Method and device for measuring and correcting load effect of sampling resistor under low air pressure

Abstract

The invention discloses a method and a device for measuring and correcting the load effect of a sampling resistor under low air pressure. According to the invention, air pressure parameters are introduced into a measurement task of a sampling resistor load effect, and an error function model R (T, P, A) based on temperature T, air pressure A, load power P and a sampling resistance value R is established, so that the limitation that measurement cannot be carried out under low air pressure in a traditional measurement method is solved; a temperature coefficient, a load coefficient and an air pressure coefficient are accurately measured through the low-air-pressure sampling resistor load effect measuring device, and the problem of the sampling resistor load effect under the low air pressure can be effectively quantified. According to the method for measuring and correcting the load effect of the sampling resistor under the low air pressure, the resistance value under the actual working condition can be accurately measured, meanwhile, the real resistance value under any working condition can be deduced according to the error correction model R (T, P and A), the current measurement error is further corrected, and the accuracy of current measurement is improved.

Description

Technical Field

[0001] The invention belongs to the field of precision electrical measurement, and in particular relates to a method and device for measuring and correcting the load effect of a sampling resistor under low pressure. Background Art

[0002] In aerospace applications, in order to monitor the working performance of solar cells on aircraft, it is necessary to accurately measure their output current. Precision resistors are often used to measure current, which are called sampling resistors. The current produces a voltage drop on the sampling resistor, and Ohm's law is used to obtain the measured current value. When current flows through the sampling resistor, the current generates work and heat, causing the resistor temperature to rise. This phenomenon that causes the resistance value to change is called the load effect of the sampling resistor, which is specifically characterized by the load coefficient. Accurately measuring the sampling resistor load coefficient can effectively quantify the resistance value error caused by the load effect, thereby correcting the resistance value and ensuring the accuracy of current measurement.

[0003] At present, in order to solve the problem of resistor load effect, one method is to reduce the thermal resistance of the resistor to the surrounding environment to improve the influence of the load effect. The China Institute of Metrology has developed an "extremely low load effect distributed sampling resistor" and increased the contact area between multiple internal small resistor elements and the outside world to reduce thermal resistance. This method complicates the internal structure of the resistor, increases the volume, and is difficult to be applied in actual circuits; another method is to derive the thermal resistance calculation formula based on the zero load effect point, obtain the manganese copper wire resistor thermal resistance measurement method, and further obtain the actual temperature rise of the resistor. This method is limited to resistors with zero load effect points, is not widely applicable to most resistors, and cannot accurately describe the resistance value error caused by the load effect.

[0004] In terms of load effect measurement, the combination of a precision voltage divider and a potentiometer is used to change the load power of the resistor within a sufficiently wide range and accurately measure the load effect of the resistor. In order to achieve automated measurement, a resistor load factor test system based on a DC current comparator (DCC) has been designed, and the load factor calibration calculation method and uncertainty transfer law have been derived. However, the existing technology aims to improve the measurement method or increase the measurement accuracy, and no research on load effect correction has been carried out, and the test conditions are all constant temperature and pressure.

[0005] As the altitude of the spacecraft increases, the ambient temperature affects the thermal characteristics of the resistor, and it is usually placed in a constant temperature device to offset the influence of the external temperature. The change in air pressure will, on the one hand, cause the sealing structure of the resistor to undergo mechanical deformation and change the physical properties of the resistor wire; on the other hand, the change in the heat transfer form of the resistor under low air pressure will cause its heat dissipation capacity to decrease. Therefore, the previous measurement method under normal pressure cannot accurately describe the load effect of the sampling resistor working under low air pressure.

[0006] In summary, the existing load effect measurement methods and test systems are not suitable for the study of resistor load effect under low pressure, and it is difficult to further correct the resistor load effect. Therefore, it is urgent to propose a new method for measuring and correcting the sampling resistor load effect under low pressure to accurately measure the resistor error and improve the current measurement accuracy. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a method and device for measuring and correcting the load effect of a sampling resistor under low pressure.

[0008] The technical solution adopted by the present invention to solve the technical problem is:

[0009] In a first aspect, the present invention provides a method for measuring and correcting a sampling resistor load effect under low pressure, the method comprising:

[0010] The temperature characteristic curve of the sampling resistor is obtained to obtain the temperature coefficient α of the first term and the temperature coefficient β of the second term, and the reference temperature point T0 of the load effect test and the sampling resistor value R0 at the reference temperature point T0 are determined.

[0011] The load effect curve of the sampling resistor under low pressure is obtained, the first-order load coefficient η and the second-order load coefficient γ under different test pressures are obtained, and the functional relationship between η, γ and the air pressure A is established.

[0012] The air pressure characteristic curve of the sampling resistor is obtained, the air pressure coefficient μ is obtained, and a functional relationship between the air pressure A and the resistance value R under zero load power is established.

[0013] The temperature characteristics of the sampling resistor, the load effect under low pressure, and the air pressure characteristics are measured, and an error correction function R(T, P, A) based on the temperature T, the air pressure A, the load power P, and the sampling resistance value R is established. The linear temperature coefficient α, the quadratic temperature coefficient β, the linear load coefficient η, the quadratic load coefficient γ, and the air pressure coefficient μ are input into the error correction function R(T, P, A) to obtain the sampling resistor correction value R*.

