Strain micro-signal identification and measurement circuit and method based on reference power supply self-compensation

Abstract

The invention discloses a strain micro-signal identification and measurement circuit and method based on reference power supply self-compensation, and the circuit comprises a Wheatstone bridge and a strain measurement circuit, the Wheatstone bridge is composed of strain gauges, and the strain measurement circuit is connected with the Wheatstone bridge to collect and process a strain signal. The strain measurement circuit comprises a signal conditioning circuit, a digital processing circuit and a power supply circuit. The low-noise, low-drift and high-precision reference voltage is simultaneously accessed to the Wheatstone bridge excitation and the reference voltage input end of the analog-to-digital converter, and the amplitude change is self-compensated without influencing the measurement precision. And by utilizing a measuring circuit self-compensation technology, zero drift caused by temperature change and long-time operation is effectively eliminated, and the measuring precision is improved. And the temperature drift and the time drift have qualitative leap. By monitoring the strain measuring points in real time and transmitting the strain data to the receiving end in real time, the real-time monitoring of the strain state of the measured object is realized. Influences of long cable signal attenuation, impedance change and the like on measurement precision in wired transmission are avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of strain measurement, and particularly relates to a strain micro-signal identification measurement circuit and method based on benchmark power supply self-compensation. BACKGROUND

[0002] A strain measurement system is a device used to measure the strain of an object under the action of force or other physical factors. It is mainly composed of a strain gauge, a measurement circuit, and a data acquisition and processing unit. When the measured object is deformed under the action of external force, the strain gauge pasted on the surface of the object will also be deformed. The resistance value of the strain gauge will change accordingly according to the degree of deformation. This resistance change is converted into a change in voltage or current by the measurement circuit. The data acquisition and processing unit collects, quantizes, and analyzes these changing electrical signals, and finally calculates the strain value of the object. For example, in a metal strain gauge, when the metal wire is stretched, its length increases and its cross-sectional area decreases, resulting in an increase in resistance; conversely, the resistance decreases. According to the specific relationship between resistance change and strain, the strain of the object can be determined by measuring the resistance change. It is often used in aerospace, mechanical engineering, civil engineering, etc.

[0003] When collecting strain signals, temperature drift and time drift are two common problems that affect the accuracy and reliability of the measurement. First, the resistance value of the strain gauge will change with temperature, which is due to the change of the resistivity of the metal material with temperature and the difference in the thermal expansion coefficient of the strain gauge and the measured object. For example, when the temperature rises, the resistivity of the metal resistance wire generally increases, resulting in an increase in the resistance value of the strain gauge, thus producing a false strain signal. Second, the parameters of the components in the measurement circuit may also change with temperature, such as the gain and zero point of the amplifier. These changes will cause the output of the measurement system to drift, affecting the accurate measurement of the strain signal. Since the data drifts over time, the regularity of the measurement data becomes poor, making it difficult to accurately extract useful information.

[0004] The current common solution is to calibrate the measurement system periodically by comparing it with a standard strain source, adjusting the zero point and gain of the measurement system to correct the errors caused by time drift. The calibration frequency should be determined according to the stability and usage frequency of the measurement system. Selecting a reliable and aged strain gauge can also reduce the time drift caused by the aging of the strain gauge. Before formal measurement, the measurement system is preheated and tested for stability for a long time to observe its drift over time, and the measurement data is corrected in real time through software algorithms to improve the accuracy of the measurement.

[0005] High-quality measuring instruments usually have better stability and lower time drift characteristics. Although the above-mentioned common solutions can reduce the influence of temperature drift and time drift on measurement accuracy to some extent, they greatly increase the complexity of the strain measurement system. Therefore, the present method also proposes a strain micro-signal recognition method based on reference power supply self-compensation to realize the circuit self-compensation function of the strain measurement system, and finally realize high precision, high resolution and wide measurement range.

[0006] On the other hand, wireless strain measurement is a technology that measures and monitors the strain state of an object through wireless communication technology, with the advantages of convenience, flexibility, remote operation, etc., and has been widely used in aerospace, civil engineering, mechanical engineering, biomedical engineering and other fields. Zigbee wireless strain measurement technology has the advantages of low power consumption, self-organizing network and low cost. In bridge engineering applications, Zigbee wireless strain measurement devices are installed at key parts of the bridge, such as piers, main beams and cables, to build a wireless strain measurement network. These strain measurement devices can collect strain data of the bridge structure under the action of vehicle load, wind load, temperature change, etc. in real time, and transmit them to the monitoring center through the Zigbee network. In construction engineering applications, Zigbee wireless strain measurement devices are arranged at the frame structure and shear wall of high-rise buildings, large industrial plants and other building structures to monitor the strain of the structure under the action of self-weight, wind load, seismic load, etc. in real time. In mechanical engineering applications, Zigbee wireless strain measurement devices are installed on the key components (such as shafts, gears, blades, etc.) of large mechanical equipment such as generators, steam turbines and compressors to monitor the strain of the equipment during operation in real time and discover fatigue damage and fault hazards of the components in a timely manner.

