A large current sensor calibration system based on direct current proportion standard

Abstract

This invention belongs to the field of electrical measurement instrument calibration technology and discloses a high-current sensor calibration system based on a DC current proportional standard. The system includes an optical error measurement unit, an electromagnetic proportional standard unit, a control and calculation unit, and a sensor interface unit. The optical sensing component and the secondary compensation winding are wound on the same magnetic core and detect the synthesized magnetomotive force to output an optical signal. The control and calculation unit includes a signal processing module, a mode discrimination module, a closed-loop control module, and a data fusion module. In magnetomotive force balance mode, the measurement coefficients of the optical sensing component are calibrated using a standard proportional value. In difference correction mode, the standard proportional value is corrected by addition or multiplication using the synthesized magnetomotive force deviation. The sensor interface unit acquires the output signal of the sensor being calibrated and compares it with the corrected standard proportional value to calculate the measurement error. This invention achieves high-precision calibration of high-current sensors across the entire measurement range, possesses internal self-traceability, and exhibits good environmental adaptability.

Description

Technical Field

[0001] This invention relates to the field of electrical measurement instrument calibration technology, specifically a high-current sensor calibration system based on a DC current ratio standard. Background Technology

[0002] High-current DC sensors play a crucial measurement role in fields such as metal smelting, chlor-alkali chemical industry, electroplating, ship propulsion, high-speed rail locomotives, and high-voltage DC power transmission. Their calibration accuracy directly affects product quality, production safety, and energy efficiency. Currently, calibration systems based on DC current proportional standards are the mainstream technology in this field. Among them, the DC current comparator (DCC), as an electromagnetic proportional standard, has high proportional accuracy, reaching the order of one part per million, in the range of small and conventional currents. Meanwhile, fiber optic current sensors (FOCS) have received widespread attention in the field of ultra-high current measurement due to their advantages such as good insulation performance, strong resistance to electromagnetic interference, and no magnetic saturation problem. In existing calibration systems, self-calibration methods such as the equal ampere-turn method, reference winding method, additive calibration, and multiplicative calibration are already in use. Temperature compensation and bus structure optimization technologies have also been introduced as auxiliary means. These technologies together constitute the basic technical framework of existing high-current sensor calibration systems.

[0003] However, the aforementioned existing technologies still have the following shortcomings. First, in the high-current range, the permeability of electromagnetic proportional standards drops sharply due to core saturation, significantly deteriorating the accuracy of magnetomotive force balance control. This results in calibration accuracy under high current conditions being far lower than under low current conditions, and a single operating mode cannot maintain high-precision calibration across the entire range. Second, existing self-calibration methods, such as the equal ampere-turn method and the reference winding method, require a large number of proportional terminals and involve numerous measurement steps, causing the calibration system to rely on external higher-level standards for value transfer, resulting in a long traceability chain and high operating costs. Third, the strong leakage flux and temperature changes generated by the busbar under high-current conditions significantly interfere with calibration accuracy. Existing systems lack a collaborative mechanism between optical sensing components and temperature compensation, and there are no effective internal self-traceability methods, making it difficult to guarantee the stability and reliability of long-term calibration results. Summary of the Invention

