according to a fixed ratio; the secondary winding of the first-stage current comparator is a winding with a fixed number of turns; the number of turns of the first reference winding is the same as the number of turns of the winding unit of the highest range switching winding array in the first-stage current comparator; The primary winding of the second-stage current comparator includes at least one set of second reference windings and multiple freely combinable subdivision winding units; the number of turns of each subdivision winding unit is distributed sequentially according to a preset weighting rule, and can form any target number of turns through the series combination of different winding units; the secondary winding of the second-stage current comparator is also a fixed number of turns winding, and its number of turns is the same as that of the secondary winding of the first-stage current comparator; the number of turns of the second reference winding is the same as the number of turns of the highest range subdivision winding unit in the second-stage current comparator; and the number of turns of the lowest range subdivision winding unit in the second-stage current comparator is less than the number of turns of the secondary winding of the second-stage current comparator. like Figure 1 As shown, the method includes two-stage calibration: a first-stage comparator calibration and a second-stage comparator calibration. The order of the first-stage current comparator calibration and the second-stage current comparator calibration is not limited. The first-stage current comparator is calibrated using a series-parallel method, specifically including: S11. Lowest range winding series calibration: Connect all winding units corresponding to the lowest range setting in series to form a series combined winding; connect this series combined winding in reverse parallel with a secondary winding with a fixed number of turns, and use an ampere-turn meter in the secondary winding circuit to measure the difference in magnetomotive force between the series combined winding and the secondary winding to establish an equation relationship. S12. Intermediate range winding stepwise calibration: Switch all winding units of the calibrated previous range winding to a parallel state to form a previous parallel winding; connect the current next range winding to be calibrated in series to form a next series winding; then connect the previous parallel winding and the next series winding in reverse series to close the circuit, and use the ampere-turn meter in the secondary winding circuit to measure the difference in magnetomotive force between the previous parallel winding and the next series winding to establish the proportional relationship between the two range windings. Repeat the above recursive process in order from low range to high range to complete the calibration of all intermediate range windings in sequence. S13. Calibration of the highest range winding and the reference winding: Connect the winding unit of the highest range to the preset first reference winding in reverse series. Through the induction of the primary winding and the secondary winding, use the ampere-turn meter of the secondary winding circuit to measure the difference in magnetomotive force between the winding unit of the highest range and the first reference winding to establish the equation relationship between the lowest range winding and the reference winding. Throughout the calibration process from S11 to S13, a fixed number of turns of the secondary winding is used as a unified reference. The measurement signals of the ampere-turn meter of the secondary winding circuit are collected, and the equations of the magnetomotive force difference between the windings are established in each calibration process. The equations are solved and the proportional error of each winding unit under different series and parallel combination states is corrected to complete the proportional calibration of the first-stage current comparator under the full range and full combination state. The two-stage calibration of the secondary comparator includes: The first level involves internal winding replacement and differential self-calibration: each subdivided winding unit to be calibrated in the second-level current comparator is selected sequentially, and current is passed in reverse to the second reference winding at the corresponding terminals. The difference in magnetomotive force between the subdivided winding unit to be calibrated and the second reference winding is measured by the ampere-turn meter in the secondary winding circuit. Based on the results of multiple replacement measurements, a set of equations reflecting the equivalent parameter deviation relationship between each subdivided winding unit to be calibrated and the second reference winding is established until the measurement of all subdivided winding units to be calibrated is completed, forming a solvable set of equations. The second level involves the overall self-calibration of the primary winding against the secondary winding for equal turns: The subdivided windings of the second-stage current comparator are connected in series to form a primary combined winding, ensuring that the total equivalent turns on the primary side are equal to the nominal turns of the secondary winding, thus establishing an equal turns condition. The primary combined winding with the equal turns condition is then connected in reverse parallel with the secondary winding. The difference in magnetomotive force between the primary combined winding and the secondary winding is measured using an ammeter in the secondary winding circuit to obtain the equal turns comparison result. The relative relationship between the windings obtained in the first level is combined with the equal turns comparison result to calculate the equivalent parameters of each subdivided winding unit and the secondary winding, completing the overall self-calibration.