[0007] Strain measurement is a technique that obtains the internal stress state of an object by measuring the small deformation of the object under force. The commonly used strain measurement method is to use a resistance strain gauge. When the strain gauge is pasted on the surface of the measured object, the deformation of the object will cause the resistance of the strain gauge to change. The strain of the object is calculated by measuring the resistance change. Zero drift in strain measurement refers to the phenomenon that the output zero point of the measurement system shifts over time, environmental temperature and other factors during the strain measurement process. Zero drift will cause errors in the measurement results, especially in long-term measurement processes, zero drift may accumulate, leading to a significant decrease in measurement accuracy. For some occasions that require high-precision measurement, such as aerospace, precision machining and other fields, zero drift may affect the quality and performance of the product. Zero drift will make the stability of the measurement data worse, making data analysis and processing difficult. When analyzing a large amount of measurement data, zero drift may mask the true strain signal, making data processing and feature extraction complex, and even leading to incorrect conclusions. SUMMARY

[0008] The technical problem solved by the present application is to provide a strain micro-signal identification measurement circuit and method based on reference power supply self-compensation, which solves the problems of temperature drift and time drift in the existing strain measurement system, solves the problems of wiring difficulty, cable damage, etc. in engineering applications, and realizes extremely low zero drift by using self-compensation technology, thereby improving the precision of engineering measurement.

[0009] Technical scheme: In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0010] A strain micro-signal identification measurement circuit based on reference power supply self-compensation, comprising a Wheatstone bridge and a strain measurement circuit, the Wheatstone bridge being composed of strain gauges, and the strain measurement circuit being connected to the Wheatstone bridge to collect and process strain signals, the strain measurement circuit comprising a signal conditioning circuit, a digital processing circuit and a power supply circuit.

[0011] Further, the Wheatstone bridge is composed of four resistors, which are strain gauge resistors or elements related to strain gauge resistors.

[0012] Further, the signal conditioning circuit comprises a common-mode and differential-mode filter circuit, a resistance-capacitance filter circuit and an analog-to-digital converter, the Wheatstone bridge being connected to the analog-to-digital converter through the common-mode and differential-mode filter circuit and the resistance-capacitance filter circuit; the analog-to-digital converter collecting the output voltage of the Wheatstone bridge.

[0013] Further, the reference voltage is connected to the Wheatstone bridge excitation and the reference voltage input end of the analog-to-digital converter at the same time, the reference voltage of the Wheatstone bridge excitation and the analog-to-digital converter being homologous, so that the amplitude change is self-compensated without affecting the measurement precision.

[0014] Further, the analog-to-digital converter adopts an analog-to-digital converter of model ADS1220IPWR, the AIN1 and AIN2 ports of the analog-to-digital converter collecting strain signals, and the voltage output end of the Wheatstone bridge being connected to the AIN1 and AIN2 ports of the analog-to-digital converter after interference is filtered out by the common-mode and differential-mode filter circuit.

[0015] Further, the digital processing circuit comprises a main processor and a memory; the main processor being connected to the analog-to-digital converter to drive the analog-to-digital converter to complete strain signal collection; and the main processor being connected to a ZIGBEE wireless transceiver module to realize wireless transmission of strain data.

[0016] Further, the main processor adopts a main processor of model STM32F429ZGT6, and the SPI4 and SPI5 interfaces of the main processor are respectively connected to a plurality of analog-to-digital converters to drive the analog-to-digital converters to complete strain signal collection.

[0017] Further, Zigbee wireless transceiver module is further included, the FSMC interface of the main processor is connected with the memory, the USART2 interface is connected with the ZIGBEE wireless transceiver module, the ZIGBEE wireless transceiver module is driven, and wireless sending of strain data is realized.

[0018] The FSMC interface of the main processor is connected with the memory, the USART2 interface is connected with the ZIGBEE wireless transceiver module, the ZIGBEE wireless transceiver module is driven, and wireless sending of strain data is realized.

[0019] Further, the power supply circuit includes a surge protection circuit, an overvoltage, undervoltage and reverse connection protection circuit, a common mode and differential mode filter circuit and a power supply conditioning circuit.

[0020] A strain micro-signal identification measurement method based on reference power supply self-compensation is realized by the above-mentioned circuit, each measurement channel is excited by a low-noise, low-drift and high-precision reference voltage of Wheatstone bridge, and the low-noise, low-drift and high-precision reference voltage is simultaneously connected to the reference voltage input end of the Wheatstone bridge excitation and the analog-to-digital converter, so that not only the long-term stability and temperature stability are ensured, but also if the reference chip changes in amplitude due to external changes, since the Wheatstone bridge excitation and the reference voltage of the analog-to-digital converter are homologous, the change in amplitude can be self-compensated without affecting the measurement accuracy.

[0021] Advantages: compared with the prior art, the present application has the following advantages:

[0022] The strain micro-signal identification measurement circuit based on reference power supply self-compensation has a maximum change of 0.3με in strain value in a temperature change range of-20 DEG C to +85 DEG C, and the temperature drift performance index is 173 times higher than that of the prior art. In a 25 DEG C temperature environment, the maximum change of strain value is 0.1με after continuous operation for one week, and the time drift performance index is 190 times higher than that of the prior art. Therefore, the improved circuit and method of the present application have a qualitative leap in temperature drift and time drift performance. The circuit self-compensation function of the strain measurement system is realized, and finally high-precision, low-drift, high-resolution and wide measurement range are realized.

[0023] The strain micro-signal identification measurement circuit based on reference power supply self-compensation utilizes Zigbee wireless communication technology, breaks away from the complex wired connection in traditional strain measurement, solves the problems of wiring difficulty and cable damage, and is especially suitable for distributed strain measurement of large structures such as bridges and buildings. Strain data of each measurement point can be conveniently wirelessly transmitted to a central monitoring system, and the installation and maintenance costs are reduced. By using the measurement circuit self-compensation technology, the zero drift caused by temperature change and long-time operation is effectively eliminated, and the measurement accuracy is improved.

[0024] The application realizes real-time monitoring of the strain state of the measured object by real-time monitoring of the strain measuring point and real-time transmission of the strain data to the receiving end. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a schematic diagram of Wheatstone bridge.

[0026] Figure 2 It is a schematic diagram of using low-noise, low-drift, high-precision reference voltage to excite Wheatstone bridge.