[0004] This invention provides a high-current sensor calibration system based on a DC current proportional standard, comprising an optical error measurement unit, an electromagnetic proportional standard unit, a control and calculation unit, and a sensor-under-calibration interface unit. The optical sensing component and the secondary compensation winding are wound on the same magnetic core and detect the synthetic magnetomotive force. The electromagnetic proportional standard unit outputs a standard proportional value. The control and calculation unit includes signal processing, mode discrimination, closed-loop control, and data fusion modules. In magnetomotive force balance mode, the measurement coefficients of the optical sensing component are calibrated using the standard proportional value. In difference correction mode, the standard proportional value is corrected using the synthetic magnetomotive force deviation. The measurement error is calculated after acquiring the output signal of the sensor under calibration through the sensor-under-calibration interface unit. This invention achieves high-precision adaptive calibration across the entire measurement range and possesses internal self-traceability capabilities.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a high-current sensor calibration system based on a DC current ratio standard, comprising: an optical error measurement unit and an optical sensing component, wherein the optical sensing component and the secondary compensation winding are wound on the same magnetic core, and the optical sensing component detects the combined magnetomotive force generated by the primary side DC current and the secondary side compensation current in the magnetic core and outputs an optical signal. An electromagnetic proportional standard unit includes the magnetic core, a primary winding and a secondary winding wound on the magnetic core, and a current injection module. The current injection module injects a compensation current into the secondary winding. Under the magnetomotive force balance state, the electromagnetic proportional standard unit outputs a standard proportional value according to the turns ratio of the primary winding to the secondary winding and the compensation current. The control and computing unit includes a signal processing module, a pattern discrimination module, a closed-loop control module, and a data fusion module; The signal processing module converts the optical signal into an electrical signal corresponding to the synthesized magnetomotive force; the mode discrimination module determines the current working mode as either magnetomotive force balance mode or measurement difference correction mode based on the electrical signal. In the magnetic potential balance mode, the closed-loop control module drives the current injection module to adjust the compensation current until the synthetic magnetic potential is zero according to the synthetic magnetic potential. In the difference correction mode, the compensation current is kept constant and the measured value of the synthetic magnetic potential is obtained as the deviation. The data fusion module calibrates the measurement coefficient of the optical sensing component using the standard ratio value when the magnetic potential balance mode is in the magnetic core and the magnetic core is in the unsaturated working region. In the difference correction mode, the standard ratio value is corrected by addition or multiplication using the deviation amount to obtain the corrected standard ratio value. The sensor interface unit is connected to the sensor being calibrated, acquires the output signal of the sensor being calibrated, compares it with the corrected standard ratio value, and calculates the measurement error.

[0006] Preferably, the optical sensing component includes an optical fiber sensing element based on the Faraday magneto-optical effect.

[0007] Preferably, the mode discrimination module determines the magnetomotive force balance mode based on the signal-to-noise ratio of the electrical signal, and determines the differential correction mode based on the rate of change of the electrical signal with the primary current.

[0008] Preferably, the magnetic potential balance mode and the differential measurement correction mode share the same hardware architecture, and only the control parameters of the closed-loop control module are changed when switching between the two modes.

[0009] Preferably, the data fusion module performs a self-test procedure during system startup or maintenance, and performs self-monitoring by cyclically calibrating the optical sensing component in the magnetic potential balance mode and when the magnetic core is in the unsaturated operating region, and correcting the proportional deviation of the electromagnetic proportional standard unit in the difference correction mode.

[0010] Preferably, it also includes a temperature compensation module, which monitors the core temperature and the ambient temperature to compensate for the temperature drift of the optical sensing component and the temperature coefficient of the magnetic permeability of the core.

[0011] Preferably, the primary winding includes a plurality of sub-windings distributed along the circumference of the magnetic core, and the plurality of sub-windings constitute a distributed homogenized bus structure.

[0012] Preferably, the control and calculation unit further includes an error calculation module, which calculates the ratio difference at each calibration point by comparing the corrected standard ratio value with the output value of the calibrated sensor.

[0013] Preferably, the magnetic core is a toroidal iron core.

[0014] Preferably, the optical error measurement unit, the electromagnetic proportional standard unit, the control and calculation unit, and the interface unit of the sensor being calibrated are integrated into the same calibration platform to form a closed-loop calibration system.

[0015] Compared with the prior art, the present invention provides a high-current sensor calibration system based on a DC current ratio standard, which has the following advantages: 1. This invention achieves deep integration of optical sensing components and electromagnetic proportional standard units. In the magnetic potential balance mode, the measurement coefficients of the optical sensing components are calibrated with standard proportional values. In the difference correction mode, the proportional deviation of the electromagnetic proportional standard unit is corrected with the synthetic magnetic potential deviation measured by the optical sensing components. This realizes the complementarity and synergy of the two working modes, overcomes the defect of accuracy degradation under high current in traditional single mode, and maintains high-precision calibration across the entire range.