[0032] Furthermore, the series-parallel calibration of the first-level comparator and the two-level calibration of the second-level comparator are both automatically executed by the control system through the proportional switching actuator, and a closed-loop calibration is formed through measurement, calculation, and parameter updating, without relying on external standard sources and manual operation; like Figure 2 As shown, the control system includes a host computer, a controller, and a proportional switching actuator. The host computer is used to store measurement data, establish and solve a system of equations, and generate correction coefficients. The controller is any one of a programmable logic controller (PLC), an industrial control computer, an embedded controller, or a microcontroller. The controller is communicatively connected to the host computer and the proportional switching actuator, respectively, and receives instructions from the host computer and controls the actuator to act according to a preset timing sequence. The proportional switching actuator is any one of a relay matrix, a magnetic latching relay array, or a solid-state relay array. The actuator is electrically connected to the winding of the two-stage current comparator to realize the switching of the winding's on / off state, combination, and connection mode.

[0033] Among them, such as Figure 3 As shown, the control process of the control system includes: S21. Obtain the target total current ratio, and generate a winding switching scheme based on the target total current ratio. The winding switching scheme includes the winding combination of the first-stage fixed ratio current comparator (denoted as T1), the winding combination of the second-stage variable ratio current comparator (denoted as T2), and the on / off action sequence of the proportional switching actuator connected to the two-stage current comparators. S22. Convert the winding switching scheme into control commands and send them to the controller; S23. The controller controls the proportional switching actuator to complete the winding connection of the two-stage current comparator and the connection mode configuration of the windings in series, parallel or reverse series according to the control command, so as to realize the proportional gear switching. S24. After the proportional gear switching is completed, the system enters a steady-state waiting stage. The output electrical signal of the current proportional standard device is collected by the measurement module and the signal stability is verified. Once the verification is successful, the programmable switching of the current ratio is completed.

[0034] The winding switching scheme is automatically generated by the host computer. The host computer has a built-in proportional gear mapping table and proportional decomposition logic. Based on the total number of turns ratio of the target current, it automatically decomposes the winding into the segmented turns ratio of the first-stage fixed proportional current comparator and the subdivided turns ratio of the second-stage variable proportional current comparator, and matches the corresponding winding combination and the on / off action timing of the proportional switching actuator.

[0035] After the first-stage current comparator completes full-range calibration, it automatically generates a proportional error correction table for each range and stores it in the control system for real-time correction in subsequent measurements.

[0036] After completing two-stage calibration, the second-stage current comparator automatically generates an equivalent parameter table for each subdivided winding unit and substitutes the equivalent parameters into the current ratio calculation model to achieve real-time correction of the ratio output.

[0037] The first-stage current comparator and the second-stage current comparator share the same reference power supply, the same ampere-turn magnetomotive force measurement circuit, and the same sampling circuit.

[0038] Among them, such as Figure 5 and Figure 6 As shown, in a specific embodiment, the two-stage cascaded current proportional standard device is a current proportional standard device consisting of a fixed-proportion decimal current comparator and a variable-proportion binary current comparator cascaded together. Then: The first-stage fixed-proportion current comparator is a decimal current comparator; the primary winding of the first-stage fixed-proportion current comparator includes at least one first reference winding and multiple decimal switching windings of different magnitudes. Each decimal switching winding of a magnitude includes 10 first winding units with the same number of turns. The number of turns of the first winding units in any two adjacent decimal switching windings of different magnitudes is changed according to the decimal magnitude. The number of turns of the first reference winding is the same as the number of turns of the decimal switching winding of the highest magnitude. The number of turns of the secondary winding of the first-stage fixed-proportion current comparator is determined by the fixed proportion. The second-stage variable proportional current comparator is a binary current comparator; the primary winding of the second-stage variable proportional current comparator includes at least one set of second reference windings and multiple binary switching windings, each binary switching winding including one second winding unit, and the number of turns of each second winding unit is 2. n Distribution, where n is a continuous natural number; the number of turns of the second reference winding is the same as the number of turns of the binary switching winding of the highest range; the number of turns of the secondary winding of the second-stage variable proportional current comparator is the same as the number of turns of the secondary winding of the first-stage fixed proportional current comparator, and the number of turns of the second winding unit of the lowest range is smaller than the number of turns of the secondary winding of the second-stage variable proportional current comparator.

