Calibration circuit and calibration method for breakdown current of electrical stability tester

Abstract

The invention discloses a calibration circuit and a calibration method for breakdown current of an electrical stability tester. The calibration circuit comprises a current measurement module, a controller module and a variable resistance module, a first input end of the variable resistance module is connected with the electrical stability tester, a second input end is connected with the controller module, and an output end is connected with the current measurement module; a first input end of the current measurement module is connected with the electrical stability tester, a second input end is connected with the variable resistance module, an output end is connected with the controller module, and the current measurement module is used for measuring loop current of a closed loop formed by the variable resistance module and the current measurement module and outputting the measured loop current to the controller module; and the controller module is used for sending a control signal to the variable resistance module according to the magnitude of the loop current and the magnitude of the breakdown current corresponding to the reference voltage output by the electrical stability tester, so that the magnitude of the variable resistance module is changed until the electrical stability tester alarms breakdown.

Description

Technical Field

[0001] The invention relates to the technical field of electric stability testers, and in particular to a calibration circuit and a calibration method for breakdown current of an electric stability tester. Background Art

[0002] The electrical stability tester (emulsion breaking voltage tester) is a special device for measuring the point stability (ES) parameters of oil-based drilling fluids. Its measurement accuracy is directly related to the reliability of parameters related to the stability of the oil-based drilling fluid emulsion and oil wettability. The current calibration of the breakdown current value parameters of the electrical stability tester is based on GBT 16783.2. The calibration of the tester mainly uses standard resistors and / or Zener diodes, where standard resistors are used to check the ratio of voltage reading to breakdown current, and Zener diodes are used to directly check the voltage value. The resistor and diode are used simultaneously for calibration. Since it is usually necessary to conduct periodic tests and judge the electrical stability of oil-based drilling fluid based on the change trend of ES when examining the electrical stability of oil-based drilling fluid, and the upper limit of the output voltage of the electrical stability tester is 2000V or even higher, it is necessary to calibrate its breakdown current value at different output voltages within the entire range when calibrating the electrical stability tester. Usually, at least 5 points are taken for calibration respectively, and at least 5 corresponding physical resistors are prepared. The corresponding physical resistor is selected according to the selected test voltage during calibration; furthermore, since the maximum output voltage of the tester is high, low-voltage resistors and high-voltage resistors need to be prepared separately during calibration to avoid excessive output power of the tester and improper selection of resistors during calibration, which may cause breakdown of resistors. Therefore, if physical resistors are used to calibrate the breakdown current of the electrical stability tester, not only do you need to manually select the physical resistors, but you also need to pay attention to the selection of high and low voltage resistors. The whole process is more troublesome, the workload is large, and it is not easy to operate. Summary of the invention

[0003] The invention provides a calibration circuit and a calibration method for the breakdown current of an electrical stability tester, so as to solve the technical problem in the prior art that the breakdown current of the stability tester is calibrated manually by selecting a physical resistance, which results in a cumbersome selection process, a large workload and difficulty in operation.

[0004] The embodiment of the present invention provides a calibration circuit for breakdown current of an electric stability tester, including a current measurement module, a controller module and a variable resistance module; The first input end of the variable resistance module is connected to the electric stability tester, the second input end is connected to the controller module, and the output end is connected to the current measurement module; The first input end of the current measurement module is connected to the electric stability tester, the second input end is connected to the variable resistance module, and the output end is connected to the controller module, and is used to measure the loop current of the closed loop formed by the electric stability tester, the variable resistance module and the current measurement module, and output the measured loop current to the controller module; The controller module is used to send a control signal to the variable resistor module according to the loop current and the breakdown current corresponding to the reference voltage output by the electrical stability tester, thereby changing the size of the variable resistor module until the electrical stability tester alarms for breakdown.

[0005] In an optional embodiment of the present application, the current measurement module is composed of a current detection resistor , differential operational amplifier A2, true effective value conversion circuit and analog-to-digital conversion circuit ADC; Current Sense Resistor One end of the current detection resistor is connected to the 2nd foot of the primary end of the transformer T in the variable resistor module. The other end is returned to the output of the tester, and the non-inverting end of the operational amplifier A2 is connected to the current sensing resistor The inverting terminal of operational amplifier A2 is connected to the 2nd pin of the primary terminal of transformer T. At the other end, the output end of the operational amplifier A2 is connected to the input end of the true effective value conversion circuit, the output end of the true effective value circuit is connected to the input end of the analog-to-digital conversion circuit ADC, and the digital output end of the ADC is interconnected with the controller module.