[0016] 2. This invention calibrates the optical sensing components in the low current range and corrects the electromagnetic proportional standard unit in the high current range through a data fusion module, achieving internal self-traceability of the system. It can ensure the long-term reliability of calibration results without relying on external higher-level standards, reducing the cost of using the calibration system and the difficulty of traceability.

[0017] 3. This invention compensates for the temperature drift of the optical sensing components and the temperature coefficient of magnetic permeability of the magnetic core through a temperature compensation module, and reduces leakage magnetic interference by combining a distributed homogenized bus structure, which significantly improves the calibration stability and environmental adaptability of the system under varying temperature and strong interference conditions. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the system structure of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Purpose of implementation: The purpose of this embodiment is to verify the feasibility of calibrating the measurement coefficients of optical sensing components in the magnetic potential balance mode, and to evaluate the calibration accuracy of the system in the low current and normal current range (the non-saturated operating region of the magnetic core).

[0021] Implementation System: This embodiment employs the following system configuration. The magnetic core is a high-permeability toroidal iron core made of 1J85 permalloy, with an initial permeability of not less than 80,000. The core has an inner diameter of 300 mm, an outer diameter of 500 mm, and a height of 80 mm. The primary winding uses a through-hole structure with one turn; the secondary winding has one thousand turns. The optical sensing component uses a full-fiber current sensor based on the Faraday magneto-optical effect. Its sensing fiber is uniformly arranged around the magnetic core and wound together with the secondary compensation winding on the same magnetic core. The object to be calibrated is a DC Hall current sensor with a rated current of one thousand amperes and an accuracy class of zero.02. This sensor is connected to the system through the sensor interface unit. A high-current DC steady source is used to apply the measured current to the primary winding.

[0022] Implementation method: After the system is started, a high-current DC regulated source applies the measured current to the primary winding, gradually increasing it from fifty amperes to one thousand amperes. When the magnetic core is in the unsaturated operating region, i.e., when the primary magnetomotive force does not exceed 80% of the product of the core's saturation magnetic flux density and its effective cross-sectional area, the mode discrimination module determines the current operating mode based on the signal-to-noise ratio (SNR) of the electrical signal output by the signal processing module. In this embodiment, the measured SNR is not less than sixty decibels and is higher than the preset threshold of forty decibels; therefore, the mode discrimination module determines the current operating mode to be the magnetomotive force balance mode.

[0023] The closed-loop control module drives the current injection module to inject compensation current into the secondary winding based on the synthesized magnetomotive force signal until the synthesized magnetomotive force, i.e., the difference between the primary and secondary magnetomotive forces, approaches zero. At this point, the electromagnetic proportional standard unit outputs a standard proportional value based on the turns ratio of the primary to secondary windings (1:1000) and the compensation current. This standard proportional value is equal to the compensation current multiplied by 1000.

[0024] In this magnetic potential balance mode, the data fusion module calibrates the measurement coefficients of the optical sensing component using a standard proportional value. The calibration method involves recording the correspondence between the amplitude of the optical signal output by the optical sensing component and the standard proportional value at multiple calibration points, and then using the least squares method to fit the measurement coefficients, i.e., the standard proportional value divided by the optical signal amplitude. In this embodiment, the calibration yields a measurement coefficient of 1.0023 for the optical sensing component, and the linear fitting determination coefficient is not less than 0.9999.

[0025] The interface unit of the sensor under calibration synchronously acquires the output voltage signal of the Hall current sensor under calibration. The data fusion module compares the standard ratio value with the output value of the sensor under calibration after converting it into a current value through the sensor's nominal transformation ratio. The error calculation module calculates the ratio difference at each calibration point. The ratio difference is the difference between the converted current value of the sensor under calibration and the standard ratio value, divided by the standard ratio value and then multiplied by 100%.

[0026] During calibration, the temperature compensation module simultaneously monitors the core temperature and ambient temperature, providing real-time compensation for temperature drift of the optical sensing component and the temperature coefficient of magnetic core permeability. In this embodiment, the measured temperature fluctuation range is 20 to 22 degrees Celsius, the temperature coefficient of the optical sensing component is approximately -2.3 x 10^-4 per degree Celsius, and the temperature coefficient of magnetic core permeability is approximately -3.5 x 10^-4 per degree Celsius.

