A kind of nickel-titanium shape memory alloy resistance strain gauge for bridge strain monitoring
By employing NiTi shape memory alloy wire and a double-layer encapsulation structure for bridge strain gauges, combined with a four-wire resistance measurement circuit and redundant design, the sensitivity and environmental adaptability issues of existing bridge strain monitoring devices have been resolved, achieving high-precision and long-life bridge structural health monitoring.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- CHINA CONSTR SEVENTH ENG DIVISION CORP LTD
- Filing Date
- 2025-08-27
- Publication Date
- 2026-07-03
AI Technical Summary
Existing bridge strain monitoring devices suffer from low sensitivity, poor environmental adaptability, and insufficient durability. In particular, they are prone to signal attenuation, breakage, and measurement errors in complex environments, making it difficult to meet the requirements for long-term stable monitoring.
Using NiTi shape memory alloy wire as the sensing element, combined with cold-pressed terminal fixing process and double-layer packaging structure, it is equipped with a four-wire resistance measurement circuit, a 24-bit analog-to-digital converter and PT1000 temperature sensor to achieve high sensitivity and fatigue resistance. It also eliminates errors through redundant design and differential amplification technology to ensure data accuracy.
It achieves high-precision and long-life bridge strain monitoring, can work stably in a wide temperature range and complex environment, reduces failure rate, and ensures the continuity and accuracy of monitoring data.
Smart Images
Figure CN224455690U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of bridge strain monitoring technology, and relates to a nickel-titanium shape memory alloy resistance strain gauge for bridge strain monitoring. Background Technology
[0002] In the field of bridge structural health monitoring, existing strain monitoring devices generally use foil strain gauges or fiber optic sensors, but both have significant technical drawbacks: foil strain gauges have low sensitivity (sensitivity coefficient GF≈2.0), and are prone to measurement failure due to metal fatigue after long-term use; while fiber optic sensors have high sensitivity, they have poor corrosion resistance and are prone to signal attenuation or breakage in complex environments such as salt spray and humidity on bridges. Meanwhile, traditional packaging processes often use a single-layer structure, which can lead to cracking of the packaging layer due to differences in the thermal expansion coefficients of materials within a wide temperature range of -40℃ to 150℃, severely affecting sensor durability; in two-wire measurement circuits, the lead resistance introduces significant measurement errors during long-distance transmission, and discrete temperature compensation schemes cannot accurately eliminate the nonlinear resistance changes generated during the phase transformation of nickel-titanium (NiTi) shape memory alloys, resulting in distorted monitoring data. Furthermore, existing sensing elements are mostly single-wire structures, lacking redundancy design and without a strain-free reference section, making it difficult to calibrate baseline drift and failing to meet the requirements for long-term stable monitoring of bridges. Therefore, there is an urgent need to develop a new strain monitoring device that combines high sensitivity, strong environmental adaptability, and high reliability to improve the accuracy and stability of bridge structural health monitoring. Utility Model Content
[0003] The purpose of this invention is to solve the problems of insufficient sensitivity and environmental adaptability of strain gauges in the prior art, and to provide a nickel-titanium shape memory alloy resistance strain gauge for bridge strain monitoring.
[0004] To achieve the above objectives, the present invention adopts the following technical solution:
[0005] A nickel-titanium shape memory alloy resistance strain gauge for bridge strain monitoring includes:
[0006] The sensing element is made of NiTi shape memory alloy wire, and the two ends of the NiTi shape memory alloy wire are fixedly electrically connected by cold-pressed terminals;
[0007] The encapsulation structure covers the outside of the sensing element. The encapsulation structure is a double-layer structure, with an inner layer of high-temperature resistant silicone tube and an outer layer of stainless steel braided mesh. The end of the encapsulation structure is equipped with an IP68-level sealed waterproof connector.
[0008] The resistance measurement circuit is electrically connected to the cold-pressed terminal. The resistance measurement circuit adopts a four-wire measurement layout and integrates a constant current source, a differential amplifier, a 24-bit analog-to-digital converter, and a PT1000 temperature sensor for temperature compensation.