[0014] Design a current measurement circuit and current correction scheme to correct the measured current I based on the sampling resistance correction value R*.

[0015] In some preferred embodiments, the calculation formulas for the linear temperature coefficient α and the quadratic temperature coefficient β are:

[0016] R=R0[1+α(T-T0)+β(T-T0) 2 ]

[0017] Wherein, R0 is the resistance value at the reference temperature T0, and R is the resistance value at the current temperature T.

[0018] In some preferred embodiments, the calculation formulas for the linear load coefficient η and the quadratic load coefficient γ are:

[0019] R=R0[1+η(P-P0)+γ(P-P0) 2 ]

[0020] Among them, P0 is the zero load power and R is the resistance value when the current load power P is.

[0021] Under load, the effect of air pressure on the heat dissipation of the resistor can be expressed as a function of the load factor and air pressure:

[0022] η=a1+a2A+a3A 2 +…+a n A n-1

[0023] γ=b1+b2A+b3A 2 +…+b n A n-1

[0024] Among them, a, b and n are constants, and A is the current air pressure.

[0025] In some preferred embodiments, the calculation formula of the air pressure coefficient μ is:

[0026] R=R0[1+μ(A-A0)]

[0027] Among them, A0 is the standard atmospheric pressure and R is the resistance value at the current air pressure A.

[0028] In some preferred embodiments, the construction of the sampling resistance error correction function R (T, P, A) includes:

[0029] The temperature characteristics of the sampling resistor, the load effect under low pressure, and the pressure characteristics are linearly superimposed to establish an error correction function R(T, P, A) based on temperature T, pressure A, load power P, and sampling resistor value R. The calculation formula is as follows:

[0030] R(T,P,A)=R0+R0[α(T-T0)+β(T-T0) 2 ]+R0[η(P-P0)+γ(P-P0) 2 ]+μR0(A-A0)

[0031] In some preferred embodiments, the current measurement circuit comprises:

[0032] Current measurement module, AD acquisition module and MCU main control module.

[0033] The current measurement module is used to convert the voltage across the sampling resistor into a voltage signal that can be collected.

[0034] The AD acquisition module is used to acquire the voltage signal output by the current measurement module.

[0035] The MCU main control module is used to communicate with the AD acquisition module to obtain the voltage signal U output by the AD acquisition module; and is used to receive and control the current temperature T, air pressure A and load power P;

[0036] In some preferred embodiments, the current correction scheme includes:

[0037] Calculation unit and correction unit.

[0038] The calculation unit is used to substitute the current temperature T, air pressure A and load power P acquired by the MCU main control module into the error correction function R(T, P, A), and calculate the sampling resistance correction value R* in real time.

[0039] The correction unit is used to divide the sampling resistance correction value R* by the voltage value U output by the AD acquisition module to calculate the current correction value I*.

[0040] In a second aspect, the present invention also provides a device for measuring a sampling resistor load effect under low pressure, the device comprising:

[0041] The electric measuring unit includes a high-precision digital multimeter and a high-precision current source, which are used to obtain the sampling resistance value R, the voltage value U across the sampling resistance, and provide the measured current value I.

[0042] The air pressure control unit includes a vacuum pump, a solenoid valve, an air pressure sensor, an air pressure tank, and a vacuum box, and is used to generate low-pressure test conditions.

[0043] The temperature control unit is used to achieve temperature balance inside and outside the vacuum box. The external temperature control module includes a constant temperature box and a temperature controller; the internal temperature control module includes a heating wire and a temperature sensor.

[0044] The driving unit includes a power supply module and a driving circuit, and is used to drive the devices of the air pressure control unit and the temperature control unit to operate at a required voltage.

[0045] The main control unit includes a lower computer MCU main control module and a host computer test software. The MCU main control module is used for data transmission and control instruction transmission of the air pressure control unit and the temperature control unit. The host computer test software includes a computer and a measurement software, which is used to display and save the data uploaded by the lower computer MCU main control module and to send execution instructions.

[0046] The present invention adopts the above technical solution, and has the following characteristics:

[0047] 1. The present invention introduces air pressure parameters into the measurement task of the sampling resistor load effect, and establishes an error function model R (T, P, A) based on temperature T, air pressure A, load power P and sampling resistor value R, which solves the limitation that traditional measurement methods cannot measure under low air pressure, and accurately measures the temperature coefficient, load coefficient and air pressure coefficient through a low-pressure sampling resistor load effect measurement device, which can effectively quantify the sampling resistor load effect problem under low air pressure.

[0048] 2. The method for measuring and correcting the load effect of a sampling resistor under low pressure provided by the present invention can not only accurately measure the resistance value under actual working conditions, but also derive the true value of the resistance under any working conditions based on the error correction model R (T, P, A), and further correct the current measurement error, thereby improving the accuracy of the current measurement.

