Six-wire system strain test and voltage compensation method

Abstract

The invention relates to the technical field of industrial control, in particular to a six-wire system strain test and voltage compensation method, which comprises a Wheatstone bridge, an ADC (Analog to Digital Converter) excitation voltage acquisition module, an ADC strain acquisition measurement module, a DAC (Digital to Analog Converter) bridge circuit excitation module and an FPGA (Field Programmable Gate Array) module. The Wheatstone bridge is composed of three fixed resistors R1, R2 and R3 and a variable resistor R4, and the R4 is a resistance-type strain gauge; the DAC bridge circuit excitation module is mainly used for providing working voltage VEF for two ends EF of a Wheatstone bridge, and the voltage can be adjusted in real time; the ADC excitation voltage acquisition module is mainly used for acquiring voltages VAC at two ends of a Wheatstone bridge AC in real time, and the voltages VAC are used as input signals of a feedback control unit of the FPGA module; the ADC acquisition strain measurement module is mainly used for measuring BD end voltage VBD, and a measurement result is used for dependent variable calculation; and the FPGA module is mainly used for calculating the dependent variable and calculating the voltage required to be fed back and output by the DAC bridge circuit excitation module according to the data measured by the ADC excitation voltage acquisition module, so that the voltage acquired by the ADC excitation voltage acquisition module is kept stable. On the basis of a traditional Wheatstone bridge, the input voltage of the Wheatstone bridge is kept stable by adding the PID feedback control circuit, and the accuracy and accuracy of strain measurement can be greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of industrial control, and in particular to a six-wire strain testing and voltage compensation method. Background Art

[0002] Long-distance, high-resolution and high-accuracy strain measurement plays a vital role in industrial control and scientific research. In the field of industrial control, this measurement technology can be used to monitor the health of large infrastructure such as oil and gas pipelines, high-speed railways, high-voltage transmission lines and large bridges to ensure the safety and reliability of the structure. In scientific research, high-precision strain measurement is crucial for research in fields such as materials science, biomechanics and structural engineering. It helps to understand the behavior of materials under stress, evaluate the mechanical properties and deformation mechanisms of materials, and monitor the damage and failure process of structures.

[0003] In many application scenarios such as tunnels, mines, deep sea and wind tunnels, the internal impedance of cables, drift and nonlinearity of electronic devices, and interference caused by long-distance transmission bring huge challenges to high-resolution and high-accuracy strain measurement. The longer the distance between the strain measurement element and the signal processing board, the greater the strain measurement error. To this end, we propose a six-wire strain measurement and voltage compensation method. Summary of the invention

[0004] The purpose of the present invention is to provide a six-wire strain measurement and voltage compensation method, which uses a six-wire Wheatstone bridge structure to eliminate the influence of wire resistance on the bridge excitation voltage, and uses a voltage PID feedback control structure to stabilize the bridge excitation voltage, thereby improving the resolution and accuracy of long-distance strain measurement, and solving the problem of limited accuracy and resolution of strain measurement over long distances.

[0005] To achieve the above object, the present invention provides the following technical solution: a six-wire strain measurement and voltage compensation method, comprising the following steps:

[0006] The Wheatstone bridge consists of three fixed resistors R1, R2, R3 and one variable resistor R4. R1 and R3 form one arm of the bridge, and R2 and R4 form the other arm of the bridge. R4 is a resistive strain gauge attached to the measured point. The voltage at the BD end of the Wheatstone bridge is measured by the ADC acquisition strain measurement module to calculate the resistance value of R4. Finally, the strain magnitude of the measured point is calculated by the FPGA module.

[0007] The DAC bridge excitation module provides the operating voltage for the EF ends of the Wheatstone bridge. The voltage is controlled by the FPGA module and can adjust the voltage in real time to maintain the voltage V across the AC ends of the Wheatstone bridge. AC Maintain a set voltage level.