[0027] Figure 3 It is a schematic diagram of a commonly used strain circuit measurement method.

[0028] Figure 4 It is a schematic diagram of a strain measurement circuit self-compensation.

[0029] Figure 5 It is a hardware block diagram of the strain measurement system of embodiment 1.

[0030] Figure 6 It is a whole framework diagram of the strain measurement technology based on Zigbee wireless transmission of embodiment 2.

[0031] Figure 7 It is a hardware block diagram of the strain measurement system of embodiment 2

[0032] Figure 8 It is a schematic diagram of a signal conditioning circuit.

[0033] Figure 9 It is a schematic diagram of the internal structure of ADS1220IPWR analog-to-digital converter.

[0034] Figure 10 It is the performance parameters of REF195FSZ-REEL.

[0035] Figure 11 It is a schematic diagram of the digital processing circuit of the strain measurement system of embodiment 1.

[0036] Figure 12 It is a schematic diagram of the digital processing circuit of the strain measurement system of embodiment 2.

[0037] Figure 13 It is a digital circuit interface connection diagram of embodiment 1.

[0038] Figure 14 It is a digital circuit interface connection diagram of embodiment 2.

[0039] Figure 15 It is a schematic diagram of a power supply circuit.

[0040] Figure 16 The mSATA connector circuit schematic diagram for example 2.

[0041] Figure 17 The Zigbee transceiver module circuit schematic diagram for example 2. DETAILED DESCRIPTION

[0042] The application will be further illustrated below in conjunction with specific examples, which are implemented on the premise of the technical scheme of the application, and should be understood that the examples are only used to illustrate the application and not to limit the scope of the application.

[0043] Example 1

[0044] The strain micro-signal recognition measurement circuit based on reference power supply self-compensation of the application mainly comprises a Wheatstone bridge and a strain measurement circuit. The strain gauge forms the Wheatstone bridge, and the strain measurement circuit connects the Wheatstone bridge to collect and process the strain signal. The strain measurement circuit comprises three parts, the first part is a signal conditioning circuit, the second part is a digital processing circuit, and the third part is a power supply circuit.

[0045] As shown in Figure 1 and 2 , the Wheatstone bridge excitation design: in the strain measurement system, the strain gauge usually forms a Wheatstone bridge form, and the Wheatstone bridge is composed of four resistors, which are strain gauge resistors or elements related to strain gauge resistors.

[0046] The basic principle of the Wheatstone bridge is based on the bridge balance condition. In the initial state, the four arm resistors of the bridge satisfy a certain relationship, so that the output voltage of the bridge is zero, that is, the bridge is in a balanced state. When the strain gauge is deformed by external force, its resistance value will change, thereby breaking the balance of the bridge, and the bridge outputs a voltage signal proportional to the change of the strain gauge resistance. By measuring this output voltage signal, the strain experienced by the strain gauge can be calculated.

[0047] The bridge voltage provides working voltage for the strain gauge and other resistance elements in the bridge. When the strain gauge changes in resistance under the action of external force, the bridge will produce corresponding output voltage change under the action of the bridge voltage. The bridge voltage is the energy basis for generating the measurement signal. Without sufficient bridge voltage, the bridge cannot work normally, and the output signal corresponding to the resistance change of the strain gauge cannot be detected.

[0048] The bridge voltage stability of the bridge excitation ultimately determines the stability of the Wheatstone bridge output voltage signal, and there are two common bridge voltage excitation methods, one is that the entire strain measurement system is powered by a high-power DC-DC power supply, and the other is that the entire strain measurement system is powered by a low-noise LDO power supply, the first one uses a high-power DC-DC power supply, although it meets the requirements of the Wheatstone bridge in power consumption, but the DC-DC power supply has the defects of large ripple noise, and the output voltage fluctuates greatly with the change of temperature, the second low-noise LDO meets the requirements of strain measurement in noise ripple, but the power consumption of the low-noise LDO itself is a problem when it powers the entire system of the Wheatstone bridge, and the output voltage of the low-noise LDO will fluctuate with the change of the load, and the temperature drift and time drift performance are not good.

[0049] In view of the defects in the prior art, the present application needs to solve the problems of Wheatstone bridge excitation source power consumption, noise, temperature drift and time drift, so a scheme of using low-noise, low-drift and high-precision reference voltage to excite the Wheatstone bridge for each measurement channel is proposed, as shown in Figure 4

[0050] In the specific circuit implementation, in the embodiment, the hardware framework of the strain measurement circuit is as shown in Figure 5 , which mainly consists of four parts, the first part is a signal conditioning circuit, including a common-mode differential-mode filter circuit, a resistance-capacitance filter circuit and an ADS1220 analog-to-digital converter. The second part is a digital processing circuit, which is composed of an STM32F429ZGT6 main processor and a W9825G6KH-6I memory, and the third part is a power supply circuit, which is mainly composed of a 2KV surge protection circuit, an overvoltage, undervoltage and reverse connection protection circuit, a common-mode differential-mode filter circuit and a power supply conditioning circuit.

[0051] First part: signal conditioning circuit

[0052] The signal conditioning circuit includes a common-mode differential-mode filter circuit, a resistance-capacitance filter circuit and an analog-to-digital converter. The analog converter is connected to the Wheatstone bridge to collect the output voltage of the Wheatstone bridge. The amplification circuit and the filter circuit are integrated in the analog-to-digital converter, and a high-precision reference voltage is connected to the Wheatstone bridge excitation and the reference voltage input end of the analog-to-digital converter at the same time, to ensure the consistency of the Wheatstone bridge excitation and the reference voltage of the analog-to-digital converter.