[0049] In summary, the present invention provides a feasible solution for measuring and correcting the sampling resistor load effect under low pressure, and also lays a solid foundation for current measurement technology under low pressure, solves the limitations of current measurement technology, and can be widely used in the field of electrical measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings:

[0051] Figure 1 The present invention is a flowchart of a method for measuring and correcting a sampling resistor load effect under low pressure according to some embodiments of the present invention.

[0052] Figure 2 This is a block diagram of a sampling resistor temperature characteristic test experiment according to some embodiments of the present invention.

[0053] Figure 3 1 is a temperature characteristic curve of a sampling resistor according to some embodiments of the present invention.

[0054] Figure 4 This is a block diagram of a test experiment for sampling resistor load effect under low pressure in some embodiments of the present invention.

[0055] Figure 5 FIG. 4 is a block diagram of an air pressure control system according to some embodiments of the present invention.

[0056] Figure 6 FIG. 4 is a block diagram of a temperature control system according to some embodiments of the present invention.

[0057] Figure 7 1 is a curve of the sampling resistor load effect under low pressure according to some embodiments of the present invention.

[0058] Figure 8 1 is a curve of load factor and air pressure according to some embodiments of the present invention.

[0059] Fig. 9 1 is a sampling resistor pressure characteristic curve of some embodiments of the present invention.

[0060] Fig.10 This is a sampling resistor error correction model for some embodiments of the present invention.

[0061] Fig.11 A block diagram of sampling resistance correction and current measurement correction according to some embodiments of the present invention.

[0062] Fig.12 Schematic diagram of comparing the current measurement accuracy before and after correction in some embodiments of the present invention. DETAILED DESCRIPTION

[0063] It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive, and therefore specify the existence of stated features, steps, operations, elements and / or parts, but do not exclude the existence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not interpreted as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0064] Although the terms first, second, third, etc. can be used in the text to describe multiple elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section without departing from the teaching of the example embodiments.

[0065] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside", "outside", "inner side", "outer side", "below", "above", etc. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0066] In view of the limitations of the existing sampling resistor load effect measurement method, the present invention introduces air pressure parameters and improves the measurement method. The present invention provides a method for measuring and correcting the load effect of a sampling resistor under low pressure, including: obtaining a temperature characteristic curve of the sampling resistor, obtaining temperature coefficients α and β, and determining the sampling resistance value R0 at reference temperature points T0 and T0; obtaining the load effect curve of the sampling resistor under low pressure, obtaining load coefficients η and γ, and establishing a functional relationship between η, γ and air pressure; obtaining the air pressure characteristic curve of the sampling resistor under zero load power, obtaining the air pressure coefficient μ; establishing an error correction function R(T, P, A) based on temperature T, air pressure A, load power P and resistance value R; completing the measurement of the sampling resistor load effect under low pressure, inputting the first-order temperature coefficient α, the second-order temperature coefficient β, the first-order load coefficient η, the second-order load coefficient γ, and the air pressure coefficient μ into the error correction function R(T, P, A), and obtaining the sampling resistor correction value R*; designing a current measurement circuit and a current correction scheme, and obtaining the current correction value I* based on the sampling resistor correction value R*. Therefore, the present invention provides a new and efficient solution for measuring and correcting the sampling resistor load effect under low pressure (10-100 kPa) by establishing an R (T, P, A) error correction model.

[0067] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0068] Embodiment 1: Figure 1 As shown, this embodiment provides a method for measuring and correcting the load effect of a sampling resistor under low pressure, including:

[0069] The temperature characteristic curve of the sampling resistor is obtained, and the temperature coefficient α of the first term and the temperature coefficient β of the second term are obtained. The reference temperature point T0 of the load effect test and the resistance value R0 at the reference temperature point T0 are determined.

[0070] In this embodiment, according to the existing GB / T 6148-2005 "Test Method for Temperature Coefficient of Resistance of Precision Resistance Alloys", the resistance value corresponding to the experimental temperature point is measured, and the resistance-temperature characteristic curve within the experimental temperature range is fitted.

[0071] In this embodiment, the sampling resistance value R can be measured by using the high-precision digital multimeter Agilent 34420A resistance range to ensure that the resistance value change of 0.001% can be measured, and the upper computer measurement software is connected to measure multiple times to take the average value after the resistance is stable. The ambient temperature T of the sampling resistor is controlled by a constant temperature box and a temperature controller, and the temperature stability is ±0.2°C. The resistance temperature characteristic curve is fitted by the least squares method.

[0072] Furthermore, in this embodiment, the temperature coefficients α and β are determined by the resistance temperature characteristic curve formula, such as the following formula, at the reference temperature T0 by the first-order term and the second-order term coefficient.

[0073] R=R0[1+α(T-T0)+β(T-T0) 2 ]

[0074] Among them, R0 is the resistance value at the reference temperature point T0, T is the current temperature, α and β are the temperature coefficients of the first and second terms.

[0075] Furthermore, the extreme point of the sampling resistor temperature characteristic formula is obtained, which is the zero temperature coefficient point of the resistance, with the horizontal axis as the reference temperature T0 and the vertical axis as the sampling resistance value R0 at the reference temperature T0.

