High-precision multi-gear high-current voltage automatic calibration system

Abstract

The invention discloses a high-precision multi-gear large-current voltage automatic calibration system, and the system comprises a current gear switching module which is provided with a plurality of relay groups and is connected with a power input line of a to-be-calibrated device; the primary winding of the multi-tap fluxgate sensor is provided with at least three groups of switchable taps with different gears, and the secondary output of the multi-tap fluxgate sensor is connected with the four-wire system sampling resistor; the calibration mode switching module comprises three groups of relays which are respectively connected with the voltage output end of the four-wire sampling resistor, the output end of the high-precision adjustable voltage source and a voltage sampling wire of the equipment to be calibrated; the input end of the seven-bit and half-bit digital voltmeter is connected with the output end of the calibration mode switching module; a constant temperature control system; the control board is connected with the current gear switching module and the DAC control end of the high-precision adjustable voltage source; and the upper computer is connected with the controller and the communication interface of the seven-bit and half-bit voltmeter.

Description

Technical Field

[0001] The present invention belongs to the technical field of power battery calibration, and in particular relates to a high-precision multi-gear large current and voltage automatic calibration system. Background Art

[0002] With the rapid development of new energy vehicles, energy storage systems, and smart grids, power batteries, as core energy carriers, are facing an increasing demand for performance testing and safety assessment. To more accurately assess the chemical reactions and characteristics within batteries and comprehensively evaluate battery performance, higher requirements are placed on the accuracy of battery testing equipment.

[0003] Battery charge and discharge testing equipment is a crucial component of battery R&D and production. Its core function is to simulate the current, voltage, and temperature changes under actual battery operating conditions, collecting real-time data to assess key parameters such as battery capacity, cycle life, and thermal stability.

[0004] Before battery charge and discharge test equipment leaves the factory, its output current, sampling current, and sampling voltage must be calibrated to meet accuracy specifications. Typically, the accuracy of the calibration equipment must be at least an order of magnitude higher than that of the equipment being calibrated. For more accurate analysis and evaluation of battery performance, higher-precision battery charge and discharge equipment is required. At the same time, this increased equipment accuracy places higher demands on both the calibration equipment and the calibration methods.

[0005] The following are the current calibration methods applicable to power battery charge and discharge test equipment.

[0006] Current calibration method: 1. Shunt-based current calibration: This method connects the shunt in series with the power output line when calibrating the current. A high-bit multimeter is used to read the shunt's voltage value, and the converted current value is used as the actual current value to calibrate the current value sampled by the device itself.

[0007] 2. Current calibration based on Hall effect sensors / fluxgate sensors. This method connects the primary side of the sensor in series with the power output line and the secondary side to a sampling resistor. A high-bit multimeter is used to read the voltage across the sampling resistor. The converted current value is used as the actual current value to calibrate the current value sampled by the device itself.

[0008] Voltage calibration method: 1. Calibration based on constant voltage output: This method places the device in constant voltage output mode when calibrating the voltage. Connect the voltage sampling line and a high-level multimeter to the power output. The high-level multimeter value is used as the actual voltage value to calibrate the voltage value sampled by the device itself.

[0009] 2. Calibration based on a voltage standard source: This method directly connects the voltage sampling line to the voltage standard source when calibrating the voltage, uses the set output of the voltage standard source as the actual voltage value, and calibrates the voltage value sampled by the device itself.

[0010] The defects of the existing technology, for the current calibration method: The accuracy of method 1 is easily affected by temperature when performing large current calibration, and cannot meet the requirements of large current and high precision.

[0011] Method 2 can achieve higher accuracy under high current conditions when using a fluxgate sensor, and its temperature drift and time drift performance are good. However, its accuracy is relative to its maximum range. If the accuracy under different ranges needs to be consistent, it cannot meet the requirements at a range smaller than its range.

[0012] The defects of the existing technology, for the voltage calibration method: Method 1 requires connecting the voltage sampling line and the power output line together, which increases the operation steps. In addition, the control accuracy of the constant voltage output of the equipment may not meet the sampling accuracy requirements, which is not easy to achieve when high-precision calibration is required.

[0013] The voltage accuracy of method 2 depends entirely on the output accuracy of the source meter. If the equipment requires higher accuracy, it is necessary to purchase a source meter with higher accuracy, which will result in high costs.

[0014] For actual use: Generally speaking, voltage and current calibration are performed separately. There are different wiring methods for calibrating voltage and current, which increases the wiring steps.