[0053] As shown in Figure 3 , the existing common strain measurement circuit mainly includes an amplifier circuit, a filter circuit and an analog-to-digital converter.

[0054] ​Amplifier circuit: Because the strain gauge produces a very weak electrical signal, it needs to be amplified to a measurable and processable level by an amplifier. The amplifier circuit can be divided into linear amplifier and logarithmic amplifier according to its working principle, and the commonly used amplifier is operational amplifier. The operational amplifier compares and amplifies the input strain signal with the feedback signal, and outputs an amplified signal, and the amplification factor is determined by the ratio of the feedback resistance and the input resistance in the circuit.

[0055] Filter circuit: The filter circuit is used to filter out the noise and interference signals mixed in the measurement circuit, and retain the useful strain signal. According to its filtering characteristics, it can be divided into low-pass filter, high-pass filter, band-pass filter and band-stop filter, etc. For example, the low-pass filter allows low-frequency strain signals to pass through, while blocking high-frequency noise and interference signals; The high-pass filter allows high-frequency signals to pass through, and blocks low-frequency signals. The band-pass filter only allows signals within a certain frequency range to pass through, while the band-stop filter blocks signals within a certain frequency range.

[0056] Analog-to-digital conversion circuit: The analog strain signal after amplification and filtering is converted into a digital signal for processing, storage and display by a computer or other digital processing device. The analog-to-digital conversion circuit is usually composed of a sample and hold circuit, a quantizer and an encoder. The sample and hold circuit samples the analog signal and keeps the sample value unchanged during quantization and encoding; The quantizer converts the analog signal amplitude sampled into discrete digital quantities; The encoder encodes the quantized digital quantity into binary code that can be recognized by the computer.

[0057] The commonly used strain measurement circuit scheme will have a slow and irregular change in the output signal over time or environmental factors during strain measurement, which is not caused by the real change of the measured strain. The causes include temperature change, power supply voltage fluctuation, electronic component aging, mechanical vibration and impact, etc. Therefore, the commonly used strain measurement circuit needs to be calibrated and updated regularly or anti-vibration and reinforcement measures.

[0058] The present application simplifies the commonly used strain measurement circuit, reduces the overall impact of the separation device on the measurement system, and proposes to use a low-current consumption, programmable gain, high-resolution, 50Hz and 60Hz suppression analog-to-digital converter to directly collect the voltage output by the Wheatstone bridge. The amplification circuit and the filter circuit are integrated inside the analog-to-digital converter, the amplification circuit uses the programmable gain inside the analog-to-digital converter to realize, and the filter circuit uses the high-order digital filter inside the analog-to-digital converter to realize.

[0059] As Figure 4As shown, the embodiment realizes the self-compensation of the measurement circuit. The reference voltage of the analog-to-digital converter is a key parameter in the conversion process of the analog-to-digital converter, which provides a reference for the conversion of the analog signal to the digital signal. The reference voltage determines the voltage range of the analog signal that can be converted by the analog-to-digital converter. The stability of the reference voltage is crucial to the conversion accuracy of the analog-to-digital converter. Stable reference voltage can ensure that the analog-to-digital converter produces consistent digital output for the same analog input signal under different time and environmental conditions. If the reference voltage fluctuates, it will cause errors in the conversion result, just like using a ruler with unstable scale to measure objects, the result will inevitably be inaccurate. The reference voltage needs long-term stability and temperature stability. The reference voltage source with good long-term stability can maintain the stability of the voltage value during long-term use, reducing the measurement error caused by time lapse. Temperature stability refers to the degree of change of the reference voltage under different temperature environments. For devices working in a wide temperature range, such as sensor nodes in industrial sites, a reference voltage source with small temperature coefficient needs to be selected to ensure that the analog-to-digital converter can work accurately under various environmental temperatures. In summary, the reference voltage of the analog-to-digital converter and the Wheatstone bridge excitation have consistent performance requirements, both of which require long-term stability and temperature stability.

[0060] As shown in the figure, the reference voltage of the analog-to-digital converter is connected to the reference voltage input terminal of the analog-to-digital converter. Figure 4 As shown in the figure, the reference voltage of the analog-to-digital converter is connected to the reference voltage input terminal of the analog-to-digital converter. Figure 5 As shown in the figure, the reference voltage of the analog-to-digital converter is connected to the reference voltage input terminal of the analog-to-digital converter.

[0061] As shown in the figure, the reference voltage of the analog-to-digital converter is connected to the reference voltage input terminal of the analog-to-digital converter. Figure 8 As shown in the figure, the reference voltage of the analog-to-digital converter is connected to the reference voltage input terminal of the analog-to-digital converter.

[0062] As shown in the figure, the reference voltage of the analog-to-digital converter is connected to the reference voltage input terminal of the analog-to-digital converter. Figure 8As shown, the common mode and differential mode filter circuit mainly includes capacitor C7, capacitor C9, capacitor C12, inductor L1, capacitor C10, resistor R1, resistor R2, capacitor C11, capacitor C8, capacitor C13. Capacitor C9 is connected in parallel to the 7th pin and the 5th pin of the Wheatstone bridge terminal, and connects the voltage output end of the Wheatstone bridge. One end of capacitor C7 and capacitor C12 is connected to capacitor C9, and the other end is grounded. The input end of inductor L1 is connected to capacitor C9, the output end is connected to capacitor C10, one end of resistor R1 is connected to the output end of inductor L1, the other end is connected to capacitor C11, and then connected to the AIN1 port of ADS1220IPWR analog-to-digital converter. One end of resistor R2 is connected to the output end of inductor L1, the other end is connected to capacitor C11, and then connected to the AIN2 port of ADS1220IPWR analog-to-digital converter. One end of capacitor C8 is grounded, and the other end is connected to capacitor C11. One end of capacitor C13 is grounded, and the other end is connected to capacitor C13. The common mode and differential mode filter circuit can filter out common mode and differential mode interference, make the useful signal more pure, and thus improve the transmission quality and reliability of the signal. Especially in some circuits with high signal accuracy requirements, such as strain micro-signal acquisition circuit, high-speed data transmission circuit, etc., the common mode and differential mode filter circuit plays an important role. The signal passing through the common mode and differential mode filter circuit enters the ADS1220IPWR analog-to-digital converter.