[0076] The load effect curve of the sampling resistor under low pressure is obtained, the first-order load coefficient η and the second-order load coefficient γ under different test pressures are obtained, and the functional relationship between η, γ and the air pressure A is established.

[0077] In this embodiment, the air pressure A is adjusted at the reference temperature point T0, the resistance value R corresponding to the load power point at each air pressure point is measured, and the sampling resistor load effect curves at different air pressures are fitted respectively.

[0078] In this embodiment, the high-precision power supply DP2031 constant current mode can be used to output the load current and control the sampling resistor load power P; the high-precision digital multimeter Agilent 3458A current range is used to measure the actual output current I, and the Agilent 34420A voltage range is used to measure the voltage U across the sampling resistor, and the stabilized sampling resistor value R is calculated according to Ohm's law; the air pressure control unit is used to adjust the ambient air pressure A of the sampling resistor, and the air pressure stability is 50Pa / min; the external temperature T1 of the vacuum box is adjusted by a constant temperature box and a temperature controller, and the internal temperature T2 of the vacuum box is adjusted by a temperature control unit, and the temperature stability is ±0.2°C, so as to achieve the temperature balance T1=T2 inside and outside the vacuum box, and the least squares method is used to fit the resistor load effect curve at each air pressure point.

[0079] Furthermore, in this embodiment, the load coefficients η and γ are determined by the first-order and second-order coefficients of the resistance load effect curve formula, such as the following formula.

[0080] R=R0[1+η(P-P0)+γ(P-P0) 2 ]

[0081] Wherein, R0 is the resistance value at the reference temperature point T0, P is the current power, P0 is the zero load power, η and γ are the first-order and second-order load coefficients.

[0082] Furthermore, the first-order load coefficient η and the second-order load coefficient γ are functions related to the air pressure A, respectively. The η(A) and γ(A) curves are obtained by fitting using the least squares method. The functional relationship between the load coefficients η and γ and the air pressure A is as follows:

[0083] η=a1+a2A+a3A 2 +…+a n A n-1

[0084] γ=b1+b2A+b3A 2 +…+b n A n-1

[0085] Among them, a, b and n are constants, and A is the current air pressure.

[0086] The air pressure characteristic curve of the sampling resistor is obtained, the air pressure coefficient μ is obtained, and a functional relationship between the air pressure A and the resistance value R under zero load power P0 is established.

[0087] In this embodiment, the high-precision digital multimeter Agilent 34420A resistance range can be used to measure the sampling resistance value R, connect to the host computer measurement software, measure multiple times, and take the average value after the resistance stabilizes. The ambient temperature T of the resistor is controlled to be constant by a constant temperature box and a temperature controller, and the temperature stability is ±0.2°C. The ambient air pressure A of the sampling resistor is adjusted by a pressure control unit, and the air pressure stability is 50Pa / min; the resistance-air pressure characteristic curve within the experimental air pressure range is fitted by the least squares method.

[0088] Furthermore, in this embodiment, the pressure coefficient μ is determined by the first-order coefficient of the resistance-pressure characteristic curve formula at the reference temperature T0 and the zero load power P0.

[0089] R=R0[1+μ(A-A0)]

[0090] Among them, R0 is the resistance value at the reference temperature point T0 and zero load power P0, A0 is the standard atmospheric pressure, and A is the current air pressure.

[0091] In this embodiment, the linear temperature coefficient α, the quadratic temperature coefficient β, the linear load coefficient η, the quadratic load coefficient γ, and the air pressure coefficient μ are input into the error correction function R(T, P, A), and an error correction function R(T, P, A) based on temperature T, air pressure A, load power P and resistance value R is established. The calculation formula is as follows:

[0092] R(T,P,A)=R0+R0[α(T-T0)+β(T-T0) 2 ]+R0[η(P-P0)+γ(P-P0) 2 ]+μR0(A-A0)

[0093] Among them, T is the current temperature, T0 is the reference temperature, P is the current load power, P0 is the zero load power, A is the current air pressure, and A0 is the standard atmospheric pressure.

[0094] Furthermore, the error correction function R(T, P, A) is used to establish a three-dimensional resistance error correction model R(P, A) using Matlab mathematical software at a fixed temperature point T. By changing the temperature T, resistance error correction models at different temperature points can be established.

[0095] Design a current measurement circuit and current correction scheme to correct the measured current based on the sampling resistance correction value.

[0096] In this embodiment, the current measurement circuit includes: a current measurement module, an AD acquisition module, and an MCU main control module. The current measurement module is used to convert the voltage across the sampling resistor into a voltage signal that can be collected. The AD acquisition module is used to collect the voltage signal output by the current measurement module. The MCU main control module is used to communicate with the AD acquisition module to obtain the voltage signal output by the AD acquisition module, and is used to receive and control the current temperature, air pressure and load power;

[0097] Furthermore, the current end of the sampling resistor is connected in series in the load circuit, and the voltage end is connected to the current measurement module. The current measurement module measures the voltage U0 across the sampling resistor, and amplifies it to a voltage value U that can be collected according to the set gain through the current measurement circuit as output.