[0006] In an optional embodiment of the present application, the controller module is a single chip microcomputer or an ARM or an FPGA.

[0007] In an optional embodiment of the present application, the variable resistance module is composed of a transformer T, a first diode D1, a second diode D2, a first voltage divider resistor , the second voltage divider resistor , operational amplifier A1, MOS tube, digital-to-analog conversion circuit DAC and sampling resistor composition; The primary end 1 pin of the transformer T is connected to the output end of the electrical stability tester, the secondary end 3 pin of the transformer T is connected to the positive electrode of the first diode D1, the secondary end 5 pin of the transformer T is connected to the positive electrode of the second diode D2, the secondary end 4 pin of the transformer T is grounded, the cathode of the first diode D1 is connected to the cathode of the second diode D2 and connected to the first voltage divider resistor One end and the drain of the MOS tube, the first voltage divider resistor The other end is connected to the non-inverting terminal of operational amplifier A1 and the second voltage divider resistor One end of the second voltage divider resistor The other end is grounded, the output end of the operational amplifier A1 is connected to the gate of the MOS tube, and the source of the MOS tube is connected to the input reference voltage end of the digital-to-analog conversion circuit DAC and the sampling resistor One end of the sampling resistor The other end of is grounded, the control signal end of the digital-to-analog conversion circuit DAC is connected to the controller module output, and the output end of the digital-to-analog conversion circuit DAC is connected to the inverting end of the operational amplifier A1.

[0008] In an optional embodiment of the present application, the output end of the controller module outputs a correction signal to the variable resistance module according to the loop current and the breakdown current corresponding to the reference voltage output by the electrical stability tester, including: When the loop current is less than the breakdown current corresponding to the output reference voltage of the electrical stability tester, the controller module sends a control signal to the variable resistance module to reduce the control word, so that the variable resistance module increases the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by reducing the variable electronic load resistance; When the loop current is greater than the breakdown current corresponding to the output reference voltage of the electrical stability tester, the controller module sends a control signal to the variable resistance module to increase the control word, so that the variable resistance module increases the variable electronic load resistance to reduce the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester.

[0009] In an optional embodiment of the present application, the relationship between the variable electronic load resistance and the control word is expressed as follows: in, is a variable electronic load resistor; is the control word; N is the number of bits of resolution of the controller module.

[0010] The embodiment of the present invention provides a method for calibrating the breakdown current of an electric stability tester, which is applied to the calibration circuit of the breakdown current of the electric stability tester. The calibration method includes: By changing the size of the variable resistor, the loop current of the closed loop formed by the variable resistor module and the current measurement module is adjusted until the electrical stability tester alarms; Recording the instantaneous current at the moment when the electrical stability tester gives an alarm, and using the instantaneous current as the breakdown current of the electrical stability tester; According to the loop current and the breakdown current, the breakdown current of the electrical stability tester is calibrated by adjusting the variable electronic load resistor in the variable resistor module. In an optional embodiment of the present application, the calibration of the breakdown current of the electrical stability tester by adjusting the variable electronic load resistor in the variable resistor module includes: When the loop current is less than the breakdown current corresponding to the output reference voltage of the electrical stability tester, a correction signal is output to reduce the control word so as to increase the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by reducing the variable electronic load resistance.

[0011] In an optional embodiment of the present application, the calibration of the breakdown current of the electrical stability tester by adjusting the variable electronic load resistance in the variable resistance module includes: When the loop current is greater than the breakdown current corresponding to the output reference voltage of the electrical stability tester, a correction signal is output to increase the control word so as to reduce the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by increasing the variable electronic load resistance.

[0012] In an optional embodiment of the present application, the relationship between the variable electronic load resistance and the control word is expressed as follows: in, is a variable electronic load resistor; is the control word; N is the number of bits of resolution of the controller module; is the first voltage-dividing resistor; is the second voltage-dividing resistor; Sampling resistor.

[0013] The beneficial effect of the present invention is that the present invention automatically adjusts the variable electronic load according to different output voltage values ​​of the electrical stability tester, so that the loop current slowly increases to the breakdown current value, saves costs, is easy to operate, improves work efficiency, and overcomes the large uncertainty caused by the use of physical resistance and peak current meter measurement. It can also provide important technical support for the calibration of such instruments by metrology and verification institutions and the formulation of future regulations or specifications, and also provide important technical guarantees for the electrical stability assessment of oil-based drilling fluids in the petroleum industry, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a schematic diagram of the breakdown current calibration of the electrical stability tester provided by the present invention; Figure 2 The present invention provides a schematic diagram of the principle of a calibration circuit for a breakdown current of an electrical stability tester. DETAILED DESCRIPTION

[0014] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In the subsequent description, the use of suffixes such as "module", "component" or "unit" used to represent elements is only to facilitate the description of the present invention and has no specific meaning in itself. Therefore, "module", "component" or "unit" can be used in a mixed manner.