[0015] Some methods combine the above-mentioned voltage calibration and current calibration together, but the degree of automation is not high, and a small amount of manual line changing operations are still required. In addition, the temperature drift performance of the tooling is not considered much, and the accuracy consistency of multiple calibrations is poor. Summary of the Invention

[0016] In view of this, the main purpose of the present invention is to provide a high-precision multi-speed large current and voltage automatic calibration system.

[0017] To achieve the above object, the technical solution of the present invention is achieved as follows: A high-precision multi-speed large current and voltage automatic calibration system, comprising: The current range switching module is equipped with multiple relay groups and is connected to the power input line of the device to be calibrated. It is used to realize the selection of current channels of different ranges by controlling the relay combination; A multi-tap fluxgate sensor, wherein the primary winding is provided with at least three sets of switchable taps with different gears, and the secondary output is connected to a four-wire sampling resistor; The calibration mode switching module includes three sets of relays, which are respectively connected to the voltage output end of the four-wire sampling resistor, the output end of the high-precision adjustable voltage source, and the voltage sampling line of the device to be calibrated, and are used to automatically switch between the current calibration mode and the voltage calibration mode; A seven-and-a-half-digit digital voltmeter, the input of which is connected to the output of the calibration mode switching module; A constant temperature control system for maintaining a constant temperature in the environment of the four-wire sampling resistor and the high-precision adjustable voltage source; The control board is connected to the current gear switching module and the DAC control terminal of the high-precision adjustable voltage source; The host computer is connected to the communication interface of the controller and the seven-and-a-half-digit voltmeter and is used for calibration process control and data processing. Preferably, the current range switching module includes a first relay group and a second relay group; The first relay group includes a first relay K1.1, a second relay K1.2, and a third relay K1.3, wherein the first relay K1.1, the second relay K1.2, and the third relay K1.3 are respectively connected to the switchable taps of different gears of the fluxgate sensor; The second relay group includes a fourth relay K2, and the fourth relay K2 is connected to the common end of the multi-tap fluxgate sensor at different gears. Preferably, the multi-tap fluxgate sensor 3 includes three groups of switchable taps.

[0018] Preferably, the calibration mode switching module includes a fifth relay K3, a sixth relay K4, and a seventh relay K5; the fifth relay K3 is connected to the voltage signal end of the four-wire sampling resistor; the sixth relay K4 is connected to the output end of the high-precision adjustable voltage source; and the seventh relay K5 is connected to the voltage sampling line of the device to be calibrated.

[0019] Preferably, the four-wire sampling resistor is further connected to a high-precision voltage sampling circuit for replacing a seven-and-a-half-digit digital voltmeter. The rear stage of the high-precision voltage sampling circuit is connected to an ADC, and the digital interface of the ADC is connected to a controller. The high-precision voltage sampling circuit includes a pre-stage filter circuit, an input protection circuit, a first-stage fully differential circuit, a second-stage fully differential circuit, and a post-stage filter circuit, which are connected in sequence.

[0020] Preferably, the pre-stage filter circuit includes a first common-mode filter capacitor C1, a second common-mode filter capacitor C2, a third differential-mode filter capacitor C3, a fourth common-mode filter capacitor C4, a fifth common-mode filter capacitor C5, a first common-mode inductor L1, a first common-mode filter resistor R1, and a second common-mode filter resistor R2; the input voltage Ui is connected to the input protection circuit through the third differential-mode filter capacitor C3 and the first common-mode inductor L1; the positive side of the input voltage Ui is grounded through the first common-mode filter capacitor C1 and the first common-mode filter resistor R1, and is grounded through the fourth common-mode filter capacitor C4, and the negative side is grounded through the second common-mode filter capacitor C2 and the second common-mode filter resistor R2, and is grounded through the fifth common-mode filter capacitor C5; the third differential-mode filter capacitor C3 is connected in parallel between the positive and negative sides of the input voltage Ui.

[0021] Preferably, the input protection circuit includes a first current limiting protection resistor R3, a second current limiting protection resistor R4, a first clamping diode D1, and a second clamping diode D2; one end of the first current limiting protection resistor R3 and the second current limiting protection resistor R4 in parallel are respectively connected to the pre-stage filter circuit, and the other end is respectively connected to the first-stage fully differential circuit, one side of the first current limiting protection resistor R3 is connected to the first clamping diode D1, and one side of the second current limiting protection resistor R4 is connected to the second clamping diode D2.