[0098] Furthermore, the AD acquisition module receives the voltage value U and converts it into a digital value Value as output through A / D.

[0099] Furthermore, the MCU main control module receives the AD digital value Value and converts it into an analog voltage value U. The conversion formula is as follows:

[0100]

[0101] Among them, Value is the AD digital value, Bit is the maximum value of the AD chip digital output, and Range is the voltage range of the AD acquisition module.

[0102] In this embodiment, the current correction scheme includes: a calculation unit and a correction unit. The calculation unit is used to calculate the current temperature, air pressure and load power values ​​obtained by the MCU main control module in real time to obtain the sampling resistance correction value R*. The correction unit is used to divide the sampling resistance correction value R* by the voltage value U output by the AD acquisition module to obtain the current measurement correction value I*.

[0103] Furthermore, the MCU main control module obtains the current temperature T, air pressure A and load power P, and uses the error correction function R(T, P, A) stored in the Flash to obtain the sampling resistance correction value R*.

[0104] Furthermore, the MCU main control module calculates the current correction value I* by adding the voltage analog quantity U and the sampling resistance correction value R* according to Ohm's law. The calculation formula is as follows:

[0105]

[0106] Through the above embodiments, the measurement and correction of the sampling resistor load effect under low pressure are achieved.

[0107] The following describes in detail a method for measuring and correcting a sampling resistor load effect under low pressure according to the present invention through specific embodiments.

[0108] 1. In the sampling resistor temperature characteristic test phase, the temperature characteristic curve is obtained to obtain the first-order temperature coefficient α and the second-order temperature coefficient β, and the sampling resistor value R0 at the reference temperature points T0 and T0 is determined.

[0109] In this embodiment, the test resistor is a four-terminal lead RX76 type wire wound manganese copper wire sampling resistor with a resistance of 1Ω, a rated power of 2W, and an accuracy of ±0.1%. According to the existing GB / T 6148-2005 "Test Method for Temperature Coefficient of Resistance of Precision Resistor Alloys", the temperature characteristics of the sampling resistor are measured.

[0110] In this embodiment, Figure 2 As shown, the low-power four-wire resistance measurement mode of Agilent 34420A is used to measure the sampling resistor, and the measurement accuracy reaches 0.001%. The test probe maintains good electrical contact with the four terminals of the sampling resistor. At the same time, the current test probe is clamped on the outside of the voltage test probe to reduce the lead resistance. The 34420A is turned on and preheated for 4 hours, and the acquisition cycle is set to 6.3s. The ambient temperature of the constant temperature box is controlled by a temperature controller, and the temperature fluctuation is ≤±0.2℃. The sampling resistor is hung in the center of the constant temperature box and the temperature is averaged for 30 minutes.

[0111] Furthermore, in the experimental temperature range of 15°C to 35°C, a step-temperature rising method was adopted. After each temperature point was stabilized for 30 minutes, the resistance value was measured 500 times by the host computer. The average value of the last 200 values ​​was taken as the resistance value of the temperature point, and 21 temperature points were measured continuously.

[0112] Furthermore, the least square method is used to fit the temperature characteristic curves of 21 temperature points and the corresponding resistance average values ​​of the 21 temperature points, such as Figure 3 As shown, the linear temperature coefficient α and the quadratic temperature coefficient β are obtained, and the temperature characteristic curve formula is as follows:

[0113] y=0.99877+4.8851×10 -5 x-6.8551×10 -7 x 2

[0114] Furthermore, the extreme point of the temperature characteristic curve is calculated to obtain the zero temperature coefficient point, which is used as the reference temperature point T0. The resistance value R0 corresponding to the time T0 is obtained. The measured results are R0 = 0.9987701Ω, T0 = 35.7°C, α = 14.6ppm / °C, β = -0.69ppm / °C 2 .

[0115] 2. In the sampling resistor load effect test phase under low pressure, the load effect curves under different pressures are obtained, the first-order load coefficient η and the second-order load coefficient γ are obtained, and the functional relationship between η, γ and the pressure A is established.

[0116] In this embodiment, Figure 4 As shown, the MCU main control module controls the internal air pressure and temperature of the vacuum box, and the temperature controller controls the constant temperature box as the external temperature of the vacuum box; the DP2031 power supply is used to output a constant current with a programming accuracy of 0.15% to control the sampling resistor load power; the Agilent 3458A is used to measure the actual value of the DP2031 output current with an accuracy of 0.01%; and the Agilent 34420A is used to measure the voltage across the sampling resistor.

[0117] Furthermore, the host computer uses USART serial port to connect to the MCU main control module, RS485 serial port to connect to the temperature controller, RS232 serial port to connect to Agilent 34420A, DP2031 and Agilent 3458A, and displays the measured voltage, current, resistance, temperature and air pressure in real time.

[0118] Furthermore, if Figure 5 As shown, the MCU main control module of the temperature control unit obtains the current air pressure inside the vacuum box through the air pressure sensor, compares it with the set air pressure, and determines whether the error signal exceeds the set threshold. If it exceeds the set threshold, the MCU main control module turns on the drive circuit, opens the solenoid valve, and starts the vacuum pump to extract the gas in the vacuum box until the air pressure value is lower than the set threshold.