[0039] This embodiment uses a cascaded two-stage current comparator (proportional multiplication) combined with a decimal and binary switching winding design to cover the DC current range from milliamperes to kiloamperes. The cascaded decimal and binary switching windings provide segmented ranges and several fixed ratios, while the binary switching winding provides subdivided ranges and variable ratios synthesized from arbitrary integer ratios, thus forming multi-level proportional outputs to meet wider range requirements (e.g., achieving range coverage from mA to kA).

[0040] Specifically, such as Figure 5 As shown, in an example of achieving range coverage from mA to kA, the fixed ratios include 1:1, 1:10, 1:100, and 1:1000; In the first-stage current comparator, the first reference winding is a group with 1 turn; the decimal switching winding array has 3 groups, and the number of turns of the first winding unit in each decimal switching winding is 1 turn, 10 turns and 100 turns respectively; the secondary winding is fixed at 1000 turns, so a fixed ratio of 1:10 to 1:1000 can be achieved.

[0041] like Figure 6 As shown, in the second-stage current comparator, the second reference winding is a group with 1 turn; n is a continuous natural number from 0 to 9; that is, the number of binary switching windings is 10, and the number of turns of the second winding unit is 1, 2, 4, 8, 16, 32, 64, 128, 256, and 512 turns respectively; the secondary winding is fixed at 1000 turns.

[0042] This specific example combines a first-stage decimal segmentation (1 / 10 / 100 turns) with a second-stage binary subdivision (2ⁿ distribution) to form multi-level proportional outputs ranging from 200mA:100mA to 1kA:100mA, covering the DC current range of 1mA to 1kA. The second stage adopts a binary design of "one switching winding containing one winding unit", which reduces the number of windings compared to the traditional multi-tap structure, reducing winding difficulty and cost. At the same time, it improves operating efficiency through programmable switching. Both stages are equipped with a one-turn reference winding as an internal calibration benchmark, which can complete the proportional parameter calibration without relying on an external standard source, ensuring the traceability of the proportional relationship, shortening the calibration cycle and reducing costs.

[0043] The series calibration of the primary winding of the first-stage current comparator involves calibrating each decimal switching winding of the primary winding using a series method. This is achieved through a winding switching switch, realizing the equivalent conversion between series and parallel windings, following the principle of "series calibration, parallel use". Specifically, it includes the following steps: Lowest range winding series calibration: After connecting each first winding unit in the decimal switching group of the lowest range in series, connect it in reverse parallel with the secondary winding with a fixed number of turns, and calibrate the proportional error of the combination by the difference comparison method. Intermediate range winding cascade calibration: Connect all the first winding units in the calibrated lowest range decimal switching winding in parallel (to achieve range extension), and then connect them in reverse series with all the first winding units after they are connected in series with the second lowest range decimal switching winding, perform differential comparison calibration, and establish the proportional relationship between the two. Stepwise recursive calibration until the highest range winding cascade calibration: sequentially connect the first winding unit of the currently calibrated decimal switching winding in parallel, and then connect it in reverse with the first winding unit of the decimal switching winding of the next higher range, until the decimal switching winding of the highest range is connected in reverse with the first reference winding, perform differential comparison calibration, and establish the proportional relationship between the two. Error Reading and Verification: Using a fixed number of turns as a reference throughout, the voltage signal across the load resistor is read to calculate and correct the proportional error of each winding unit under different series / parallel combinations, ensuring the accuracy of the proportional values ​​for each gear. For example... Figure 4 As shown, the self-calibration error of each turn ratio of T1 and T2 and the total proportional error of the two-stage cascade were tested. The results showed that the calibration error of each turn ratio was below ±0.2 ppm.

[0044] refer to Figure 5 As shown, taking a first-stage current comparator containing three sets of decimal switching windings as an example, the following steps are included: S11. Connect the 10×100 turns of the decimal switching winding in series and then connect them in reverse parallel with the secondary winding (1000 turns) to perform differential comparison calibration. S12. Then connect 10×100 turns in parallel, and then connect them in series with 10×10 turns in reverse to perform differential comparison calibration. S13. Connect 10×10 turns in parallel, and then connect them in series with 10×1 turns in reverse to perform differential comparison calibration; S14. Connect 10×1 turns in reverse series with the first reference winding (1 turn) and perform differential comparison calibration. During calibration, the secondary winding remains constant at 1000 turns, and the calibration error is obtained by reading the voltage across the load resistor. This method is used to calibrate the proportional values ​​of each decimal switching winding of the first-stage current comparator under different combination states.