[0008] Preferably, in order to maintain the voltage across the Wheatstone bridge AC stable, there is a feedback control unit inside the FPGA module. The feedback control unit adopts PID control technology. The target value of the feedback control unit is the reference input. The voltage across the Wheatstone bridge AC V AC The voltage V applied to the EF terminals of the Wheatstone bridge by the DAC bridge excitation module is the feedback input. EF As the feedback control quantity, the feedback control unit can convert the voltage V across the Wheatstone bridge AC into AC Stability control is at a set level.

[0009] Preferably, it also includes an ADC excitation voltage acquisition module for real-time acquisition of the voltage V across the Wheatstone bridge AC AC , as the input signal of the FPGA module feedback control unit.

[0010] Preferably, the FPGA module collects the voltage signal V according to the set target voltage and the voltage signal V collected by the ADC excitation voltage collection module. AC , the feedback control output voltage is calculated in real time, and then this voltage is applied to both ends of EF of the Wheatstone bridge through the DAC bridge excitation module. This voltage can be adjusted in real time.

[0011] Preferably, a temperature compensation mechanism is also included, and the temperature compensation mechanism offsets the resistance change caused by temperature change by adding a temperature compensation resistor in the bridge circuit.

[0012] Preferably, the temperature compensation mechanism uses a strain gauge with temperature compensation function, which is pasted at the measured point. When the temperature changes, the additional strain generated by the compensation gauge and the strain of the strain gauge offset each other, thereby achieving temperature compensation.

[0013] Preferably, the temperature compensation mechanism utilizes the property that the resistance of the thermistor changes with temperature to compensate for the change in resistance of the strain gauge caused by temperature change.

[0014] Preferably, the FPGA module is divided into multiple independent areas, and an independent configuration interface is provided for each area.

[0015] Preferably, the configuration data of the FPGA module is compressed by a compression algorithm to reduce the amount of data that needs to be loaded.

[0016] Compared with the prior art, the invention has the following beneficial effects: the invention can solve the problem of internal impedance of the cable, drift and nonlinearity of electronic devices, and interference caused by long-distance transmission by using a six-wire Wheatstone bridge. The six-wire Wheatstone bridge structure is used to eliminate the influence of wire resistance on the bridge excitation voltage, thereby improving the resolution and accuracy of long-distance strain measurement.

[0017] By utilizing the voltage PID feedback control structure, the bridge excitation voltage is stabilized, the drift and nonlinearity of electronic devices and the interference caused by long-distance transmission are reduced, and the resolution and accuracy of long-distance strain measurement are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the six-wire strain measurement and voltage compensation method of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] like Figure 1 As shown, a six-wire strain measurement and voltage compensation method comprises the following steps:

[0021] The Wheatstone bridge consists of three fixed resistors R1, R2, R3 and one variable resistor R4. R1 and R3 form one arm of the bridge, and R2 and R4 form the other arm of the bridge. R4 is a resistive strain gauge attached to the measured point. The voltage at the BD end of the Wheatstone bridge is measured by the ADC acquisition strain measurement module to calculate the resistance value of R4. Finally, the strain magnitude of the measured point is calculated by the FPGA module.

[0022] The DAC bridge excitation module provides the operating voltage for the EF ends of the Wheatstone bridge. The voltage is controlled by the FPGA module and can be adjusted in real time to maintain the voltage V across the AC ends of the Wheatstone bridge. AC To maintain the voltage at a set level, there is a feedback control unit inside the FPGA module to maintain the voltage at both ends of the Wheatstone bridge AC stable. The feedback control unit uses PID control technology. The target value of the feedback control unit is the reference input. The voltage V at both ends of the Wheatstone bridge AC is AC The voltage V applied to the EF terminals of the Wheatstone bridge by the DAC bridge excitation module is the feedback input. EF As the feedback control quantity, the feedback control unit can convert the voltage V across the Wheatstone bridge AC into AC Stable control at a set level. PID control technology (proportional-integral-differential control technology) is a feedback loop control strategy widely used in industrial control systems. It adjusts the output of the system through three control actions: proportional (P), integral (I) and differential (D) to reduce the system error, that is, the difference between the set value and the actual output. The design goal of the PID controller is to achieve fast response, high precision and good stability of the system.