[0022] Preferably, the first-stage fully differential circuit includes a first operational amplifier U1 and a second operational amplifier U2; the positive pole of the first operational amplifier U1 is correspondingly connected to the input protection circuit, and the negative pole is connected to the second-stage fully differential circuit; the positive pole of the second operational amplifier U2 is correspondingly connected to the input protection circuit, and the negative pole is connected to the second-stage fully differential circuit.

[0023] Preferably, the second-stage fully differential circuit includes a third operational amplifier U3, a fourth operational amplifier U4, a first resistor R5, a second resistor R6, a third resistor R7, a fourth resistor R8, a fifth resistor R9, a sixth resistor R10, a seventh resistor R11, an eighth resistor R12, a first capacitor C6, a second capacitor C7, a third capacitor C8, and a fourth capacitor C9; One path of the negative electrode of the third operational amplifier U3 is connected to the first stage full differential circuit via the first resistor R5, and the other path is connected to the post-stage filter circuit via the seventh resistor R11 and the third capacitor C8 in parallel; one path of the positive electrode is connected between the third resistor R7 and the first stage full differential circuit via the second resistor R6, and the other path is connected to the fifth resistor R9 and the first capacitor C6 in parallel. ; One path of the negative electrode of the fourth operational amplifier U4 is connected to the first stage full differential circuit via the third resistor R7, and the other path is connected to the post-stage filter circuit via the eighth resistor R12 and the fourth capacitor C9 in parallel; one path of the positive electrode is connected between the second resistor R6 and the first stage full differential circuit via the fourth resistor R8, and the other path is connected to the sixth resistor R10 and the second capacitor C7 in parallel. .

[0024] Preferably, the post-stage filter circuit includes a ninth resistor R13, a tenth resistor R14, and a fifth capacitor C10; One end of the ninth resistor R13 is connected to the second stage full differential circuit, and the other end outputs the voltage ; One end of the tenth resistor R14 is connected to the second stage full differential circuit, and the other end outputs the voltage ; The fifth capacitor C10 is connected between the ninth resistor R13 and the tenth resistor R14.

[0025] Compared with the prior art, the present invention has the following beneficial effects: The present invention can achieve high-precision calibration in a wide current range and high-precision calibration of voltage sampling circuits, while ensuring the consistency of accuracy under multiple ranges, with simple wiring, truly realizing full automation of the calibration process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings described herein are used to further understand the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 A system block diagram of a high-precision multi-gear large current and voltage automatic calibration system is provided for an embodiment of the present invention; Figure 2 Provided is a current gear switching logic diagram of a current gear switching module in a high-precision multi-gear large current and voltage automatic calibration system according to an embodiment of the present invention; Figure 3 Provided is a calibration mode switching logic diagram of a calibration mode switching module in a high-precision multi-gear large current and voltage automatic calibration system according to an embodiment of the present invention; Figure 4 A schematic diagram of a high-precision adjustable voltage source circuit in a high-precision multi-gear large current and voltage automatic calibration system is provided for an embodiment of the present invention; Figure 5 A graph showing the change of a certain output value of a high-precision adjustable voltage source over time in a high-precision multi-gear large current and voltage automatic calibration system is provided in accordance with an embodiment of the present invention; Figure 6A circuit diagram of a high-precision voltage sampling circuit in a high-precision multi-gear large current and voltage automatic calibration system is provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] The same or similar numbers in the drawings of this embodiment correspond to the same or similar parts; in the description of the present invention, it should be understood that the terms "upper", "lower", "left", "right", "inner", "outer", etc. indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0029] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, article, or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, article, or device comprising the element.

[0030] The embodiment of the present invention provides a high-precision multi-speed large current and voltage automatic calibration system, such as Figure 1 As shown, it includes: a current gear switching module 2, which is configured with multiple relay groups and connected to the power input line 1 of the device to be calibrated, and is used to realize the selection of current channels of different ranges by controlling the relay combination; A multi-tap fluxgate sensor 3, whose primary winding is provided with at least three sets of switching taps of different gears, and the secondary output is connected to a four-wire sampling resistor 4; The calibration mode switching module 6 includes three sets of relays, which are respectively connected to the voltage output end of the four-wire sampling resistor, the output end of the high-precision adjustable voltage source 10, and the voltage sampling line 5 of the device to be calibrated, and are used to automatically switch between the current calibration mode and the voltage calibration mode; A seven-and-a-half-digit digital voltmeter 7, the input end of which is connected to the output end of the calibration mode switching module; A constant temperature control system 11 is used to maintain a constant temperature in the environment of the four-wire sampling resistor 4 and the high-precision adjustable voltage source 10; The controller 9 is connected to the current gear switching module 2, the DAC digital control terminal of the high-precision adjustable voltage source 10, and the communication interface of the seven-and-a-half-digit voltmeter 7; The host computer 12 is connected to the communication interface of the controller 9 and the seven-and-a-half-digit voltmeter 7 and is used for calibration process control and data processing. The present invention can fully automatically realize 50ppm precise calibration under multiple gears and 50ppm precise calibration of the voltage sampling circuit, and has small temperature drift and time drift.