[0119] In this embodiment, Figure 6 As shown, the MCU main control module of the air pressure control unit obtains the current temperature in the vacuum box through the temperature sensor, compares it with the target temperature, and determines whether the error signal exceeds the set threshold. If it exceeds the set threshold, the MCU main control module converts the error signal into a DAC digital quantity through a fuzzy PID controller, and compares it with the working voltage digital quantity after voltage sampling. The error signal is used as the input signal of dynamic voltage regulation.

[0120] Furthermore, the dynamic voltage regulation module receives the voltage error signal as a feedback input signal of the adjustable power chip in the dynamic voltage regulation module to control the power of the heating wire and achieve temperature regulation.

[0121] In this embodiment, the temperature inside and outside the vacuum box is set to the reference temperature T0, DP2031 is adjusted to the constant current output mode, 3458A is adjusted to the current range, and 34420A is adjusted to the voltage range. The sampling resistor is connected to the vacuum box through an airtight insulated four-core shielded connector and cable, and the test probe maintains good electrical contact with the four terminals of the sampling resistor. At the same time, the current test probe is clamped on the outside of the voltage test probe, and the sampling resistor is suspended in the center of the vacuum box and the temperature is averaged for 30 minutes.

[0122] Furthermore, the sampling resistor load power is set to 0.2W~2W, and the DP2031 output current value is adjusted with a gradient of 0.2W. After the resistor is thermally balanced at each power point, the average value of the last 200 resistance values ​​is taken as the resistance value of the load power point, and 10 load power points are measured continuously.

[0123] Furthermore, the load effect curves of 10 load power points and the average values ​​of the resistances corresponding to the 10 load power points are fitted by the least squares method to obtain the first-order load coefficient η and the second-order load coefficient γ. For example, the load effect formula of the 100kPa sampling resistor is as follows:

[0124] R=1.00627-8.56587×10 -4 x-3.67557×10 -4 x 2

[0125] Furthermore, the first-order load factor η = -856.6ppm / W and the second-order load factor γ = -365.3ppm / W are obtained. 2 .

[0126] Furthermore, the MCU main control module sets the air pressure in the vacuum box to 100 kPa, 80 kPa, 60 kPa, 40 kPa, 20 kPa, and 10 kPa, and performs the above load effect test at 6 air pressure values ​​to obtain the load effect curve of the sampling resistor under low air pressure, as shown in FIG. Figure 7 Calculate the linear load coefficients η1, η2, η3, η4, η5, η6 and the quadratic load coefficients γ1, γ2, γ3, γ4, γ5, γ6 under 6 atmospheric pressures.

[0127] Furthermore, the η(A) and γ(A) curves are obtained by fitting using the least squares method, as shown in Figure 8 As shown, the functional relationship between the load factors η and γ and the air pressure A is as follows:

[0128] η=-0.00143+1.60419×10 -5 A-9.74069×10 -8 A 2

[0129] γ=-5.18199×10 -4 +1.15257×10 -6 A-5.39457×10 -9 A 2

[0130] 3. In the sampling resistor air pressure characteristic test phase, the air pressure characteristic of the sampling resistor under zero load power is obtained, the air pressure coefficient μ is obtained, and a functional relationship between the air pressure A and the resistance value R under zero load power is established.

[0131] In this embodiment, the MCU main control module controls the internal air pressure and temperature of the vacuum box, the temperature controller controls the constant temperature box as the external temperature of the vacuum box, and the 34420A is set to a low-power four-wire resistance measurement mode.

[0132] Furthermore, the four wiring terminals of 34420A are correctly connected to the four-terminal leads of the sampling resistor, and the MCU main control module sets the air pressure in the vacuum box to: 100kPa, 80kPa, 60kPa, 40kPa, 20kPa, and 10kPa.

[0133] Furthermore, within the air pressure range of 10 kPa to 100 kPa, the 34420A was used to measure the sampling resistance value at each air pressure value in turn, and the air pressure characteristic curve of the average resistance value corresponding to the six air pressure points was fitted using the least squares method, as shown in FIG. Fig. 9 As shown, the air pressure coefficient μ is obtained, and the air pressure characteristic formula is as follows:

[0134] y=1.00066-4.06533×10 -10 x

[0135] 4. Sampling Resistor Error Model

[0136] In this embodiment, an error correction function R(T, P, A) is established based on temperature T, air pressure A, load power P and resistance value R, and the linear temperature coefficient α, quadratic temperature coefficient β, linear load coefficient η, quadratic load coefficient γ, and air pressure coefficient μ are input into the error correction function R(T, P, A).

[0137] R(T,P,A)=R0+R0[α(T-T0)+β(T-T0) 2 ]+R0[η(P-P0)+γ(P-P0) 2 ]+μR0(A-A0)

[0138] Using Matlab multivariate linear regression method, a resistance error correction model is established, such as Fig.10 As shown, the sampling resistance correction value R* at the reference temperature T, air pressure A, and load power P is obtained.