[0015] An embodiment of the present invention provides a calibration circuit for the breakdown current of an electrical stability tester, comprising a current measuring module, a controller module and a variable resistor module; the first input end of the variable resistor module is connected to the electrical stability tester, the second input end is connected to the controller module, and the output end is connected to the current measuring module; the first input end of the current measuring module is connected to the electrical stability tester, the second input end is connected to the variable resistor module, and the output end is connected to the controller module, and is used to measure the loop current of a closed loop formed by the variable resistor module and the current measuring module, and output the measured loop current to the controller module; the controller module is used to send a control signal to the variable resistor module according to the size of the breakdown current corresponding to the loop current and the reference voltage output by the electrical stability tester, thereby changing the size of the resistance of the variable resistor module until the electrical stability tester alarms a breakdown.

[0016] In an optional embodiment of the present application, the current measurement module is composed of a current detection resistor , differential operational amplifier A2, true effective value conversion circuit and analog-to-digital conversion circuit ADC; current detection resistor One end of the current detection resistor is connected to the 2nd foot of the primary end of the transformer T in the variable resistor module. The other end is returned to the output of the tester, and the non-inverting end of the operational amplifier A2 is connected to the current sensing resistor The inverting terminal of operational amplifier A2 is connected to the 2nd pin of the primary terminal of transformer T. At the other end, the output end of the operational amplifier A2 is connected to the input end of the true effective value conversion circuit, the output end of the true effective value circuit is connected to the input end of the analog-to-digital conversion circuit ADC, and the digital output end of the ADC is interconnected with the controller module.

[0017] In an optional embodiment of the present application, the controller module is a single chip microcomputer or an ARM or an FPGA.

[0018] In an optional embodiment of the present application, the variable resistance module is composed of a transformer T, a first diode D1, a second diode D2, a first voltage divider resistor , the second voltage divider resistor , operational amplifier A1, MOS tube, digital-to-analog conversion circuit DAC and sampling resistor Composition: The primary end 1 pin of the transformer T is connected to the output end of the electrical stability tester, the secondary end 3 pin of the transformer T is connected to the positive electrode of the first diode D1, the secondary end 5 pin of the transformer T is connected to the positive electrode of the second diode D2, the secondary end 4 pin of the transformer T is grounded, the cathode of the first diode D1 is connected to the cathode of the second diode D2 and connected to the first voltage divider resistor One end and the drain of the MOS tube, the first voltage divider resistor The other end is connected to the non-inverting terminal of operational amplifier A1 and the second voltage divider resistor One end of the second voltage divider resistor The other end is grounded, the output end of the operational amplifier A1 is connected to the gate of the MOS tube, and the source of the MOS tube is connected to the input reference voltage end of the digital-to-analog conversion circuit DAC and the sampling resistor One end of the sampling resistor The other end of is grounded, the control signal end of the digital-to-analog conversion circuit DAC is connected to the controller module output, and the output end of the digital-to-analog conversion circuit DAC is connected to the inverting end of the operational amplifier A1.

[0019] In an optional embodiment of the present application, the output end of the controller module sends a control signal to the variable resistance module according to the magnitude of the breakdown current corresponding to the loop current and the reference voltage output by the electrical stability tester, including: when the loop current is less than the breakdown current corresponding to the reference voltage output by the electrical stability tester, the controller module sends a control signal of reducing the control word to the variable resistance module, so that the variable resistance module increases the loop current to the breakdown current corresponding to the reference voltage output by the electrical stability tester by reducing the variable electronic load resistance; when the loop current is greater than the breakdown current corresponding to the reference voltage output by the electrical stability tester, the controller module sends a control signal of increasing the control word to the variable resistance module, so that the variable resistance module reduces the loop current to the breakdown current corresponding to the reference voltage output by the electrical stability tester by increasing the variable electronic load resistance.

[0020] In an optional embodiment of the present application, the relationship between the variable electronic load resistance and the control word is expressed as follows: in, is a variable electronic load resistor; is the control word; N is the number of bits of resolution of the controller module.