[0031] The current gear switching module 2 includes a first relay group and a second relay group; The first relay group includes a first relay K1.1, a second relay K1.2, and a third relay K1.3, and the first relay K1.1, the second relay K1.2, and the third relay K1.3 are respectively connected to the common taps of different gears of the fluxgate sensor; The second relay group includes a fourth relay K2, and the fourth relay K2 is connected to the common terminal of the fluxgate. like Figure 2 As shown, the power line of the device under test is connected to the current range switching part. Multiple relays can be set in the range switching part. The figure takes 4 as an example. Among them, K1.1, K1.2, and K1.3 are connected to the same node as a group, and K2 is a group. Four wires are led out from the four output terminals and connected to the multi-tap fluxgate sensor 3. The control logic signal of the relay is given by the controller.

[0032] The multi-tap fluxgate sensor 3 includes three groups of switchable taps.

[0033] Specifically, the primary turns ratio corresponding to the three sets of switchable taps here can be determined by the specific required gear. Which gear needs to be switched to which gear, and a four-wire sampling resistor is shared. The so-called four-wire sampling resistor is not two resistance values. In order to improve the measurement accuracy, the four wires used in the Kelvin measurement method are used. It is a fixed resistance value and is used to convert the current on the secondary side of the sensor into a voltage. For example, assuming that the number of turns on the secondary side of the sensor is 400 and the rated current of the secondary side is 200mA, if the number of turns corresponding to the three sets of taps on the primary side of the sensor is 1 turn, 2 turns, and 4 turns, then the three ranges of 80A, 40A, and 20A can be covered and calibrated.

[0034] Connect one end of the three taps together and connect them to the K2 output of the gear switching part, and the other ends to the outputs of K1.1, K1.2, and K1.3 respectively. In this way, three gear outputs are generated using one fluxgate sensor.

[0035] The current signal output from the secondary side of the multi-tap fluxgate sensor 3 is connected to the power input line of the four-wire sampling resistor 4. In order to improve the sampling accuracy, the sampling resistor adopts a four-wire, low-resistance, low-temperature drift and time drift resistor. The voltage across the sampling resistor is connected to the calibration mode switching module 6 through the sampling line of the four-wire sampling resistor 4.

[0036] The calibration mode switching module 6 includes a fifth relay K3, a sixth relay K4, and a seventh relay K5; the fifth relay K3 is connected to the voltage signal end of the four-wire sampling resistor 4; the sixth relay K4 is connected to the output end of the high-precision adjustable voltage source 10; and the seventh relay K5 is connected to the voltage sampling line 5 of the device to be calibrated.

[0037] like Figure 3 As shown, the voltage across the four-wire sampling resistor 4 is connected to switches K3.1 and K3.2, the high-precision adjustable voltage source 10 is connected to K4.1 and K4.2, and the voltage sampling line of the calibrated device is connected to switches K5.1 and K5.2. The positive output terminals of the three switch groups are connected to one terminal, the negative output terminals to the other terminal, and the output is connected to the input port of a 7.5-digit voltmeter 7.

[0038] like Figure 4 As shown, the high-precision adjustable voltage source 10 is mainly composed of a high-bit DAC, a reference chip, and an operational amplifier. The DAC receives the digital signal output by the controller and converts it into an analog signal, which is output through impedance conversion via a follower.

[0039] In this invention patent, in order to meet the requirements of high-performance voltage source output, special attention needs to be paid to its model selection. Specifically, the DAC is required to have high resolution, excellent integral nonlinearity, low noise, and low temperature drift. The reference is required to be a high-performance reference with low noise, low temperature drift, and time drift. Commonly selected models include but are not limited to LTZ1000, ADR1000, LM399, etc. The follower requires a low-noise, low-offset voltage operational amplifier. Commonly selected models include but are not limited to OP07, ADA4522, ADA4523, etc.