[0027] Implementation results: Calibration results show that the maximum specific error of the Hall current sensor in the range of 50 amperes to 1000 amperes is positive 0.018%, meeting the accuracy requirement of level 0.02. The calibration uncertainty of the measurement coefficient of the optical sensing component is better than 2 x 10^-6. This embodiment verifies that the present invention can perform high-precision calibration of the optical sensing component using the standard proportional value output by the electromagnetic proportional standard unit in the magnetic potential balance mode, providing a foundation for accurate measurement of deviation in the difference correction mode.

[0028] Example 2 Purpose of implementation: The purpose of this embodiment is to verify the feasibility of correcting the proportional deviation of the electromagnetic proportional standard unit by using the synthetic magnetomotive force deviation measured by the optical sensing component in the differential correction mode, and to evaluate the calibration accuracy of the system in the high current range (core saturation operating region).

[0029] Implementation System: This embodiment uses the same system configuration as Embodiment 1. The specifications of the magnetic core, primary winding, secondary winding, and optical sensing components are consistent with those in Embodiment 1, wherein the primary winding has one turn and the secondary winding has five thousand turns. The object to be calibrated is a shunt with a rated current of five thousand amperes and an accuracy class of 0.05, which is connected to the system through the sensor interface unit to be calibrated.

[0030] Implementation method: A high-current DC steady current source applies the measured current to the primary winding, gradually increasing it from 500 amperes to 5,000 amperes. When the primary current increases to over 3,000 amperes, the magnetic core gradually enters the saturation operating region, i.e., the primary magnetomotive force exceeds 80% of the product of the core's saturation magnetic flux density and its effective cross-sectional area. The mode discrimination module detects that the rate of change of the electrical signal with the primary current abruptly changes from 1.02 millivolts per ampere in the linear region to 0.31 millivolts per ampere in the saturation region. This rate of change exceeds a preset threshold, which is 50% of the slope of the linear region. The mode discrimination module automatically determines that the current operating mode is the difference correction mode.

[0031] The closed-loop control module maintains the current secondary compensation current unchanged. In this embodiment, when the primary current is 4,000 amperes, the compensation current is approximately 0.6 amperes, corresponding to a theoretical standard proportional value equal to the compensation current multiplied by 5,000, i.e., 3,000 amperes. The optical sensing component detects the synthetic magnetomotive force in the magnetic core in real time, i.e., the primary magnetomotive force minus the secondary magnetomotive force. The output optical signal is converted into an electrical signal by the signal processing module, and the data fusion module obtains the measured value of the synthetic magnetomotive force as the deviation.

[0032] The data fusion module uses this deviation to additively correct the standard ratio value. The corrected standard ratio value is equal to the theoretical standard ratio value plus the product of the deviation and the measurement coefficient of the optical sensing component, where the measurement coefficient is the value calibrated in Example 1. In this example, when the primary current is 4,000 amperes, the theoretical standard ratio value is 3,000 amperes, the deviation of the synthetic magnetomotive force measured by the optical sensing component is 998.7 amperes, and the corrected standard ratio value is approximately 4,001.0 amperes.

[0033] The interface unit of the sensor under calibration synchronously acquires the output voltage signal of the shunt. In this embodiment, the measured output voltage is 60.02 millivolts, corresponding to a current value of 4001.3 amperes. The error calculation module compares the corrected standard ratio value of 4001.0 amperes with the output value of 4001.3 amperes of the sensor under calibration, and then calculates the ratio difference at the calibration point.

[0034] Implementation results: Full-range calibration results show that the maximum ratio difference of the shunt in the range of 500 amperes to 5000 amperes is positive 0.038%, meeting the accuracy requirement of 0.05 class. At the 4000 ampere calibration point, the deviation between the corrected standard ratio value of 4001.0 amperes and the actual applied primary current of 4000 amperes is only positive 0.025%, while the deviation between the uncorrected theoretical standard ratio value of 3000 amperes and the actual value reaches 25%. This embodiment verifies that the present invention can still achieve high-precision calibration through the difference correction mode under the condition of magnetic core saturation, overcoming the defect of the traditional electromagnetic ratio standard that causes a sharp drop in accuracy due to iron core saturation under high current.