[0021] An embodiment of the present invention provides a method for calibrating the breakdown current of an electrical stability tester, which is applied to the calibration circuit of the breakdown current of the electrical stability tester. The calibration method includes: adjusting the loop current of a closed loop formed by a variable resistance module and a current measurement module by changing the size of a variable resistance until the electrical stability tester alarms; recording the instantaneous current at the moment of the electrical stability tester alarm, and using the instantaneous current as the breakdown current of the electrical stability tester; and calibrating the breakdown current of the electrical stability tester by adjusting the variable electronic load resistance in the variable resistance module according to the loop current and the breakdown current.

[0022] In an optional embodiment of the present application, the calibration of the breakdown current of the electrical stability tester by adjusting the variable electronic load resistance in the variable resistance module includes: when the loop current is less than the breakdown current corresponding to the output reference voltage of the electrical stability tester, a control signal for reducing the control word is issued so as to increase the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by reducing the variable electronic load resistance.

[0023] In an optional embodiment of the present application, the calibration of the breakdown current of the electrical stability tester by adjusting the variable electronic load resistance in the variable resistance module includes: when the loop current is greater than the breakdown current corresponding to the output reference voltage of the electrical stability tester, a control signal for increasing the control word is issued so as to reduce the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by increasing the variable electronic load resistance.

[0024] In an optional embodiment of the present application, the relationship between the variable electronic load resistance and the control word is expressed as follows: in, is a variable electronic load resistor; is the control word; N is the number of bits of resolution of the controller module; is the first voltage-dividing resistor; is the second voltage-dividing resistor; Sampling resistor.

[0025] like Figure 1 and Figure 2 As shown, the entire circuit consists of a current measurement module (also called an ammeter), a variable resistance module (also called an AC electronic load, a variable load module), and a controller module (also called a controller).

[0026] The current measurement module consists of a current detection resistor , operational amplifier A2, true effective value conversion circuit, and analog-to-digital conversion circuit ADC.

[0027] The controller module can be a microcontroller or ARM or FPGA.

[0028] The variable resistor module consists of the following parts: transformer T, two diodes D1 and D2, voltage divider resistor and , operational amplifier A1, MOS tube, digital-to-analog conversion circuit DAC, sampling resistor composition.

[0029] Furthermore, the output terminal of the tester is connected to the pin 1 of the primary terminal of the transformer T, and the pin 2 of the primary terminal of the transformer T is connected to the current detection resistor One end of The other end is returned to the output of the tester; the non-inverting end of operational amplifier A2 is connected to the current detection resistor The inverting terminal of operational amplifier A2 is connected to the 2nd pin of the primary terminal of transformer T. At the other end, the output end of the operational amplifier A2 is connected to the input end of the true effective value conversion circuit, the output end of the true effective value circuit is connected to the input end of the analog-to-digital conversion circuit ADC, and the digital output end of the ADC is connected to the controller.

[0030] The secondary terminal 3 pin of transformer T is connected to the positive electrode of diode D1, the secondary terminal 5 pin of transformer T is connected to the positive electrode of diode D2, the secondary terminal 4 pin of transformer T is grounded, the cathode of diode D1 is connected to the cathode of diode D2 and connected to the voltage divider resistor One end and the drain of the MOS tube, the voltage divider resistor The other end is connected to the non-inverting terminal of operational amplifier A1 and the voltage divider resistor One end of the voltage divider resistor The other end is grounded, the output end of the operational amplifier A1 is connected to the gate of the MOS tube, and the source of the MOS tube is connected to the input reference voltage end of the digital-to-analog conversion circuit DAC and the sampling resistor One end of the sampling resistor The other end of is grounded, the control signal end of the digital-to-analog conversion circuit DAC is connected to the controller module output, and the output of the digital-to-analog conversion circuit DAC is connected to the inverting end of the operational amplifier A1.

[0031] The core of the entire circuit is to use an isolation transformer to electrically isolate the high-voltage circuit from the programmable variable electronic load implemented by the microcontroller, and to accurately measure the high-voltage loop current through the current measurement module to feedback and adjust the variable load; at the same time, the application of the signal partition module also reduces the electrical interference of the entire circuit and ensures the stability and reliability of the variable resistance module. Analysis of the working principle of variable resistor module: Figure 2 In the circuit, transformer T and diodes D1 and D2 form a full-wave rectifier circuit. The signal is always positive. The advantage of this design is that the high voltage at the primary end is converted into a small voltage at the secondary end, and according to the law of energy conservation, the small current at the primary end is converted into a large current at the secondary end. This provides a basis for the design of variable resistor modules.