[0139] 5. Sampling resistance correction and current measurement correction stage

[0140] In this embodiment, Fig.11 As shown, the current measurement module includes: a load RL, a sampling resistor R, four gain adjustment resistors R1 / R2 / R3 / R4, a differential amplifier U1, a low-pass filter composed of R5 and C1, forming a low-side current measurement circuit.

[0141] Furthermore, the VIN power supply terminal is connected to the load RL, the sampling resistor R is connected in series, and then connected to GND; the gain adjustment resistor value is set to configure the gain multiple of the differential amplifier, and the calculation formula is as follows:

[0142]

[0143] Among them, Vout is the output voltage value of the current measurement module, V1 / V2 is the voltage across the sampling resistor R, and Gain is the gain of the differential amplifier U1. Configuration: R1 = R2 = 1kΩ, R3 = R4 = 5.1kΩ, then the gain of U1 Gain = 5.1.

[0144] In this embodiment, the voltage range of the AD acquisition module is 0V to 6.144V, receives the output value Vout of the current measurement module, and outputs the AD digital value Value.

[0145] In this embodiment, the MCU main control module is connected to the slave AD acquisition module as the host through hardware SPI communication. The MCU main control module receives the digital value Value output by the AD acquisition module and converts it into a voltage analog value U in the range of 0V-6.144V. The calculation formula is as follows:

[0146]

[0147] Furthermore, the MCU main control module obtains the current temperature, air pressure and load power, and uses the error correction function R(T, P, A) stored in the Flash to obtain the sampling resistance correction value R*.

[0148] In this embodiment, the above sampling resistor error model is adopted. Assuming that the current sampling resistor works at the reference temperature point T0=35.7°C, the air pressure A=20kPa, and the load power P=1W, the error correction function R(T, P, A) is substituted to calculate the sampling resistor error value caused by the load effect:

[0149] △R=R*-R0=1.0003846-0.9996403=0.0007443

[0150] The sampling resistance correction value R*=1.0003846.

[0151] Furthermore, the MCU main control module calculates the current correction value I* by using the voltage analog quantity U and the sampling resistance correction value R* according to Ohm's law. The calculation formula is as follows:

[0152]

[0153] Assuming the test current range is 0.4A~1.4A, the corresponding sampling resistor load power is 0.2W~2W, the D current measurement accuracy before and after correction is as follows: Fig.12 Comparing the test currents of 0.4A, 0.6A, 0.8A, 1.0A, 1.2A, and 1.4A before and after correction, the accuracy is improved by an average of 1 order of magnitude, which shows that the measurement and correction of the sampling resistor load effect under low pressure can effectively improve the current measurement accuracy.

[0154] Embodiment 2: Embodiment 1 above provides a method for measuring and correcting the load effect of a sampling resistor under low pressure. Correspondingly, this embodiment provides a device for measuring the load effect of a sampling resistor under low pressure. The device provided in this embodiment can implement the method for measuring the load effect of a sampling resistor under low pressure of Embodiment 1. The device can be implemented by software, hardware, or a combination of software and hardware. For the convenience of description. When describing this embodiment, the functions are divided into various units and described separately. Of course, the functions of each unit can be implemented in the same or more software and / or hardware during implementation. For example, the device may include integrated or separate functional modules or functional units to perform the corresponding steps in each method of Embodiment 1. Since the device of this embodiment is basically similar to the method embodiment, the description process of this embodiment is relatively simple. For relevant matters, please refer to the partial description of Embodiment 1. The embodiment of the device for measuring the load effect of a sampling resistor under low pressure provided by the present invention is only schematic.

[0155] Specifically, the present application also provides a device for measuring a sampling resistor load effect under low pressure, the device comprising:

[0156] The electric measuring unit includes a high-precision digital multimeter and a high-precision current source, which are used to obtain the sampling resistance value R, the voltage value U across the sampling resistance, and provide the measured current I.

[0157] The air pressure control unit includes a vacuum pump, a solenoid valve, an air pressure sensor, an air pressure tank, and a vacuum box, and is used to generate low-pressure test conditions.

[0158] The temperature control unit is used to achieve temperature balance inside and outside the vacuum box. The external temperature control module includes a constant temperature box and a temperature controller; the internal temperature control module includes a heating wire and a temperature sensor.

[0159] The driving unit includes a power supply module and a driving circuit, and is used to drive the devices of the air pressure control unit and the temperature control unit to operate at a required voltage.

[0160] The main control unit includes a lower computer MCU main control module and a host computer test software. The MCU main control module is used for data transmission and control instruction transmission of the air pressure control unit and the temperature control unit. The host computer test software includes a computer and a measurement software, which is used to display and save the data uploaded by the lower computer MCU main control module and to send execution instructions.