[0045] The built-in self-calibration method of the second-stage current comparator includes two levels: The first level involves internal winding replacement and differential self-calibration: each subdivided winding unit to be calibrated in the second-level current comparator is selected sequentially, and current is passed in reverse to the second reference winding at the corresponding terminals. The difference in magnetomotive force between the subdivided winding unit to be calibrated and the second reference winding is measured by the ampere-turn meter in the secondary winding circuit. Based on the results of multiple replacement measurements, a set of equations reflecting the equivalent parameter deviation relationship between each subdivided winding unit to be calibrated and the second reference winding is established until the measurement of all subdivided winding units to be calibrated is completed, forming a solvable set of equations. like Figure 7 As shown, taking a binary switching winding with n=0, 1, 2…9 as an example, the binary switching winding… remember Let Wi be the reference winding, i = 1~10, and the second reference winding be denoted as W0 (1 turn). First, select the binary switching winding W1 to be calibrated, and apply current in opposite directions to the second reference winding W0 at their corresponding terminals to make their magnetomotive forces differ. Then, use fluxgate peak difference detector (or phase-sensitive detector) to detect the change in compensation current in the secondary winding (1000 turns). Through multiple substitution measurements, a set of equations describing the relative deviation of the equivalent number of turns (or equivalent magnetomotive force) of each winding can be established.

[0046] Then, select the binary switching winding W2 to be calibrated, connect it in series with the second reference winding W0 and the calibrated winding W1, and apply current in opposite directions to the corresponding terminals to create a difference in their magnetomotive forces. Measure the difference in magnetomotive force between the primary and secondary windings using an ampere-turn meter in the secondary winding circuit. Through multiple substitution measurements, a set of equations describing the relative deviation of the equivalent number of turns (or equivalent magnetomotive force) of each winding can be established.

[0047] Select the binary switching windings W3, W4...W10 to be calibrated in sequence, and repeat the above process until all binary windings are covered, forming a solvable set of equations.

[0048] The second level involves the overall self-calibration of the primary winding against the secondary winding for equal turns: The subdivided windings of the second-stage current comparator are connected in series to form a primary combined winding, ensuring that the total equivalent turns on the primary side are equal to the nominal turns of the secondary winding, thus establishing an equal turns condition. The primary combined winding with the equal turns condition is then connected in reverse parallel with the secondary winding. The difference in magnetomotive force between the primary combined winding and the secondary winding is measured using an ammeter in the secondary winding circuit to obtain the equal turns comparison result. The relative relationship between the windings obtained in the first level is combined with the equal turns comparison result to calculate the equivalent parameters of each subdivided winding unit and the secondary winding, completing the overall self-calibration.

[0049] like Figure 8 As shown, taking the binary switching winding with n=0, 1, 2…9 as an example, the binary switching winding… remember Let Wi be the number of turns, i = 1~10. Since the secondary winding has 1000 turns, to ensure a consistent comparison between the primary and secondary windings, the primary binary windings are connected in series according to the "binary expression of 1000" to achieve the equivalent number of turns of 1000. For example, connecting 512 turns, 256 turns, 128 turns, 64 turns, 32 turns, and 8 turns in series results in an equivalent number of turns of 1000. The primary and secondary windings are then connected in parallel in opposite directions, and the magnetomotive force difference between them is measured using an ampere-turn meter. The relative relationships of each winding obtained from internal self-calibration are combined with the overall 1000-turn comparison measurement to solve for the equivalent values ​​of each winding relative to the reference and the equivalent value of the secondary winding, thus achieving self-calibration.

[0050] The internal self-calibration mechanism reduces reliance on external calibration equipment, lowers calibration costs and cycles, avoids uncertainties introduced by manual operation, and improves measurement consistency during multi-level switching.

[0051] This calibration method does not rely on an additional high-current standard device in its structure. During implementation, it only requires the device's built-in current source to complete the calibration of the proportional parameters. Experimental verification shows that after self-calibration, the current proportional error of each range is less than ±0.2 ppm, and proportional drift can be detected and corrected in a timely manner, thereby effectively reducing the risk of proportional error accumulation during long-term operation.