[0040] In order to reduce the temperature drift of the detection system, the four-wire sampling resistor 4 and the high-precision adjustable voltage source 10 are placed in a constant temperature system 11, and a constant temperature controller is used for constant temperature control.

[0041] The controller 9 receives signals from the host computer 12 and switches the relays in the system according to the needs. The 7.5-digit voltmeter 7 communicates with the host computer 12 to realize the transmission of calibration data. In addition, the automatic calibration system is also compatible with manual mode control, which is convenient for some special occasions.

[0042] Before calibration, the power input line 1 and voltage sampling line 5 of the device to be calibrated are connected to the system. Thereafter, the calibration mode is selected through the operation of the host computer 12, and the automatic calibration is completed through the logic control of the controller 9.

[0043] Specifically, during current calibration, relay K2 is closed. Based on the current range of the device being calibrated, the corresponding relay in K1 is automatically selected and closed. The two relays in K3 are closed, the two relays in K4 are disconnected, and the two relays in K5 are short-circuited and connected to ground. The device being calibrated is now controlled to output a constant current, resulting in a voltage value in the 7.5-digit voltmeter 7. This voltage value is then output to the host computer 12 for processing. This operation is repeated at multiple points across the full range. Calibration parameters are calculated based on the current sampled by the device being calibrated and updated to the device being calibrated, completing current calibration.

[0044] During voltage calibration, the three relays in K1 are disconnected, relays K2 and K3 are disconnected, and relays K4 and K5 are closed. The voltage sampling circuit of the device being calibrated is now connected to the high-precision adjustable voltage source and to the 7.5-digit voltmeter 7. Since the voltage sampling line 5 of the device being calibrated and the input of the 7.5-digit voltmeter 7 are typically in a high-impedance state, the output accuracy of the high-precision adjustable voltage source 10 is not affected. At this point, controller 9, based on instructions from host computer 12, controls the high-precision adjustable voltage source 10 to output a constant voltage. A voltage value is obtained in both the 7.5-digit voltmeter 7 and the device being calibrated. Host computer 12 records these two voltage values. This operation is repeated at multiple points across the full range. The host computer automatically calculates calibration parameters based on the data and updates them to the device being calibrated, completing voltage calibration.

[0045] Using this technical solution, the calibration fixture achieves 1ppm accuracy at multiple current levels, and the adjustable voltage source output achieves 1ppm accuracy. The seven-and-a-half-digit calibration tool can effectively resolve voltage changes as small as 1ppm, meeting the requirements for 50ppm current and voltage accuracy for high-precision battery testing equipment at multiple current levels. Furthermore, the tool offers convenient wiring and a high degree of automation, significantly improving equipment calibration efficiency.

[0046] Taking the eight-and-a-half-digit detection current as the standard and comparing it with the current measured by the calibration system of the present invention, the test data of three points are as follows: like Figure 5 As shown, the adjustable voltage source proposed in the present invention is set to output 3.68466V and tested for about 15 minutes using a 7.5-digit voltmeter 7. The waveform is as follows. The adjustable voltage source has an output accuracy within 1ppm and good stability, which can meet the needs of high-precision voltage calibration.

[0047] Furthermore, in order to reduce costs, the seven-and-a-half-digit voltmeter 7 can also be replaced by a high-precision sampling circuit 13 , the rear stage of the high-precision voltage sampling circuit 13 is connected to an ADC, and the digital interface of the ADC is connected to the controller 9 .

[0048] The high-precision voltage sampling circuit 13 includes a pre-stage filter circuit 131 , an input protection circuit 132 , a first-stage fully differential circuit 133 , a second-stage fully differential circuit 134 , and a post-stage filter circuit 135 , which are connected in sequence.

[0049] The high-precision voltage sampling circuit 13 can achieve high-precision detection and voltage detection over a wide current range, while ensuring the consistency of accuracy under multiple ranges. It has a relatively simple sampling circuit and has the characteristics of small temperature drift and time drift. The circuit has a lower cost and has a detection function similar to that of a seven-and-a-half-digit voltmeter.

[0050] The pre-stage filter circuit 131 includes a first common-mode filter capacitor C1, a second common-mode filter capacitor C2, a third differential-mode filter capacitor C3, a fourth common-mode filter capacitor C4, a fifth common-mode filter capacitor C5, a first common-mode inductor L1, a first common-mode filter resistor R1, and a second common-mode filter resistor R2; the input voltage Ui is connected to the input protection circuit 132 through the third differential-mode capacitor C3 and the first common-mode inductor L1; the positive side of the input voltage Ui is connected to ground through the first common-mode filter capacitor C1 and the first common-mode filter resistor R1, and then to ground through the fourth common-mode filter capacitor C4, and the negative side is connected to ground through the second common-mode filter capacitor C2 and the second common-mode filter resistor R2, and then to ground through the fifth common-mode filter capacitor C5; the third differential-mode filter capacitor C3 is connected in parallel between the positive and negative sides of the input voltage Ui.