[0161] Each embodiment in this specification is described in a progressive manner, and the same and similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In the description of this specification, the description of reference terms "a preferred embodiment", "further", "specifically", "in the present embodiment", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of this specification. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring and correcting the load effect of a sampling resistor under low pressure, characterized in that The method includes: Obtain the temperature characteristic curve of the sampling resistor, obtain the first-order temperature coefficient α and the second-order temperature coefficient β, determine the reference temperature point T0 of the load effect test, and the sampling resistor value R0 at the reference temperature point T0; Obtain the sampling resistor load effect curve under low pressure, obtain the first-order load coefficient η and the second-order load coefficient γ under different test pressures, and establish the functional relationship between η, γ and air pressure A; Obtain the air pressure characteristic curve of the sampling resistor, obtain the air pressure coefficient μ, and establish the functional relationship between the air pressure A and the resistance value R under zero load power; Complete the measurements of the sampling resistor's temperature characteristics, load effect under low pressure, and air pressure characteristics, establish an error correction function R(T, P, A) based on temperature T, air pressure A, load power P, and sampling resistor value R, input the linear temperature coefficient α, quadratic temperature coefficient β, linear load coefficient η, quadratic load coefficient γ, and air pressure coefficient μ into the error correction function R(T, P, A) to obtain the sampling resistor correction value.

2. The method for measuring and correcting the load effect of a sampling resistor under low pressure according to claim 1, characterized in that: The calculation formula for the linear temperature coefficient α and the quadratic temperature coefficient β is: R=R0[1+α(T-T0)+β(T-T0) 2 ] Wherein, R0 is the resistance value at the reference temperature T0, and R is the resistance value at the current temperature T.

3. The method for measuring and correcting the load effect of a sampling resistor under low pressure according to claim 1, characterized in that: The calculation formulas for the linear load factor η and the quadratic load factor γ are as follows: R=R0[1+η(P-P0)+γ(P-P0) 2 ] Among them, P0 is the zero load power and R is the resistance value when the current load power P is.

4. The method for measuring and correcting the load effect of a sampling resistor under low pressure according to claim 1, characterized in that: The calculation formula of air pressure coefficient μ is: R=R0[1+μ(A-A0)] Among them, A0 is the standard atmospheric pressure and R is the resistance value at the current air pressure A.

5. The method for measuring and correcting the load effect of a sampling resistor under low pressure according to claim 1, characterized in that: The construction of the sampling resistor error correction function R(T, P, A) includes: The temperature characteristics of the sampling resistor, the load effect under low pressure, and the pressure characteristics are linearly superimposed to establish an error correction function R(T, P, A) based on temperature T, pressure A, load power P, and sampling resistor value R. The calculation formula is as follows: R(T,P,A)=R0+R0[α(T-T0)+β(T-T0) 2 ]+R0[η(P-P0)+γ(P-P0) 2 ]+μR0(A-A0) Wherein, R0 is the resistance value at the reference temperature T0, R is the resistance value at the current temperature T, P0 is the zero load power, R is the resistance value at the current load power P, A0 is the standard atmospheric pressure, and R is the resistance value at the current air pressure A.

6. The method for measuring and correcting the load effect of a sampling resistor under low pressure according to claim 1, characterized in that: It also includes designing a current measurement circuit and a current correction scheme to correct the measured current based on the corrected sampling resistance value.

7. The method for measuring and correcting the load effect of a sampling resistor under low pressure according to claim 6, characterized in that: The current measurement circuit includes a current measurement module, an AD acquisition module and an MCU main control module; The current measurement module is used to convert the voltage across the sampling resistor into a voltage signal that can be collected; The AD acquisition module is used to collect the voltage signal output by the current measurement module; The MCU main control module is used to communicate with the AD acquisition module to obtain the voltage signal U output by the AD acquisition module; and is used to receive and control the current temperature, air pressure and load power.

8. The method for measuring and correcting the load effect of a sampling resistor under low pressure according to claim 7, characterized in that: The current correction scheme includes: Calculation unit and correction unit; The calculation unit is used to calculate the current temperature, air pressure and load power values ​​obtained by the MCU main control module in real time to obtain the sampling resistance correction value R*; The correction unit is used to divide the sampling resistance correction value R* by the voltage value U output by the AD acquisition module to calculate the current measurement correction value I*.

9. A device for measuring the load effect of a sampling resistor under low pressure, characterized in that The device includes: The electric measuring unit includes a high-precision digital multimeter and a high-precision current source, which are used to obtain the sampling resistance value R, the voltage value U across the sampling resistance, and provide the measured current I; An air pressure control unit, including a vacuum pump, a solenoid valve, an air pressure sensor, an air pressure tank, and a vacuum box, is used to generate low-pressure test conditions; Temperature control unit, used to achieve temperature balance inside and outside the vacuum box; external temperature control module, including constant temperature box and temperature controller; internal temperature control module, including heating wire and temperature sensor; A driving unit, including a power module and a driving circuit, for driving the devices of the air pressure control unit and the temperature control unit to operate at a required voltage; The main control unit includes a lower-computer MCU main control module and a host-computer test software. The MCU main control module is used for receiving and sending data and transmitting control instructions for the air pressure control unit and the temperature control unit. The host-computer test software includes a computer and a measurement software, which is used to display and save the data uploaded by the lower-computer MCU main control module and to send execution instructions.

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