[0035] Example 3 Purpose of implementation: The purpose of this embodiment is to verify the feasibility of the data fusion module of the present invention executing a self-test procedure during system startup or maintenance and achieving long-term stability self-monitoring of the system through cyclic mutual calibration.

[0036] Implementation System: This embodiment uses the same system configuration as Embodiment 1. The specifications and parameters of the magnetic core, primary winding, secondary winding, optical sensing component, current injection module, and control and computing unit are consistent with those in Embodiment 1. The object to be calibrated is a DC current transformer with a rated current of 2000 amperes and an accuracy class of 0.01, which is connected to the system through the sensor interface unit. The data fusion module internally stores historical calibration parameters, including the measurement coefficients of the optical sensing component calibrated during the last self-test and correction records for each calibration point.

[0037] Implementation method: After the system starts up, the data fusion module automatically runs an internal self-test program. This self-test program consists of three parts.

[0038] The first part calibrates the optical sensing component in the low-current range. When the primary current is 200 amperes, i.e., the magnetic core is in the unsaturated operating region, the system operates in magnetomotive force balance mode. The closed-loop control module adjusts the compensation current to bring the synthesized magnetomotive force close to zero. The electromagnetic proportional standard unit outputs a standard proportional value; in this embodiment, the measured standard proportional value is 200.01 amperes. The data fusion module calibrates the current measurement coefficient of the optical sensing component using this standard proportional value, i.e., the standard proportional value divided by the amplitude of the optical signal output by the optical sensing component. The data fusion module compares the current calibration value with historical calibration values. In this embodiment, the deviation is positive 0.012%, which is less than the preset alarm threshold of ±0.05%, and the self-test procedure continues.

[0039] The second part is the correction of the electromagnetic proportional standard unit in the high current range. When the primary current is 1,800 amperes, that is, when the magnetic core enters the saturation operating region, the system switches to the difference correction mode. The proportional deviation of the electromagnetic proportional standard unit is corrected by the synthetic magnetomotive force deviation measured by the optical sensing components calibrated in the first part, so as to obtain the corrected standard proportional value.

[0040] The third part is cross-validation. With a current of 1000 amperes, i.e., when the magnetic core is in the critical saturation region, the standard proportional value in the magnetomotive force balance mode and the corrected standard proportional value in the measurement correction mode are recorded respectively. The deviation between the two is calculated, which is the absolute value of the difference divided by the standard proportional value in the magnetomotive force balance mode and then multiplied by 100%. In this embodiment, the deviation is 4.7 x 10⁻⁶, which is less than the preset validation threshold of 1 x 10⁻⁵, thus the self-test passes.

[0041] Implementation results: The entire self-test procedure takes approximately twelve minutes and requires no external standard. This embodiment verifies the cyclic cross-calibration mechanism of calibrating the optical sensing components in the low-current range and correcting the electromagnetic proportional standard unit in the high-current range. This allows the system to achieve internal self-traceability without relying on external higher-level standards. The self-test procedure effectively monitors parameter drift during long-term system operation. When calibration deviation or cross-validation deviation exceeds a preset threshold, the system issues an alarm indicating a maintenance requirement, thus ensuring the long-term reliability of calibration results.

[0042] Example 4 Purpose of implementation: The purpose of this embodiment is to verify the implementation effect of the distributed homogenized bus structure and temperature compensation module of the present invention under high current and variable temperature conditions, and to evaluate the effect of the combined application of the two on improving the system calibration accuracy and long-term stability.