[0063] As shown in Figure 5 and 9 The connection relationship of the signal conditioning circuit of ADS1220IPWR analog-to-digital converter and the internal structure of ADS1220IPWR analog-to-digital converter are shown respectively. AIN1 and AIN2 of ADS1220IPWR analog-to-digital converter are used to collect strain signals, and the voltage output end of the Wheatstone bridge is connected to the AIN1 and AIN2 ports of ADS1220IPWR analog-to-digital converter through the 7th pin and the 5th pin of the Wheatstone bridge terminal and the common mode and differential mode filter circuit to filter out interference. DIN, SCLK, DOUT, CS pins of ADS1220IPWR analog-to-digital converter are SPI standard interfaces, and DRDY is the conversion completion flag bit of ADS1220IPWR analog-to-digital converter.

[0064] REFP1 and REFN1 are used as reference reference, and the reference reference and Wheatstone bridge excitation are powered by voltage reference source REF195FSZ-REEL. REFN1 is connected to the negative end of the Wheatstone bridge through the 3rd port of the Wheatstone bridge terminal. The output end of voltage reference source REF195FSZ-REEL is connected to REFP1 through capacitor C1 and capacitor C2.

[0065] The ADS1220IPWR analog-to-digital converter has a built-in maximum gain setting of 128 times, which can directly amplify the weak strain signal by 128 times. It has a resolution of 24 bits, and most importantly, the ADS1220IPWR analog-to-digital converter has a temperature drift of 0.08 μV / °C and a time drift of 0.110 ppm / h. The performance parameters of the voltage reference source REF195FSZ-REEL are shown in Figure 10 The temperature drift is 2 ppm / °C, and the noise ripple is 50 uVp-p. The REF195FSZ-REEL also has an output current capability of 30 mA. The power consumption of the ADS1220IPWR analog-to-digital converter is up to 890 uA, which means that the 30 mA output current can basically be provided to the Wheatstone bridge, suitable for all strain measurement applications above 350 ohms.

[0066] Second part: digital processing circuit

[0067] The digital processing circuit includes a main processor of STM32F429ZGT6 model, a memory of W9825G6KH-6I SDRAM model, an Ethernet chip of LAN8720AI-CP-TR, etc. The main processor is connected to the analog-to-digital converter to drive the analog-to-digital converter to complete strain signal acquisition; the main processor is connected to the ZIGBEE wireless transceiver module to realize wireless transmission of strain data; the main processor is connected to the memory and the Ethernet chip.

[0068] As shown in Figure 11 and Figure 13 , they are the digital processing circuit schematic diagram and specific connection mode of the strain measurement system respectively. The digital processing circuit is mainly composed of an STM32F429ZGT6 main processor and peripheral devices. The digital processing circuit uses 2 SPI interfaces, 1 FSMC interface, and 1 UART interface. The specific connection mode is shown in Figure 11 .

[0069] The SPI4 interface connects 4 ADS1220IPWR analog-to-digital converters, and drives the first 4 ADS1220IPWR analog-to-digital converters to complete 4-channel strain signal acquisition.

[0070] The SPI5 interface connects 4 ADS1220IPWR analog-to-digital converters, and drives the other 4 ADS1220IPWR analog-to-digital converters to complete 4-channel strain signal acquisition.

[0071] The FSMC interface connects the memory of W9825G6KH-6I SDRAM model, and drives the W9825G6KH-6I SDRAM as the software program running memory.

[0072] SDIO: The SDIO interface drives the TF card to realize the storage of strain data.

[0073] RGMII: RGMII interface drive LAN8720AI-CP-TR Ethernet chip to realize the network communication of strain data.

[0074] Fourth part: power supply circuit

[0075] As Figure 15 shown, the power supply circuit design of the strain measurement system mainly includes four parts:

[0076] The first part of the surge protection circuit: the 2KV surge protection circuit of the embodiment mainly includes fuse F17, voltage-dependent resistor M1, inductor L10, and diode D19. Fuse F17 adopts JFC2410-1200TS, and the fuse is in the first stage of the protection circuit. Voltage-dependent resistor M1 adopts FTR14D470K, with a maximum current capacity of 2KA; L10 is a decoupling inductor, and D19 is a TVS diode, providing precise protection.

[0077] In the surge protection circuit, it is recommended to choose a slow-melting fuse instead of a fast-melting fuse. Because the surge current or impulse current has a very high peak current, but its appearance time is very short, and ordinary fuse cannot withstand such current. But if you replace it with a large-specification current fuse, it cannot protect the circuit when an overload current occurs. Selecting a slow-melting fuse can withstand instantaneous pulse current, thereby ensuring the normal operation of the equipment. Here, because the slow-melting fuse has a large nominal melting heat energy value I 2 t, it requires a large amount of energy to melt, so it has strong pulse resistance. The nominal melting heat energy is the most important parameter when selecting a lightning protection fuse. Fuse F17 adopts JFC2410-1200TS, and the fuse is in the first stage of the protection circuit.