[0051] Specifically, the first common-mode filter capacitor C1, the second common-mode filter capacitor C2, the fourth common-mode filter capacitor C4, the fifth common-mode filter capacitor C5 satisfies C1 = C2, C4 = C5; The first common-mode inductor L1 is used to filter out common-mode interference introduced into the measurement circuit. The first common-mode filter resistor R1 and the second common-mode filter resistor R2, where R1=R2, are used to reduce current overshoot in the common-mode circuit. The function of the third differential mode filter capacitor C3 is to filter out differential mode interference introduced into the measurement circuit.

[0052] The input protection circuit 132 includes a first current limiting protection resistor R3, a second current limiting protection resistor R4, a first clamping diode D1, and a second clamping diode D2; one end of the first current limiting protection resistor R3 and the second current limiting protection resistor R4 in parallel are respectively connected to the pre-stage filter circuit 131, and the other end is respectively connected to the first-stage fully differential circuit 133, one side of the first current limiting protection resistor R3 is connected to the first clamping diode D1, and one side of the second current limiting protection resistor R4 is connected to the second clamping diode D2.

[0053] Specifically, the first current limiting protection resistor R3 and the second current limiting protection resistor R4, R3=R4, are used to suppress the current impact in the input path and prevent excessive current from being injected and damaging the subsequent circuit. The first clamping diode D1 and the second clamping diode D2 function to clamp the voltage on the input path to prevent the voltage from exceeding the power supply voltage of the subsequent circuit and causing the subsequent circuit to malfunction.

[0054] The first-stage fully differential circuit 133 includes a first operational amplifier U1 and a second operational amplifier U2; the positive pole of the first operational amplifier U1 is connected to the input protection circuit 132, and the negative pole is connected to the second-stage fully differential circuit 134; the positive pole of the second operational amplifier U2 is connected to the input protection circuit 132, and the negative pole is connected to the second-stage fully differential circuit 134.

[0055] Specifically, the first operational amplifier U1 and the second operational amplifier U2 are selected to have the characteristics of large input impedance, small offset current and bias current, and are used as followers to achieve impedance transformation, increase input resistance, make the input voltage closer to the measured voltage, reduce output resistance, and make the output voltage more accurately transmitted to the next stage.

[0056] The second-stage fully differential circuit 134 includes a third operational amplifier U3, a fourth operational amplifier U4, a first resistor R5, a second resistor R6, a third resistor R7, a fourth resistor R8, a fifth resistor R9, a sixth resistor R10, a seventh resistor R11, an eighth resistor R12, a first capacitor C6, a second capacitor C7, a third capacitor C8, and a fourth capacitor C9; The negative electrode of the third operational amplifier U3 is connected to the first-stage fully differential circuit 133 via the first resistor R5, and the other path is connected to the post-stage filter circuit 135 via the seventh resistor R11 and the third capacitor C8 in parallel; the positive electrode is connected between the third resistor R7 and the first-stage fully differential circuit 133 via the second resistor R6, and the other path is connected to the fifth resistor R9 and the first capacitor C6 in parallel. ; The negative electrode of the fourth operational amplifier U4 is connected to the first-stage fully differential circuit 133 via the third resistor R7, and the other path is connected to the post-stage filter circuit 135 via the eighth resistor R12 and the fourth capacitor C9 in parallel; the positive electrode is connected between the second resistor R6 and the first-stage fully differential circuit 133 via the fourth resistor R8, and the other path is connected to the sixth resistor R10 and the second capacitor C7 in parallel. .

[0057] Specifically, the third operational amplifier U3 and the fourth operational amplifier U4 are selected to have the characteristics of low noise, small offset voltage and small offset voltage drift, and are used as differential operational amplifiers to achieve signal bias processing and amplification; The first resistor R5, the second resistor R6, the third resistor R7, and the fourth resistor R8, R5=R6=R7=R8, and the fifth resistor R9, the sixth resistor R10, the seventh resistor R11, and the eighth resistor R12, R9=R10=R11=R12, are all selected to have excellent temperature drift and time drift performance; The first capacitor C6, the second capacitor C7, the third capacitor C8, and the fourth capacitor C9, C6=C7=C8=C9, R9, C6 and R10, C7 are connected to , which acts as a superposition of an offset on the two input signals , to meet the input requirements of the subsequent high-bit ADC.