[0043] Implementation System: This embodiment employs the following system configuration. The magnetic core is a high-permeability toroidal iron core. The primary winding adopts a distributed homogenized bus structure: the primary bus is divided into eight sub-windings, evenly distributed along the circumference of the magnetic core, with each sub-winding independently passing through a window in the magnetic core before merging. The conductor cross-sectional area of ​​each sub-winding is 400 square millimeters, arranged every 45 degrees on the circumference of the magnetic core. The eight sub-windings undergo length matching before merging, with the length difference between each sub-winding not exceeding ±5 millimeters to ensure consistent impedance in each branch. The secondary winding has 8,000 turns. The specifications of the optical sensing component are consistent with those in Embodiment 1. The temperature compensation module includes three platinum resistance temperature sensors, respectively mounted on the outer surface of the magnetic core, the optical sensing component's encapsulation shell, and the calibration system's environmental cavity. The temperature sampling rate is 10 Hz, and the resolution is 0.01 degrees Celsius. The object to be calibrated is a zero-flux current sensor with a rated current of 10,000 amperes and an accuracy class of 0.02, which is connected to the system through the sensor interface unit.

[0044] Implementation method: The high-current DC regulated power source outputs 10,000 amperes of current, which is evenly distributed among eight sub-windings, with each sub-winding carrying approximately 1,250 amperes. The temperature compensation module collects temperature data from each measuring point in real time.

[0045] The temperature compensation module corrects the measurement results according to the following compensation model. For temperature drift compensation of the optical sensing component, the compensation amount equals the first-order coefficient multiplied by the temperature difference plus the second-order coefficient multiplied by the square of the temperature difference. The first-order coefficient is -2.3 x 10⁻⁴ per degree Celsius, the second-order coefficient is 4.1 x 10⁻⁶ per square degree Celsius, and the temperature difference is the difference between the measured temperature and the reference temperature (20 degrees Celsius). For core permeability temperature coefficient compensation, the compensation amount equals the core material temperature coefficient multiplied by the temperature difference. The core material temperature coefficient is -3.5 x 10⁻⁴ per degree Celsius.

[0046] The data fusion module corrects the measurement coefficients of the optical sensing components and the standard ratio values ​​of the electromagnetic proportional standard unit in real time based on the compensation amount output by the temperature compensation module.

[0047] Implementation results: During the ambient temperature change from 15 degrees Celsius to 35 degrees Celsius, without temperature compensation, the calibration uncertainty of the system across the entire range deteriorated from 2.3 x 10⁻⁶ to 8.7 x 10⁻⁶. After enabling temperature compensation, the calibration uncertainty stabilized within the range of 2.8 x 10⁻⁶ to 3.5 x 10⁻⁶. The distributed homogenized bus structure ensures that the current distribution deviation between each sub-winding does not exceed ±0.03%, effectively reducing the impact of leakage magnetic interference generated by the high-current bus on the calibrated sensor and magnetic core. This embodiment verifies the combined implementation scheme of the distributed homogenized bus structure and the temperature compensation module, which can significantly improve the calibration accuracy and long-term stability of the system under high-current and variable-temperature conditions.

[0048] Comparative Example 1 Purpose of implementation: The purpose of this comparative example is to verify, by comparing it with the differential correction mode of this invention, the problem of insufficient calibration accuracy of the traditional single magnetomotive force balance mode in the high current range (core saturation operating region).

[0049] Implementation System: This comparative example uses the same hardware platform as Example 2, including the same magnetic core, primary winding (one turn), secondary winding (five thousand turns), optical sensing components, current injection module, and sensor interface unit. The object to be calibrated is the same as in Example 2, a shunt with a rated current of five thousand amperes and an accuracy class of 0.05. The difference between this comparative example and Example 2 is that the difference correction mode function is disabled, and the system only runs the traditional magnetomotive force balance mode for calibration.

[0050] Implementation method: A high-current DC steady-state source applies the measured current to the primary winding, gradually increasing it from 500 amperes to 5,000 amperes. The system always operates in magnetomotive force balance mode, with the closed-loop control module continuously adjusting the compensation current to try to bring the synthesized magnetomotive force (MTF) towards zero. When the primary current is below 3,000 amperes, the magnetic core is in the unsaturated operating region, and the closed-loop control can effectively maintain the MMF balance. When the primary current exceeds 3,000 amperes, the magnetic core enters the saturation region, and the permeability drops sharply. Although the closed-loop control module continuously adjusts the compensation current, the control accuracy of the MMF balance deteriorates significantly, and the synthesized MMF cannot be effectively brought to zero. When the primary current is 4,000 amperes, the measured synthesized MMF is approximately 1,010 amperes (equivalent deviation), and the deviation between the calculated standard proportional value and the actual applied primary current is approximately positive 0.09%. When the primary current is 5,000 amperes, the deviation further expands to approximately positive 0.15%.