[0052] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A current ratio standard self-calibration method without external standard source, characterized in that: It is applied to a current ratio standard device consisting of a first-stage fixed-proportion current comparator and a second-stage variable-proportion current comparator cascaded in proportion. The primary winding of the first-stage current comparator includes a first reference winding and multiple switching winding arrays for different ranges; each switching winding array contains several first winding units with the same number of turns, and the switching winding arrays for adjacent ranges increase or decrease according to a fixed ratio; the secondary winding of the first-stage current comparator is a winding with a fixed number of turns; the number of turns of the first reference winding is the same as the number of turns of the winding unit of the highest range switching winding array in the first-stage current comparator; The primary winding of the second-stage current comparator includes at least one set of second reference windings and multiple freely combinable subdivision winding units; the number of turns of each subdivision winding unit is distributed sequentially according to a preset weighting rule, and can form any target number of turns through the series combination of different winding units; the secondary winding of the second-stage current comparator is also a fixed number of turns winding, and its number of turns is the same as that of the secondary winding of the first-stage current comparator; the number of turns of the second reference winding is the same as the number of turns of the highest range subdivision winding unit in the second-stage current comparator; and the number of turns of the lowest range subdivision winding unit in the second-stage current comparator is less than the number of turns of the secondary winding of the second-stage current comparator. The method includes two-stage calibration: a first-stage current comparator calibration and a second-stage current comparator calibration. The order of the first-stage current comparator calibration and the second-stage current comparator calibration is not limited. The first-stage current comparator is calibrated using a series-parallel method, specifically including: S11. Lowest range winding series calibration: Connect all winding units corresponding to the lowest range setting in series to form a series combined winding; connect this series combined winding in reverse parallel with a secondary winding with a fixed number of turns, and use an ampere-turn meter in the secondary winding circuit to measure the difference in magnetomotive force between the series combined winding and the secondary winding to establish an equation relationship. S12. Intermediate range winding stepwise calibration: Switch all winding units of the calibrated previous range winding to a parallel state to form a previous parallel winding; connect the current next range winding to be calibrated in series to form a next series winding; then connect the previous parallel winding and the next series winding in reverse series to close the circuit, and use the ampere-turn meter in the secondary winding circuit to measure the difference in magnetomotive force between the previous parallel winding and the next series winding to establish the proportional relationship between the two range windings. Repeat the above recursive process in order from low range to high range to complete the calibration of all intermediate range windings in sequence. S13. Calibration of the highest range winding and the reference winding: Connect the winding unit of the highest range to the preset first reference winding in reverse series. Through the induction of the primary winding and the secondary winding, use the ampere-turn meter of the secondary winding circuit to measure the difference in magnetomotive force between the winding unit of the highest range and the first reference winding to establish the equation relationship between the lowest range winding and the reference winding. Throughout the calibration process from S11 to S13, a fixed number of turns of the secondary winding is used as a unified reference. The measurement signals of the ampere-turn meter of the secondary winding circuit are collected, and the equations of the magnetomotive force difference between the windings are established in each calibration process. The equations are solved and the proportional error of each winding unit under different series and parallel combination states is corrected to complete the proportional calibration of the first-stage current comparator under the full range and full combination state. The two-stage calibration of the secondary comparator includes: The first level involves internal winding replacement and differential self-calibration: each subdivided winding unit to be calibrated in the second-level current comparator is selected sequentially, and current is passed in reverse to the second reference winding at the corresponding terminals. The difference in magnetomotive force between the subdivided winding unit to be calibrated and the second reference winding is measured by the ampere-turn meter in the secondary winding circuit. Based on the results of multiple replacement measurements, a set of equations reflecting the equivalent parameter deviation relationship between each subdivided winding unit to be calibrated and the second reference winding is established until the measurement of all subdivided winding units to be calibrated is completed, forming a solvable set of equations. The second level involves the overall self-calibration of the primary winding against the secondary winding for equal turns: The subdivided windings of the second-stage current comparator are connected in series to form a primary combined winding, ensuring that the total equivalent turns on the primary side are equal to the nominal turns of the secondary winding, thus establishing an equal turns condition. The primary combined winding with the equal turns condition is then connected in reverse parallel with the secondary winding. The difference in magnetomotive force between the primary combined winding and the secondary winding is measured using an ammeter in the secondary winding circuit to obtain the equal turns comparison result. The relative relationship between the windings obtained in the first level is combined with the equal turns comparison result to calculate the equivalent parameters of each subdivided winding unit and the secondary winding, completing the overall self-calibration.