[0009] The data acquisition and communication module is connected to the output terminal of the resistance measurement circuit and is used to receive strain data and transmit it in real time.
[0010] The NiTi shape memory alloy wire is arranged in a pre-stretched straight or zigzag pattern inside the high-temperature resistant silicone tube.
[0011] The cold-pressed terminal is made of copper or gold-plated, and it is firmly electrically and mechanically connected to the NiTi shape memory alloy wire by hydraulic clamping.
[0012] The stainless steel woven mesh and the metal shell of the IP68-rated waterproof joint are sealed and fixed together by laser welding or interference fit.
[0013] The inner high-temperature resistant silicone tube of the encapsulation structure has a thickness of 1.5mm ± 0.2mm, the outer stainless steel braided mesh has a mesh count of 200, and the end of the outer encapsulation structure is fully sealed and protected by an IP68-level waterproof joint.
[0014] The NiTi shape memory alloy wire of the sensing element has a diameter of 0.3mm ± 0.05mm, a phase transition temperature range of -10℃ to 40℃, and an insulating layer with a thickness of 0.1μm is plated on the surface of the alloy wire.
[0015] In the four-wire layout of the resistance measurement circuit, the constant current source output current is 1mA±0.1%, the differential amplifier gain is adjustable from 100 to 1000 times, the 24-bit analog-to-digital converter sampling rate is not less than 1kHz, and the thermal coupling time difference between the PT1000 temperature sensor and the NiTi sensing element is ≤0.5s.
[0016] The sensing element is provided with a strain-free reference section, the length of which is 10%-15% of the total length of the sensing element. The reference section is isolated from the monitoring surface by an insulating sleeve.
[0017] The PT1000 temperature sensor is mounted on the PCB board of the resistance measurement circuit and is located near the input terminal connected to the sensing element.
[0018] The strain gauge is equipped with a redundant design module, which includes two NiTi shape memory alloy wires connected in parallel.
[0019] Compared with the prior art, the present invention has the following beneficial effects:
[0020] This invention discloses a nickel-titanium shape memory alloy resistance strain gauge for bridge strain monitoring. By employing NiTi shape memory alloy wire as the core sensing element, combined with cold-pressed terminal fixing technology and a double-layer protective packaging structure, it significantly improves the environmental adaptability of the device while ensuring the high sensitivity and fatigue resistance of the sensing element. The four-wire resistance measurement circuit integrates a 24-bit high-precision ADC and differential amplification technology, and with the real-time compensation function of the PT1000 temperature sensor, it effectively eliminates the influence of lead resistance error and temperature drift, providing a comprehensive solution with high precision, long life and strong adaptability for the health monitoring of large bridge structures. Attached Figure Description
[0021] To more clearly illustrate the technical solutions of the embodiments of this utility model, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this utility model and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0022] Figure 1 This is a modular structure diagram of the present invention;
[0023] Figure 2 This is a schematic diagram of a Wheatstone bridge. Detailed Implementation
[0024] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0025] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0026] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0027] The present invention will now be described in further detail with reference to the accompanying drawings:
[0028] See Figure 1 The diagram shows the modular structure of this utility model. A nickel-titanium shape memory alloy resistance strain gauge for bridge strain monitoring, as described in this utility model, includes:
[0029] The sensing element is composed of NiTi shape memory alloy wire, with both ends of the NiTi shape memory alloy wire electrically connected and fixed by cold-pressed terminals. The diameter of the NiTi shape memory alloy wire in the sensing element is 0.3mm ± 0.05mm, the phase transition temperature range is -10℃ to 40℃, and the surface of the alloy wire is plated with an insulating layer with a thickness of 0.1μm. The cold-pressed terminals are copper or gold-plated terminals, which are firmly electrically and mechanically connected to the NiTi shape memory alloy wire by hydraulic clamping. Using NiTi shape memory alloy wire as the sensing element, its hyperelastic properties can capture micro-strain level deformation. Combined with the cold-pressed terminal fixing process, it avoids the metal fatigue problems caused by traditional welding, extending the service life to more than 10 years.