[0023] The DAC bridge excitation module mainly provides the operating voltage V for both ends of the Wheatstone bridge EF. EF FPGA module collects the voltage signal V collected by the excitation voltage module according to the set target voltage and ADC AC , calculate the feedback control output voltage in real time, and then apply this voltage to both ends of EF of the Wheatstone bridge through the DAC bridge excitation module. This voltage can be adjusted in real time;

[0024] The ADC excitation voltage acquisition module mainly collects the voltage V at both ends of the Wheatstone bridge AC in real time. AC , as the input signal of the feedback control unit of the FPGA module;

[0025] The ADC acquisition strain measurement module is mainly used to measure the voltage V at the BD end of the Wheatstone bridge. BD , and then send the measured value to the FPGA module to solve the strain value of the measurement point;

[0026] The FPGA module is mainly used to calculate the size of the strain variable. At the same time, based on the data measured by the ADC acquisition excitation voltage module, it calculates the voltage size that the DAC bridge excitation module needs to feedback output, so that the voltage size collected by the ADC acquisition excitation voltage module remains stable.

[0027] The Wheatstone bridge is a circuit device used to accurately measure resistance. It consists of four resistors, usually marked as R1, R2, R3 and R4. When the bridge is balanced, the ratio of the currents in the bridge satisfies a specific relationship, that is, R1 / R2=R3 / R4, and no current flows through the diagonal lines of the bridge. By adjusting the resistance values ​​in the bridge, the value of the unknown resistance can be calculated. The Wheatstone bridge is not only used to measure resistance, but also can be used to measure physical quantities such as strain, temperature, humidity, etc. through sensors such as strain gauges. The sensitivity and accuracy of the bridge depends on multiple factors, including the quality of the resistor elements, the stability of the power supply, and the environmental conditions.

[0028] The Wheatstone bridge can measure resistance very accurately because the galvanometer causes current to flow only when the bridge is unbalanced, and this current is proportional to the difference in resistance value. In addition, the sensitivity of the bridge can be increased by adjusting the position of the galvanometer or using different known resistors.

[0029] In another embodiment, a temperature compensation mechanism is further included, which offsets the resistance change caused by temperature change by adding a temperature compensation resistor in the bridge circuit. A balanced bridge is established between the strain gauge and the compensation resistor. When the temperature changes, the resistance value of the compensation resistor changes, thereby unbalancing the bridge and generating a voltage signal opposite to the change in the resistance of the strain gauge, thereby achieving temperature compensation.

[0030] Specifically: In the thermocouple temperature measurement system, the compensation bridge method works by connecting an unbalanced bridge in series. The output voltage of this bridge will change with the change of the temperature of the cold end of the thermocouple, thereby correcting the error introduced by the cold end temperature fluctuation of the thermocouple. In strain gauge electrical measurement, bridge compensation or temperature compensation sheet can eliminate the influence of temperature change on the bridge output by connecting strain gauges and compensation strain gauges with the same material and the same temperature field in adjacent bridge arms or four bridge arms of the bridge. This method can be divided into compensation block compensation and working sheet compensation. In strain gauge sensors, bridge compensation achieves temperature compensation by adding a compensation resistor to the bridge circuit. The resistance value of the compensation resistor can be adjusted so that the output voltage of the sensor remains stable and accurate at different temperatures. The resistance value of the compensation resistor usually selected in this method is about 50% of the sensor resistance.

[0031] In general, bridge compensation adjusts the output of the bridge by measuring temperature or using a dedicated temperature compensation circuit to eliminate the impact of temperature changes on the bridge balance, thereby improving measurement accuracy.