[0051] Implementation results: In this comparative example, at the 5000 ampere calibration point, the difference between the standard ratio value obtained from the single magnetomotive force balance mode and the output value of the calibrated sensor reached 0.152%, far exceeding the maximum permissible error of the 0.05-stage shunt (±0.05%), rendering the calibration result unusable. At the 3000 ampere calibration point, the difference was 0.035%, and at the 4000 ampere calibration point, it was 0.087%. This comparative example demonstrates that the traditional single magnetomotive force balance mode suffers a sharp drop in accuracy under high current due to core saturation, failing to meet the calibration requirements of high-accuracy, high-current sensors. This invention, by introducing a difference correction mode, uses the synthetic magnetomotive force deviation measured by the optical sensing component in the core saturation region to correct the standard ratio value in real time. The maximum difference across the entire range is only 0.038%, fundamentally solving this technical problem.

[0052] Comparative Example 2 Purpose of implementation: The purpose of this comparative example is to verify the limitation of calibration accuracy when using an optical fiber current sensor as an independent external reference standard by comparing it with the deep integration scheme of the optical sensing component and electromagnetic proportional standard unit of the present invention.

[0053] Implementation System: This comparative example uses the same hardware platform as Example 1, including the same fiber optic sensing components, the sensor interface unit to be calibrated, and the object to be calibrated (a DC Hall current sensor with a rated current of 1000 amperes and an accuracy class of 0.02). The difference between this comparative example and Example 1 is that: the sensing fiber of the fiber optic current sensor is directly wound around the primary bus and installed independently, rather than being wound together with the secondary compensation winding on the same magnetic core; the electromagnetic proportional standard unit does not participate in the calibration process, and its calibration function is turned off; the fiber optic current sensor is used as an independent external reference standard, and its measured value is directly used as the reference standard value.

[0054] Implementation method: A high-current DC regulated power source applies the measured current to the primary winding, gradually increasing it from 100 amperes to 1000 amperes. A fiber optic current sensor independently measures the primary current value. This measured value is used as a reference standard and compared with the output value of the Hall current sensor being calibrated. The difference is calculated: the difference between the converted current value of the calibrated sensor and the measured value of the fiber optic sensor, divided by the measured value of the fiber optic sensor, and then multiplied by 100%. Calibration is performed under identical environmental conditions: an ambient temperature of 20 degrees Celsius ± 1 degree Celsius and a humidity of 50% ± 5%.

[0055] Implementation results: In this comparative example, the difference is 0.083% positive at the 100 ampere calibration point, 0.071% positive at the 500 ampere calibration point, and 0.065% positive at the 1000 ampere calibration point. The deviation between the single current value measured independently by the fiber optic current sensor and the true value mainly comes from two aspects: first, the fiber optic sensing element is not traceable and its measurement coefficient has a systematic deviation of about 0.05% to 0.08%; second, the fiber optic sensing element is sensitive to ambient temperature, and even under the same environmental conditions, there is still a residual temperature drift of about 0.02% to 0.03%. However, in Embodiment 1 of this invention, after the fiber optic sensing component is calibrated by the electromagnetic proportional standard unit in the low current range, its equivalent measurement uncertainty is improved from about five times ten to the power of -4 when used independently to better than two times ten to the power of -6, and the calibration accuracy is improved by more than two orders of magnitude. This comparative example demonstrates that when using a fiber optic current sensor as an independent external reference standard, its calibration accuracy is limited by the sensor's own accuracy class, typically ranging from 0.1 to 0.5, due to the lack of effective traceable calibration methods. This fails to meet the calibration requirements of high-accuracy, high-current sensors, i.e., 0.02 and above. This invention achieves a deep integration and complementary performance of two principles by internalizing the optical sensing component as an error detection component within the system and calibrating it using an electromagnetic proportional standard unit in the low-current range.