2. A current ratio standard self-calibration method without external standard source as claimed in claim 1 characterized by: The series-parallel calibration of the first-level comparator and the two-level calibration of the second-level comparator are both automatically executed by the control system through the proportional switching actuator, and a closed-loop calibration is formed through measurement, calculation and parameter updating. The control system includes a host computer, a controller, and a proportional switching actuator. The host computer is used to store measurement data, establish and solve a set of equations, and generate correction coefficients. The controller is any one of a programmable logic controller, an industrial control computer, an embedded controller, or a microcontroller. The controller is communicatively connected to the host computer and the proportional switching actuator, respectively, and receives instructions from the host computer and controls the actuator to act according to a preset timing sequence. The proportional switching actuator is any one of a relay matrix, a magnetic latching relay array, or a solid-state relay array. The actuator is electrically connected to the winding of the two-stage current comparator to realize the switching of the winding's on / off state, combination, and connection mode.

3. A current ratio standard self-calibration method without external standard source as claimed in claim 1 characterized by: The first-stage fixed-proportion current comparator is a decimal current comparator; the primary winding of the first-stage fixed-proportion current comparator includes at least one first reference winding and multiple decimal switching windings of different magnitudes. Each decimal switching winding of a magnitude includes 10 first winding units with the same number of turns. The number of turns of the first winding units in any two adjacent decimal switching windings of different magnitudes is changed according to the decimal magnitude. The number of turns of the first reference winding is the same as the number of turns of the decimal switching winding of the highest magnitude. The number of turns of the secondary winding of the first-stage fixed-proportion current comparator is determined by the fixed proportion. The second-stage variable proportional current comparator is a binary current comparator; The primary winding of the second-stage variable proportional current comparator includes at least one set of second reference windings and multiple binary switching windings. Each binary switching winding includes one second winding unit, and the number of turns of each second winding unit is 2. n Distribution, where n is a continuous natural number; the number of turns of the second reference winding is the same as the number of turns of the binary switching winding of the highest range; the number of turns of the secondary winding of the second-stage variable proportional current comparator is the same as the number of turns of the secondary winding of the first-stage fixed proportional current comparator, and the number of turns of the second winding unit of the lowest range is smaller than the number of turns of the secondary winding of the second-stage variable proportional current comparator.

4. The self-calibration method for a current proportional standard without an external standard source as described in claim 1, characterized in that: The fixed ratios include 1:1, 1:10, 1:100, and 1:1000; In the first-stage current comparator, the first reference winding is a group with 1 turn; the number of decimal switching windings is 3, and the number of turns of the first winding unit in each decimal switching winding is 1 turn, 10 turns and 100 turns respectively. In the second-stage current comparator, the second reference winding is a group with 1 turn; n is a continuous natural number from 0 to 9; that is, the number of binary switching windings is 10, and the number of turns of the second winding unit is 1, 2, 4, 8, 16, 32, 64, 128, 256, and 512 turns respectively. The number of turns in the secondary winding of the first-stage current comparator and the secondary winding of the second-stage current comparator are both 1000 turns.

5. The self-calibration method for a current proportional standard without an external standard source as described in claim 1, characterized in that: After the first-stage current comparator completes full-range calibration, it automatically generates a proportional error correction table for each range and stores it in the control system for real-time correction in subsequent measurements.

6. The self-calibration method for a current proportional standard without an external standard source as described in claim 1, characterized in that: After completing two-stage calibration, the second-stage current comparator automatically generates an equivalent parameter table for each subdivided winding unit and substitutes the equivalent parameters into the current ratio calculation model to achieve real-time correction of the ratio output.

7. A current ratio standard self-calibration method without external standard source as claimed in claim 1 characterized by: The first-stage current comparator and the second-stage current comparator share the same reference power supply, the same ampere-turn magnetomotive force measurement circuit, and the same sampling circuit.

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