[0032] For op amp A1, based on the virtual short of the operational amplifier: (1) because for and The pressure comes from the division, so there are: (2) Since the reference voltage input terminal of the DAC is connected to the sampling resistor The high-side connection, therefore the DAC output voltage for: (3) (Where N is the number of bits of DAC resolution, D is the DAC control word, is the current flowing through the sampling resistor Current) Substituting equation (2) and equation (3) into equation (1), we get: (4) Can launch: (5) From formula (5), we can see that for The equivalent resistance of the branch can be regarded as: (6) From formula (6), we can see that Branch equivalent resistance It can be adjusted by DAC control word D. Changing D can change size.

[0033] right The resistance of the branch is: (7) For the entire For the circuit, its equivalent load is: (8) Because when designing the circuit, and The resistor design value is very large, so it leads to >> ,at this time: (9) From formula (9), we can see that the equivalent resistance of the entire circuit is Adjusted by the DAC control word D, the equivalent resistance of the entire loop can be changed by changing D through the controller MCU size.

[0034] The current measurement module is mainly composed of a current detection resistor , differential amplifier A2, true RMS conversion current and ADC. It is an AC current, so it is necessary to accurately measure the current flowing through the current detection resistor through the operational amplifier A2. The voltage at both ends is converted into an effective value and finally enters the ADC to accurately measure the breakdown current. size.

[0035] Furthermore, the differential operational amplifier A2 measures the voltage between the same-direction input terminal and the reverse input terminal of the operational amplifier A2, so the output terminal of A2 is the voltage across Rz. The effective value conversion circuit is a circuit that converts an AC signal into an effective value signal. This circuit can be realized by a special chip, such as AD637. ADC is a chip that converts analog signals into digital signals. Here, it is equivalent to ADC measuring the effective value of the voltage across Rz. According to Ohm's law, current is equal to voltage divided by resistance Rz, and the current I0 can be obtained.

[0036] The loop current refers to the current in the entire loop; and the breakdown current refers to the loop current threshold of 61μA set inside the electrical stability tester. When the loop current is greater than this value, the electrical stability tester automatically cuts off the voltage output and sends out an alarm signal. The present invention is to accurately measure the current at the time when the point stability tester sends out an alarm signal. The current at this time is the breakdown current.

[0037] Overall working principle: When the entire circuit is working, it can be seen from formula (9) that when the loop current When the breakdown current is less than the breakdown current of the electrical stability tester, the MCU output control word D decreases and the variable electronic load resistance Reduced, making the loop current Increase; on the contrary, when the loop current When the breakdown current is greater than the breakdown current of the electrical stability tester, the MCU output control word D increases, and the variable electronic load resistance Increases, making the loop current The design of the entire circuit module eliminates the need to manually select high and low voltage resistors or the output voltage of the electrical stability tester being tested, overcomes the large uncertainty caused by the use of physical resistors and peak current meters, improves calibration efficiency, and ensures the accuracy of the tester breakdown current calibration.

[0038] MCU has IO control pins as well as SPI bus, I2C bus, etc. DAC is a chip that converts digital signals into analog signals. MCU can control DAC through IO or bus, which is the control word that controls DAC.

[0039] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the present invention is not limited thereby. Any modification, equivalent substitution and improvement made by those skilled in the art without departing from the scope and essence of the present invention shall be within the scope of the present invention.

Claims

1. A calibration circuit for breakdown current of an electrical stability tester, characterized in that: It includes a current measurement module, a controller module and a variable resistance module; The first input end of the variable resistance module is connected to the electric stability tester, the second input end is connected to the controller module, and the output end is connected to the current measurement module; The first input end of the current measurement module is connected to the electrical stability tester, the second input end is connected to the variable resistance module, and the output end is connected to the controller module, and is used to measure the loop current of the closed loop formed by the variable resistance module and the current measurement module, and output the measured loop current to the controller module; The controller module is used to send a control signal to the variable resistor module according to the loop current and the breakdown current corresponding to the reference voltage output by the electrical stability tester, thereby changing the resistance of the variable resistor module until the electrical stability tester alarms for breakdown.