[0078] The second part of the overvoltage, undervoltage, and reverse connection protection circuit mainly includes resistors R104, R107, R108, voltage converter U44, and diode D18. U44 is a synchronous step-down DC-DC converter with model number MAX17609ATC+T, which is designed for overvoltage, undervoltage, and reverse connection protection of the total power supply. MAX17609ATC+T power electronic switch supports a power supply input range of 4.5V to 60V, a continuous current of 1A, programmable overvoltage and undervoltage design, and integrated reverse protection function. Resistors R104, R107, and R108 are programming resistors, with an overvoltage threshold of 20V and an undervoltage threshold of 7V. D18 is a switching MOS tube.

[0079] The third part of the common mode and differential mode filter circuit mainly includes capacitors C327, C328, C323, inductor L12, capacitors C329, C330, C325, C326, etc., and the connection mode is asFigure 12 As shown, it is a conventional connection mode, and will not be repeated.

[0080] The fourth part of the power supply conditioning circuit: mainly includes synchronous buck converter U45 and low dropout linear regulator U46, U45 model is TPS54302DDCR, 9-18V input voltage is regulated to 6V voltage, low dropout linear regulator U46 model is AMS1117-3.3, generates 3.3V voltage to power supply for digital circuit.

[0081] Example 2

[0082] The strain micro-signal identification measurement method based on reference power supply self-compensation of the embodiment is based on the circuit implementation of the embodiment.

[0083] Each measurement channel adopts low-noise, low-drift, high-precision reference voltage to excite the Wheatstone bridge, and the low-noise, low-drift, high-precision reference voltage is connected to the reference voltage input end of the Wheatstone bridge excitation and the analog-to-digital converter at the same time, which not only ensures long-term stability and temperature stability, but also can self-compensate the amplitude change caused by the reference chip due to external changes without affecting the measurement accuracy because the Wheatstone bridge excitation and the reference voltage of the analog-to-digital converter are homologous. See the specific content in Example 1.

[0084] In the development and test stage of the method, the application and the other two conventional strain measurement systems (devices using DC-DC excitation and LDO excitation and regular calibration) are tested for temperature drift, and the test data is shown in Table 1.

[0085] In the development and test stage of the application, the application and the other two conventional strain measurement systems (devices using DC-DC excitation and LDO excitation and regular calibration) are tested for time drift, and the test data is shown in Table 2.

[0086] Table 1. Temperature drift test of different strain measurement systems

[0087]

[0088]

[0089] Table 2. Time drift test of different strain measurement systems

[0090]

[0091] As shown in Table 1, the strain micro-signal identification invention method based on the reference power supply self-compensation has a maximum change of 0.3με in a temperature change range of-20℃ to +85℃, while the other two strain measurement circuits with separated device design have a maximum change of 71με for a DC-DC power supply measurement system and a maximum change of 52με for an LDO power supply measurement system, and the temperature drift performance index is improved by 173 times.

[0092] As shown in Table 2, the strain micro-signal identification invention method based on the reference power supply self-compensation has a maximum change of 0.1με in a 25℃ temperature environment for continuous operation for one week, while the other two strain measurement circuits with separated device design have a maximum change of 48με for a DC-DC power supply measurement system and a maximum change of 19με for an LDO power supply measurement system, and the time drift performance index is improved by 190 times.

[0093] The application has been successfully applied to a large bridge strain monitoring system project of a scientific research unit to monitor the strain change of the bridge in the construction process, ensure the construction safety and quality, find potential problems in time and take measures to adjust. The actual working state of the bridge in the use stage is evaluated, the strain response of the bridge structure under the action of vehicle load, wind load, temperature change and other factors is understood, and whether the bridge is in a safe operation state is judged. At present, it has been continuously operated for half a year, and not only the measurement data accuracy but also the system drift parameters are unanimously recognized by the customer, and the scientific research unit is also successively purchasing the equipment applying the application, and a production value of nearly one million yuan is created.

[0094] Embodiment 3

[0095] Different from embodiment 1, the embodiment adds a Zigbee wireless transceiver module to realize wireless transmission of data on the basis of embodiment 1.

[0096] The technical block diagram of the extremely low zero drift strain measurement technology based on Zigbee wireless transmission is shown in the figure and mainly includes a plurality of strain measurement terminals and a plurality of strain gauge measurement points. Figure 6

[0097] The strain micro-signal identification measurement circuit based on the reference power supply self-compensation of the application mainly includes a Wheatstone bridge and a strain measurement circuit. The strain gauge forms the Wheatstone bridge, and the strain measurement circuit connects the Wheatstone bridge to collect and process the strain signal. The strain measurement circuit includes four parts, the first part is a signal conditioning circuit, the second part is a digital processing circuit, the third part is a power supply conditioning circuit, and the fourth part is a Zigbee wireless transceiver module.

[0098] In the specific circuit implementation, in the embodiment, the hardware framework of the strain measurement circuit is as shown in the figure.​Figure 6 As shown, mainly consists of four parts, the first part is signal conditioning circuit, including common mode differential mode filter circuit, resistance-capacitance filter circuit and ADS1220 analog-to-digital converter. The second part is digital processing circuit, the circuit is composed of STM32F429ZGT6 main processor, W9825G6KH-6I memory, the third part is power conditioning circuit, mainly by 2KV surge protection circuit, overvoltage, undervoltage, reverse connection protection circuit, common mode differential mode filter circuit, power conditioning circuit. The fourth part is Zigbee wireless transceiver module,

[0099] The first part: the signal conditioning circuit part is the same as embodiment 1, and is described with reference to embodiment 1

[0100] The second part: digital processing circuit

[0101] The digital processing circuit includes a main processor of STM32F429ZGT6 type, a memory of W9825G6KH-6I SDRAM type and the like. The main processor is connected with the analog-to-digital converter, drives the analog-to-digital converter to complete strain signal acquisition; the main processor is connected with the ZIGBEE wireless transceiver module, realizes wireless sending of strain data; and the main processor is connected with the memory.