[0032] In another embodiment, the temperature compensation mechanism uses a strain gauge with temperature compensation function, which is pasted at the measured point. When the temperature changes, the additional strain generated by the compensation gauge and the strain of the strain gauge offset each other, thereby achieving temperature compensation. This method is simple and easy to implement, and can provide good compensation effect in a large temperature range.

[0033] Specifically: In strain testing, eliminating the strain caused by temperature is called temperature compensation. Hardware compensation is a commonly used temperature strain compensation method in resistance strain testing. In the test, in order to make the compensation patch close to the test position and close to the powerless state, the compensation strain gauge and the test block with the same structure as the measured structure are usually pasted together. The structural strain sensed by the resistance strain gauge is reflected by the change in resistance value, but because the change in resistance value is extremely small, a circuit is introduced, usually a single-arm bridge test with a half-bridge circuit is used, and the resistance change is simulated and measured by amplifying the electrical signal.

[0034] Under the adjacent bridge arms, the compensation sheet and the working sheet are connected to the circuit at the same time to ensure voltage-free output. Because they are in the same temperature field, the two strain gauges are guaranteed to have the same resistance change value due to temperature change. Finally, only the corresponding value of the mechanical strain of the working strain gauge is output, thereby eliminating the temperature effect of the working sheet.

[0035] In another embodiment, the temperature compensation mechanism utilizes the property that the resistance of the thermistor changes with temperature to compensate for the resistance change of the strain gauge caused by the temperature change. By connecting the thermistor in series or in parallel with the strain gauge, when the temperature changes, the resistance of the thermistor will change, thereby compensating for the resistance change of the strain gauge.

[0036] Thermistors can be directly integrated into circuits to provide feedback of temperature information by measuring their resistance values ​​for compensation. Thermistors are usually low cost and easy to purchase. Thermistors can provide highly sensitive temperature detection within a small temperature range and are suitable for precise temperature control.

[0037] In another embodiment, the FPGA module is divided into multiple independent areas, and an independent configuration interface is provided for each area.

[0038] In traditional FPGA applications, once the configuration data is loaded, the FPGA's functions are fixed and cannot be changed at runtime. However, as application requirements continue to change, this static configuration method becomes increasingly inflexible. To solve this problem, dynamic partial reconfiguration technology was born.

[0039] The dynamic partial reconfiguration of this embodiment allows the configuration of a specific region of the FPGA to be updated while the FPGA is running without affecting the normal operation of other regions, bringing unprecedented flexibility to the FPGA, allowing the FPGA to dynamically adjust its functions without interrupting the overall operation.

[0040] The key to implementing dynamic partial reconfiguration is to divide the FPGA into multiple independent regions and provide an independent configuration interface for each region. In this way, when the configuration of a certain region needs to be updated, only the new configuration data needs to be loaded through the corresponding configuration interface without affecting the operation of other regions. This technology has great advantages for applications that require frequent changes in functions or algorithms. In terms of dynamic partial reconfiguration, the FPGA is divided into multiple independent regions and the configuration of a specific region is dynamically updated according to actual needs. This enables the FPGA to flexibly adjust its processing algorithms and parameters without interrupting communication.

[0041] In another embodiment, the configuration data of the FPGA module is compressed by a compression algorithm to reduce the amount of data that needs to be loaded.

[0042] When the FPGA is started, it needs to load configuration data from an external storage device, which usually takes a certain amount of time. In order to shorten the configuration time and increase the startup speed of the FPGA, configuration compression technology has emerged. This embodiment reduces the amount of data that needs to be loaded by compressing the configuration data, thereby reducing the configuration time.

[0043] There are many ways to implement configuration compression, among which run-length encoding and Huffman encoding are common. These compression algorithms can effectively reduce the redundant information in the configuration data and compress it into a more compact format. When the FPGA is started, the compressed configuration data is loaded into the FPGA, and then decompressed and configured. Although the decompression process will increase the time overhead, overall, the overall configuration time can still be significantly shortened due to the significant reduction in the amount of data transmitted. In terms of configuration compression, the configuration time is shortened by 30% by running-length encoding compression of the FPGA configuration data.