2. The calibration circuit according to claim 1, characterized in that: The current measurement module consists of a current detection resistor , differential operational amplifier A2, true effective value conversion circuit and analog-to-digital conversion circuit ADC; Current Sense Resistor One end of the current detection resistor is connected to the 2nd foot of the primary end of the transformer T in the variable resistor module. The other end is returned to the output of the tester, and the non-inverting end of the operational amplifier A2 is connected to the current sensing resistor The inverting terminal of operational amplifier A2 is connected to the 2nd pin of the primary terminal of transformer T. At the other end, the output end of the operational amplifier A2 is connected to the input end of the true effective value conversion circuit, the output end of the true effective value circuit is connected to the input end of the analog-to-digital conversion circuit ADC, and the digital output end of the ADC is interconnected with the controller module.

3. The calibration circuit according to claim 2, characterized in that: The controller module is a single chip microcomputer or an ARM or an FPGA.

4. The calibration circuit according to claim 3, characterized in that: The variable resistance module is composed of a transformer T, a first diode D1, a second diode D2, a first voltage dividing resistor , the second voltage divider resistor , operational amplifier A1, MOS tube, digital-to-analog conversion circuit DAC and sampling resistor composition; The primary end 1 pin of the transformer T is connected to the output end of the electrical stability tester, the secondary end 3 pin of the transformer T is connected to the positive electrode of the first diode D1, the secondary end 5 pin of the transformer T is connected to the positive electrode of the second diode D2, the secondary end 4 pin of the transformer T is grounded, the cathode of the first diode D1 is connected to the cathode of the second diode D2 and connected to the first voltage divider resistor One end and the drain of the MOS tube, the first voltage divider resistor The other end is connected to the non-inverting terminal of operational amplifier A1 and the second voltage divider resistor One end of the second voltage divider resistor The other end is grounded, the output end of the operational amplifier A1 is connected to the gate of the MOS tube, and the source of the MOS tube is connected to the input reference voltage end of the digital-to-analog conversion circuit DAC and the sampling resistor One end of the sampling resistor The other end of is grounded, the control signal end of the digital-to-analog conversion circuit DAC is connected to the controller module output, and the output end of the digital-to-analog conversion circuit DAC is connected to the inverting end of the operational amplifier A1.

5. The calibration circuit according to claim 4, characterized in that: The output end of the controller module sends a control signal to the variable resistor module according to the loop current and the breakdown current corresponding to the reference voltage output by the electrical stability tester, including: When the loop current is less than the breakdown current corresponding to the output reference voltage of the electrical stability tester, the controller module sends a control signal for reducing the control word to the variable resistance module, so that the variable resistance module increases the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by reducing the variable electronic load resistance; When the loop current is greater than the breakdown current corresponding to the output reference voltage of the electrical stability tester, the controller module sends a control signal to increase the control word to the variable resistance module, so that the variable resistance module increases the variable electronic load resistance to reduce the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester.

6. The calibration circuit according to claim 5, characterized in that: The relationship between the variable electronic load resistance and the control word is expressed as: in, is a variable electronic load resistor; is the control word; N is the number of bits of resolution of the controller module.

7. A method for calibrating the breakdown current of an electrical stability tester, characterized in that: The calibration circuit for the breakdown current of the electrical stability tester according to any one of claims 1 to 6, wherein the calibration method comprises: By changing the size of the variable resistor, the loop current of the closed loop formed by the variable resistor module and the current measurement module is adjusted until the electrical stability tester alarms; Recording the instantaneous current at the moment when the electrical stability tester gives an alarm, and using the instantaneous current as the breakdown current of the electrical stability tester; According to the loop current and the breakdown current, the breakdown current of the electrical stability tester is calibrated by adjusting the variable electronic load resistance in the variable resistance module.

8. The calibration method according to claim 7, characterized in that: The method of calibrating the breakdown current of the electrical stability tester by adjusting the variable electronic load resistance in the variable resistance module includes: When the loop current is less than the breakdown current corresponding to the output reference voltage of the electrical stability tester, a control signal for reducing the control word is issued so as to increase the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by reducing the variable electronic load resistance.

9. The calibration method according to claim 7, characterized in that: The method of calibrating the breakdown current of the electrical stability tester by adjusting the variable electronic load resistance in the variable resistance module includes: When the loop current is greater than the breakdown current corresponding to the output reference voltage of the electrical stability tester, a control signal for increasing the control word is issued so as to reduce the loop current to the breakdown current corresponding to the output reference voltage of the electrical stability tester by increasing the variable electronic load resistance.

10. The calibration method according to claim 8 or 9, characterized in that: The relationship between the variable electronic load resistance and the control word is expressed as: in, is a variable electronic load resistor; is the control word; N is the number of bits of resolution of the controller module; is the first voltage-dividing resistor; is the second voltage-dividing resistor; Sampling resistor.

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