[0102] As Figure 12 and Figure 14 shown, respectively, are the digital processing circuit principle diagram and the specific connection mode of the strain measurement system, the digital processing circuit is mainly composed of an STM32F429ZGT6 main processor and peripheral devices, the digital processing circuit uses 2 SPI interfaces, 1 FSMC interface and 1 UART interface, and the specific connection mode is as shown in Figure 13

[0103] The SPI4 interface is connected with 4 ADS1220IPWR analog-to-digital converters, drives the first 4 ADS1220IPWR analog-to-digital converters to complete 4-way strain signal acquisition.

[0104] The SPI5 interface is connected with 4 ADS1220IPWR analog-to-digital converters, drives the other 4 ADS1220IPWR analog-to-digital converters to complete 4-way strain signal acquisition.

[0105] The FSMC interface is connected with a memory of W9825G6KH-6I SDRAM type, drives the W9825G6KH-6I SDRAM as program running memory.

[0106] The USART2 interface is connected with the ZIGBEE wireless transceiver module, the USART2 interface drives the ZIGBEE wireless transceiver module, realizes wireless sending of strain data.

[0107] ​Part III: The power supply circuit is the same as that of Embodiment 1, and is described with reference to Embodiment 1

[0108] Part IV: Zigbee wireless transceiver module

[0109] The Zigbee wireless transceiver module includes a Zigbee wireless transceiver circuit and an mSATA connector, as shown in Figure 16 The circuit schematic diagram of the mSATA connector of Model 1775862-2 is shown in Figure 17 The Zigbee wireless transceiver circuit schematic diagram is shown in

[0110] The Zigbee wireless transceiver module uses a standard mSATA connector to realize the free configuration of the module. The mSATA connector uses the Model 1775862-2 of Tyco Electronics, wherein the port correspondence between the Zigbee wireless transceiver circuit and the mSATA connector is as follows:

[0111] The PA2 / USART2_TX port of the mSATA connector is connected to the 25 port (RX) of the Zigbee wireless transceiver main processor.

[0112] The PA2 / USART2_RX port of the mSATA connector is connected to the 26 port (TX) of the Zigbee wireless transceiver main processor.

[0113] The RESET_ZIGBEE port of the mSATA connector is connected to the 11 port (RESETn) of the Zigbee wireless transceiver main processor.

[0114] The PA1 / USART2_RTS port and the PD3 / USART2_CTS of the mSATA connector are not electrically connected to the Zigbee wireless transceiver main processor.

[0115] The PA1 / USART2_RTS port, the PA2 / USART2_TX port, and the PA3 / USART2_RX port complete the data interaction with the main processor and the Zigbee wireless transceiver module, and the RESET_ZIGBEE port completes the function reset of the Zigbee module by the main processor. Specifically, the PA1 / USART2_RTS port is connected to the 35 port of the main processor, the PA2 / USART2_TX port is connected to the 36 port of the main processor, the PA3 / USART2_RX port is connected to the 37 port of the main processor, and the RESET_ZIGBEE port is connected to the 43 port of the main processor.

[0116] As shown in Figure 16As shown, it is a Zigbee wireless transceiver module circuit schematic diagram, adopts a Zigbee wireless transceiver module based on EFR32MG24B020F1536IM40-B self-research and development, including a wireless system on chip of EFR32MG24B020F1536IM40 model, a quartz crystal resonator of XC21M4-39.00-F10LLDTL model and the like.

[0117] The quartz crystal resonator connects the HFXTAL_I and HFXTAL_O ports of the wireless system on chip, provides a stable frequency signal for the wireless system on chip, the RESETn port is grounded through the capacitor C136, and a low level of an external RESETn can globally reset the Zigbee master chip, the IOVDD port is connected to VDD_3V3_ZIGBEE after filtering capacitors C129 and C130, the AVDD is connected to VDD_3V3_ZIGBEE after filtering capacitors C126 and C127, the DVDD is connected to VDD_3V3_ZIGBEE after filtering capacitor C128, the VREGSW is connected to VDD_3V3_ZIGBEE through filtering capacitors C131 and C132, the RFVDD is connected to VDD_3V3_ZIGBEE after filtering circuit C137 and C138 and L19, and the PAVDD is connected to VDD_3V3_ZIGBEE after filtering circuit composed of capacitors C139 and C140 and inductor L141, to provide a stable and reliable power supply system for the Zigbee master chip.

[0118] The Zigbee wireless transceiver module is a kind of wireless communication module based on Zigbee protocol, mainly used for short distance, low power consumption data transmission. Since the transmission rate of Zigbee is low, the transmission power is only 1mW, and the sleep mode is adopted, the power consumption is low. According to estimation, Zigbee equipment can maintain the use time of 6 months to 2 years or so only by two 5# batteries. The communication delay and the delay of activating from sleep state are very short, the typical search equipment delay is 30ms, the sleep activation delay is 15ms, and the active equipment channel access delay is 15ms, which is suitable for wireless control application with strict delay requirement. The strain data collected by the application is transmitted to the Zigbee wireless transceiver module, the Zigbee wireless transceiver module has a complete Zigbee protocol stack inside, including physical layer, MAC layer, network layer and application layer. The physical layer is responsible for the modulation and demodulation of wireless signal; the MAC layer realizes frame format conversion, data sending and receiving; the network layer handles routing, networking and security tasks; the application layer realizes higher level protocol and application. Finally, the interactive processing of strain data is realized.