[0058] The post-stage filter circuit 135 includes a ninth resistor R13, a tenth resistor R14, and a fifth capacitor C10; One end of the ninth resistor R13 is connected to the second-stage fully differential circuit 134, and the other end outputs a voltage ; One end of the tenth resistor R14 is connected to the second-stage fully differential circuit 134, and the other end outputs a voltage ; The fifth capacitor C10 is connected between the ninth resistor R13 and the tenth resistor R14.

[0059] Specifically, the ninth resistor R13, the tenth resistor R14, R13=R14, and the fifth capacitor C10 form a low-pass filter circuit to further filter the signal.

[0060] After high-precision voltage sampling circuit, the input voltage and output voltage Satisfies the following relationship .

[0061] The output of the high-precision voltage sampling circuit is connected to the ADC, and digital signal transmission is achieved between the controller and the ADC to achieve signal acquisition and processing. For current inputs of different gears, after being processed by the sampling circuit and ADC and converted in the controller, the accuracy of each gear can be achieved at the same level. For example, the primary side of the sensor has two gears, a and b, whose rated current outputs are x and 2x respectively, and the corresponding secondary side rated outputs are both y. After passing through the sampling resistor, sampling circuit, and ADC, the signals received by the controller are consistent. The controller multiplies the received signals by the corresponding multiples according to the gear. If the corresponding multiplication of gear a is 1 times, then gear b is multiplied by 2 times. The final processed signals of each gear have the same accuracy level. This method can meet the consistency of accuracy under multiple gears by using a common sampling circuit, reducing the complexity of the sampling circuit.

[0062] By adopting the above technical solution, multi-level current measurement and high-precision voltage measurement have been realized. The measurement accuracy is within 50ppm compared with the test results of an 8.5-digit multimeter, and the measurement time drift and temperature drift performance are good, proving its removable properties for a 7.5-digit voltmeter.

[0063] Taking the eight-and-a-half-bit detection current as the standard, the proposed method is compared with the detection current. The test data are as follows: The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention.

Claims

1. A high-precision multi-speed large current and voltage automatic calibration system, characterized in that: include: The current range switching module is equipped with multiple relay groups and is connected to the power input line of the device to be calibrated. It is used to realize the selection of current channels of different ranges by controlling the relay combination; A multi-tap fluxgate sensor, wherein the primary winding is provided with at least three sets of switchable taps with different gears, and the secondary output is connected to a four-wire sampling resistor; The calibration mode switching module includes three sets of relays, which are respectively connected to the voltage output end of the four-wire sampling resistor, the output end of the high-precision adjustable voltage source, and the voltage sampling line of the device to be calibrated, and are used to automatically switch between the current calibration mode and the voltage calibration mode; A seven-and-a-half-digit digital voltmeter, the input of which is connected to the output of the calibration mode switching module; A constant temperature control system for maintaining a constant temperature in the environment of the four-wire sampling resistor and the high-precision adjustable voltage source; The control board is connected to the current gear switching module and the DAC control terminal of the high-precision adjustable voltage source; The host computer is connected to the communication interface of the controller and the seven-and-a-half-digit voltmeter and is used for calibration process control and data processing.

2. The high-precision multi-gear large current and voltage automatic calibration system according to claim 1 is characterized in that: The current gear switching module includes a first relay group and a second relay group; The first relay group includes a first relay K1.1, a second relay K1.2, and a third relay K1.3, wherein the first relay K1.1, the second relay K1.2, and the third relay K1.3 are respectively connected to the switchable taps of different gears of the fluxgate sensor; The second relay group includes a fourth relay K2, and the fourth relay K2 is connected to the common end of the multi-tap fluxgate sensor at different gears.

3. The high-precision multi-gear large current and voltage automatic calibration system according to claim 1 or 2, characterized in that: The multi-tap fluxgate sensor 3 includes three groups of switchable taps.

4. The high-precision multi-gear large current and voltage automatic calibration system according to claim 3 is characterized in that: The calibration mode switching module includes a fifth relay K3, a sixth relay K4, and a seventh relay K5; the fifth relay K3 is connected to the voltage signal end of the four-wire sampling resistor; the sixth relay K4 is connected to the output end of the high-precision adjustable voltage source; and the seventh relay K5 is connected to the voltage sampling line of the device to be calibrated.