[0056] This invention can be widely applied in metrology and testing institutions as a standard for high-current DC operation; for high-current sensor manufacturers for factory verification; in the metallurgical electrolysis field for monitoring and calibrating currents in the tens of thousands of amperes range; in power systems for calibrating current transformers in DC transmission converter stations; in the rail transit field for calibrating locomotive traction current sensors; and in the electric vehicle field for calibrating battery pack charging and discharging current sensors. The system achieves calibration uncertainty better than 1 x 10^-6 across its entire measurement range and maintains stable operation even under harsh conditions such as strong electromagnetic interference and high-current heating.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A calibration system for a high-current sensor based on a DC current ratio standard, characterized in that, include: An optical error measurement unit and an optical sensing component are provided. The optical sensing component and the secondary compensation winding are wound on the same magnetic core. The optical sensing component detects the combined magnetomotive force generated by the primary side DC current and the secondary side compensation current in the magnetic core and outputs an optical signal. An electromagnetic proportional standard unit includes the magnetic core, a primary winding and a secondary winding wound on the magnetic core, and a current injection module. The current injection module injects a compensation current into the secondary winding. Under the magnetomotive force balance state, the electromagnetic proportional standard unit outputs a standard proportional value according to the turns ratio of the primary winding to the secondary winding and the compensation current. The control and computing unit includes a signal processing module, a pattern discrimination module, a closed-loop control module, and a data fusion module; The signal processing module converts the optical signal into an electrical signal corresponding to the synthesized magnetomotive force; The mode discrimination module determines whether the current working mode is magnetic potential balance mode or measurement difference correction mode based on the electrical signal. In the magnetic potential balance mode, the closed-loop control module drives the current injection module to adjust the compensation current until the synthetic magnetic potential is zero according to the synthetic magnetic potential. In the difference correction mode, the compensation current is kept constant and the measured value of the synthetic magnetic potential is obtained as the deviation. The data fusion module calibrates the measurement coefficient of the optical sensing component using the standard ratio value when the magnetic potential balance mode is in the magnetic core and the magnetic core is in the unsaturated working region. In the difference correction mode, the standard ratio value is corrected by addition or multiplication using the deviation amount to obtain the corrected standard ratio value. The sensor interface unit is connected to the sensor being calibrated, acquires the output signal of the sensor being calibrated, compares it with the corrected standard ratio value, and calculates the measurement error.

2. The high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: The optical sensing component includes fiber optic sensing elements based on the Faraday magneto-optical effect.

3. The high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: The mode discrimination module determines the magnetomotive force balance mode based on the signal-to-noise ratio of the electrical signal, and determines the differential correction mode based on the rate of change of the electrical signal with the primary current.

4. The high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: The magnetic potential balance mode and the differential measurement correction mode share the same hardware architecture, and only the control parameters of the closed-loop control module are changed when switching between the two modes.

5. A high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: The data fusion module performs a self-test procedure during system startup or maintenance. It performs self-monitoring by calibrating the optical sensing component in the magnetic potential balance mode and when the magnetic core is in the unsaturated operating region, and by correcting the proportional deviation of the electromagnetic proportional standard unit in the difference correction mode.

6. The high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: It also includes a temperature compensation module, which monitors the core temperature and the ambient temperature to compensate for the temperature drift of the optical sensing component and the temperature coefficient of the magnetic permeability of the core.

7. The high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: The primary winding includes a plurality of sub-windings distributed along the circumference of the magnetic core, and the plurality of sub-windings constitute a distributed homogenized bus structure.

8. The high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: The control and calculation unit also includes an error calculation module, which calculates the ratio difference at each calibration point by comparing the corrected standard ratio value with the output value of the calibrated sensor.

9. A high-current sensor calibration system based on a DC current ratio standard according to claim 1, characterized in that: The magnetic core is a toroidal iron core.

10. The high-current sensor calibration system based on a DC current ratio standard according to any one of claims 1 to 9, characterized in that: The optical error measurement unit, the electromagnetic proportional standard unit, the control and calculation unit, and the interface unit of the sensor being calibrated are integrated into the same calibration platform to form a closed-loop calibration system.

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