[0119] The scheme of the application is tested in practice, and tables 3 to 5 are temperature drift test table, time drift test table and wireless performance test table respectively:

[0120] Table 3. Temperature drift test table of extremely low zero drift strain measurement technology based on Zigbee wireless transmission

[0121] Temperature Strain zero drift -20℃ -0.3με -10℃ -0.2με 0℃ -0.2με 10℃ 0με 20℃ 0με 30℃ 0.1με 40℃ 0.1με 50℃ 0.2με 60℃ 0.2με 70℃ 0.2με 85℃ 0.3με

[0122] Table 4. Time drift test table of extremely low zero drift strain measurement technology based on Zigbee wireless transmission

[0123] Time Strain zero drift 24 hours 0με 48 hours 0με 72 hours 0.1με 96 hours 0.1με 120 hours 0.1με 144 hours 0.1με 168 hours 0.1με

[0124] Table 5. Wireless performance test table of extremely low zero drift strain measurement technology based on Zigbee wireless transmission

[0125] Transmit power Max 20 dBm Communication distance 450 m (visual, open, unobstructed, no interference) Output signal Strain characteristic value: strain average, strain peak, strain effective value, original strain waveform

[0126] According to the test data obtained from the above table, it is known that the application finally realizes that the zero drift only changes by a maximum of 0.6με within the temperature change range of-20℃ to +85℃, the zero drift only changes by a maximum of 0.1με within 1 week of continuous operation, the wireless transmission distance is up to 450m, and information such as strain average value, strain peak value, strain effective value, original strain waveform and the like can be continuously transmitted.

[0127] A large bridge strain monitoring system project of a scientific research unit directly adopts the technical scheme of the application because of many strain measurement points, wiring difficulty, the need to increase measurement points and expand the measurement range in the later period, so that the unit does not need to lay a large number of cables, reduces the cable procurement, laying and later maintenance cost, and significantly reduces the cost. Avoiding the measurement failure and data error caused by cable aging, damage, moisture and the like, the maintenance frequency and difficulty are reduced. In the later period, only wireless measurement nodes need to be added and included in the network, without the need to rewire and large-scale reform the original system, so that the measurement system upgrading and function expansion are facilitated.

[0128] The above only describes the preferred embodiments of the application, and it should be noted that for ordinary skilled persons in the technical field, some improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A strain micro-signal recognition and measurement circuit based on reference power supply self-compensation, characterized by: It includes a Whitten bridge and a strain measurement circuit. The strain gauges form the Whitten bridge. The strain measurement circuit is connected to the Whitten bridge to collect and process strain signals. The strain measurement circuit includes a signal conditioning circuit, a digital processing circuit and a power supply circuit.

2. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 1, characterized in that: The Wheatstone bridge consists of four resistors, each of which is a strain gauge resistor or a component related to a strain gauge resistor.

3. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 2, characterized in that: The signal conditioning circuit includes a common-mode and differential-mode filtering circuit, a resistor-capacitor filtering circuit, and an analog-to-digital converter, and the Wheatstone bridge is connected to the analog converter via the common-mode and differential-mode filtering circuit, the resistor-capacitor filtering circuit, and the analog-to-digital converter. The analog-to-digital converter acquires the output voltage of the Whittenbridge bridge.

4. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 3, characterized in that: The reference voltage is simultaneously connected to the Wheatstone bridge excitation and the reference voltage input of the analog-to-digital converter. The Wheatstone bridge excitation and the reference voltage of the analog-to-digital converter have the same source, and the amplitude change is self-compensated without affecting the measurement accuracy.

5. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 3, characterized in that: The analog-to-digital converter uses an ADS1220IPWR analog-to-digital converter. The AIN1 and AIN2 ports of the analog-to-digital converter collect strain signals. The voltage output end of the Huitongs bridge is connected to the AIN1 and AIN2 ports of the analog-to-digital converter after the interference is filtered out by the common-mode and differential-mode filter circuits.

6. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 1, characterized in that: The digital processing circuit includes a main processor and a memory; the main processor is connected to an analog-to-digital converter to drive the analog-to-digital converter to complete strain signal acquisition; the main processor is connected to a ZIGBEE wireless transceiver module to realize wireless transmission of strain data.

7. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 6, characterized in that: The main processor is STM32F429ZGT6. The SPI4 and SPI5 interfaces of the main processor are connected to several analog-to-digital converters respectively to drive the analog-to-digital converters to complete strain signal acquisition.

8. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 6, characterized in that: It also includes a Zigbee wireless transceiver module. The FSMC interface of the main processor is connected to the memory, and the USART2 interface is connected to the ZIGBEE wireless transceiver module to drive the ZIGBEE wireless transceiver module to realize the wireless transmission of strain data.

9. The strain micro-signal identification and measurement circuit based on reference power supply self-compensation according to claim 1, characterized in that: The power supply circuit includes surge protection circuit, overvoltage, undervoltage, reverse connection protection circuit, common mode and differential mode filter circuit and power conditioning circuit.

10. A method for identifying and measuring strain micro-signals based on reference power supply self-compensation, implemented using the circuit of any one of claims 1 to 9, characterized in that: Each measurement channel uses a low-noise, low-drift, high-precision reference voltage to excite the Wheatstone bridge. This low-noise, low-drift, high-precision reference voltage is simultaneously connected to the Wheatstone bridge excitation and the reference voltage input of the analog-to-digital converter. This not only ensures long-term stability and temperature stability, but also, if the reference chip produces amplitude changes due to external changes, since the Wheatstone bridge excitation and the reference voltage of the analog-to-digital converter are from the same source, the amplitude change can be self-compensated without affecting measurement accuracy.

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