5. The high-precision multi-gear large current and voltage automatic calibration system according to claim 1 is characterized in that: The four-wire sampling resistor is also connected to a high-precision voltage sampling circuit for replacing a seven-and-a-half-digit digital voltmeter. The rear stage of the high-precision voltage sampling circuit is connected to an ADC, and the digital interface of the ADC is connected to a controller. The high-precision voltage sampling circuit includes a pre-stage filter circuit, an input protection circuit, a first-stage fully differential circuit, a second-stage fully differential circuit, and a post-stage filter circuit, which are connected in sequence.

6. The high-precision multi-gear large current and voltage automatic calibration system according to claim 5, characterized in that: The pre-stage filter circuit includes a first common-mode filter capacitor C1, a second common-mode filter capacitor C2, a third differential-mode filter capacitor C3, a fourth common-mode filter capacitor C4, a fifth common-mode filter capacitor C5, a first common-mode inductor L1, a first common-mode filter resistor R1, and a second common-mode filter resistor R2; the input voltage Ui is connected to the input protection circuit through the third differential-mode filter capacitor C3 and the first common-mode inductor L1; the positive side of the input voltage Ui is grounded through the first common-mode filter capacitor C1 and the first common-mode filter resistor R1, and is grounded through the fourth common-mode filter capacitor C4, and the negative side is grounded through the second common-mode filter capacitor C2 and the second common-mode filter resistor R2, and is grounded through the fifth common-mode filter capacitor C5; the third differential-mode filter capacitor C3 is connected in parallel between the positive and negative sides of the input voltage Ui.

7. The high-precision multi-gear large current and voltage automatic calibration system according to claim 6, characterized in that: The input protection circuit includes a first current limiting protection resistor R3, a second current limiting protection resistor R4, a first clamping diode D1, and a second clamping diode D2; one end of the first current limiting protection resistor R3 and the second current limiting protection resistor R4 connected in parallel are respectively connected to the pre-stage filter circuit, and the other end is respectively connected to the first-stage fully differential circuit, one side of the first current limiting protection resistor R3 is connected to the first clamping diode D1, and one side of the second current limiting protection resistor R4 is connected to the second clamping diode D2.

8. The high-precision multi-gear large current and voltage automatic calibration system according to claim 7, characterized in that: The first-stage fully differential circuit includes a first operational amplifier U1 and a second operational amplifier U2; the positive pole of the first operational amplifier U1 is connected to the input protection circuit, and the negative pole is connected to the second-stage fully differential circuit; the positive pole of the second operational amplifier U2 is connected to the input protection circuit, and the negative pole is connected to the second-stage fully differential circuit.

9. The high-precision multi-gear large current and voltage automatic calibration system according to claim 8, characterized in that: The second-stage fully differential circuit includes a third operational amplifier U3, a fourth operational amplifier U4, a first resistor R5, a second resistor R6, a third resistor R7, a fourth resistor R8, a fifth resistor R9, a sixth resistor R10, a seventh resistor R11, an eighth resistor R12, a first capacitor C6, a second capacitor C7, a third capacitor C8, and a fourth capacitor C9; One path of the negative electrode of the third operational amplifier U3 is connected to the first stage full differential circuit via the first resistor R5, and the other path is connected to the post-stage filter circuit via the seventh resistor R11 and the third capacitor C8 in parallel; one path of the positive electrode is connected between the third resistor R7 and the first stage full differential circuit via the second resistor R6, and the other path is connected to the fifth resistor R9 and the first capacitor C6 in parallel. ; One path of the negative electrode of the fourth operational amplifier U4 is connected to the first stage full differential circuit via the third resistor R7, and the other path is connected to the post-stage filter circuit via the eighth resistor R12 and the fourth capacitor C9 in parallel; one path of the positive electrode is connected between the second resistor R6 and the first stage full differential circuit via the fourth resistor R8, and the other path is connected to the sixth resistor R10 and the second capacitor C7 in parallel. .

10. The high-precision multi-gear large current and voltage automatic calibration system according to claim 9, characterized in that: The post-stage filter circuit includes a ninth resistor R13, a tenth resistor R14, and a fifth capacitor C10; One end of the ninth resistor R13 is connected to the second stage full differential circuit, and the other end outputs the voltage ; One end of the tenth resistor R14 is connected to the second stage full differential circuit, and the other end outputs the voltage ; The fifth capacitor C10 is connected between the ninth resistor R13 and the tenth resistor R14.

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