[0044] The present invention utilizes a six-wire Wheatstone bridge structure to eliminate the influence of wire resistance on the bridge excitation voltage, thereby improving the resolution and accuracy of long-distance strain measurement. The voltage PID feedback control structure is utilized to stabilize the bridge excitation voltage, reduce the drift and nonlinearity of electronic devices, and the interference caused by long-distance transmission, thereby improving the resolution and accuracy of long-distance strain measurement. Based on the traditional Wheatstone bridge, the present invention increases the PID feedback control circuit to keep the input voltage of the Wheatstone bridge stable, thereby greatly improving the precision and accuracy of strain measurement. The problem of limited accuracy and resolution of strain measurement over long distances is solved.

[0045] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A six-wire strain measurement and voltage compensation method, characterized in that: The steps include: The Wheatstone bridge consists of three fixed resistors R1, R2, R3 and one variable resistor R4. R1 and R3 form one arm of the bridge, and R2 and R4 form the other arm of the bridge. R4 is a resistive strain gauge attached to the measured point. The voltage at the BD end of the Wheatstone bridge is measured by the ADC acquisition strain measurement module to calculate the resistance value of R4. Finally, the strain magnitude of the measured point is calculated by the FPGA module. The DAC bridge excitation module provides the operating voltage for the EF ends of the Wheatstone bridge. The voltage is controlled by the FPGA module and can adjust the voltage in real time to maintain the voltage V across the AC ends of the Wheatstone bridge. AC Maintain a set voltage level.

2. A six-wire strain measurement and voltage compensation method according to claim 1, characterized in that: In order to maintain the voltage across the Wheatstone bridge AC stable, there is a feedback control unit inside the FPGA module. The feedback control unit adopts PID control technology. The target value of the feedback control unit is the reference input. The voltage across the Wheatstone bridge AC V AC The voltage V applied to the EF terminals of the Wheatstone bridge by the DAC bridge excitation module is the feedback input. EF As the feedback control quantity, the feedback control unit can convert the voltage V across the Wheatstone bridge AC into AC Stability control is at a set level.

3. A six-wire strain measurement and voltage compensation method according to claim 2, characterized in that: It also includes an ADC acquisition excitation voltage module for real-time acquisition of the voltage V across the Wheatstone bridge AC AC , as the input signal of the FPGA module feedback control unit.

4. A six-wire strain measurement and voltage compensation method according to claim 3, characterized in that: The FPGA module collects the voltage signal V collected by the ADC excitation voltage module according to the set target voltage. AC , the feedback control output voltage is calculated in real time, and then this voltage is applied to both ends of EF of the Wheatstone bridge through the DAC bridge excitation module. This voltage can be adjusted in real time.

5. A six-wire strain measurement and voltage compensation method according to claim 4, characterized in that: The invention also includes a temperature compensation mechanism, which offsets the resistance change caused by temperature change by adding a temperature compensation resistor in the bridge circuit.

6. A six-wire strain measurement and voltage compensation method according to claim 5, characterized in that: The temperature compensation mechanism uses a strain gauge with temperature compensation function, which is pasted at the measured point. When the temperature changes, the additional strain generated by the compensation gauge and the strain of the strain gauge offset each other, thereby achieving temperature compensation.

7. A six-wire strain measurement and voltage compensation method according to claim 5, characterized in that: The temperature compensation mechanism utilizes the property that the resistance of the thermistor changes with temperature to compensate for the change in resistance of the strain gauge caused by temperature change.

8. A six-wire strain measurement and voltage compensation method according to claim 4, characterized in that: The FPGA module is divided into multiple independent areas and an independent configuration interface is provided for each area.

9. A six-wire strain measurement and voltage compensation method according to claim 4, characterized in that: The configuration data of the FPGA module is compressed through a compression algorithm to reduce the amount of data that needs to be loaded.

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