[0030] The sensing element is provided with a strain-free reference section, the length of which is 10%-15% of the total length of the sensing element. The reference section is isolated from the monitoring surface by an insulating sleeve.
[0031] An encapsulation structure, covering the outside of the sensing element, is a double-layer structure. The inner layer is a high-temperature resistant silicone tube, and the outer layer is a stainless steel braided mesh. The end of the encapsulation structure is equipped with an IP68-rated waterproof joint. The inner high-temperature resistant silicone tube of the double-layer encapsulation structure has a thickness of 1.5mm ± 0.2mm, and the outer stainless steel braided mesh has a mesh count of 200. The end of the outer encapsulation structure achieves full sealing protection through the IP68-rated waterproof joint. The stainless steel braided mesh and the metal shell of the IP68-rated waterproof joint are sealed and fixed together by laser welding or interference fitting. The NiTi shape memory alloy wire is arranged in a pre-stretched straight or zigzag pattern inside the high-temperature resistant silicone tube.
[0032] In the dual-layer encapsulation structure, the inner high-temperature resistant silicone tube and the outer stainless steel braided mesh work together, along with IP68 waterproof connectors, to ensure that the device works stably in the complex environment of bridges, and the encapsulation layer does not crack within a temperature range of -40℃ to 150℃.
[0033] A resistance measurement circuit is electrically connected to the cold-pressed terminal. This circuit employs a four-wire measurement layout and integrates a constant current source, a differential amplifier, a 24-bit analog-to-digital converter (ADC), and a PT1000 temperature sensor for temperature compensation. In this four-wire layout, the constant current source outputs 1mA ± 0.1%, the differential amplifier gain is adjustable from 100 to 1000 times, the 24-bit ADC sampling rate is not less than 1kHz, and the thermal coupling time difference between the PT1000 temperature sensor and the NiTi sensing element is ≤0.5s. The PT1000 temperature sensor is mounted on the PCB board of the resistance measurement circuit, close to the input terminal connected to the sensing element.
[0034] The four-wire resistance measurement circuit eliminates lead resistance errors by separating the excitation line from the measurement line. Combined with a 24-bit analog-to-digital converter and a differential amplifier, it achieves a resistance resolution of 0.001%, meeting the requirements for dynamic strain monitoring of bridges.
[0035] The data acquisition and communication module is connected to the output terminal of the resistance measurement circuit and is used to receive strain data and transmit it in real time.
[0036] The strain gauge is equipped with a redundant design module, which includes two NiTi shape memory alloy wires connected in parallel. The parallel dual NiTi sensing element structure maintains ≥80% measurement accuracy even when a single wire breaks. Combined with the breakpoint resume function of the data acquisition module, it ensures the continuity of bridge monitoring data.
[0037] The NiTi shape memory alloy wire used in this invention can be used to establish a simple strain sensing model using three parameters: resistance change rate ΔR / R, temperature T, and strain α.
[0038]
[0039] like Figure 2 The diagram shows the schematic of a Wheatstone bridge. The strain gauges R0, R1, and R2, and the resistor RX to be measured are connected in a quadrilateral, with each side called an arm of the bridge. A power supply E is connected between diagonals A and C, and a galvanometer G is connected between diagonals B and D. Therefore, the bridge consists of four arms, a power supply, and galvanometers. When switch K... E and K G After connection, current flows through each branch, and the galvanometer branch acts as a connector between branches ABC and ADC. By appropriately adjusting the values of R0, R1, and R2, no current can flow through the bridge, i.e., the current through the galvanometer IG = 0. At this point, the potentials at points B and D are equal. This state of the bridge is called a balanced state. The resistance to be measured is R. X It equals the product of R1 / R2 and R0, that is:
[0040]
[0041] The nickel-titanium shape memory alloy resistance strain gauge provided by this utility model uses NiTi shape memory alloy wire as the sensing element and combines it with cold-pressed terminal fixing technology. This ensures a micro-strain detection sensitivity of 0.1με level while extending the service life to over 10 years. The double-layer encapsulation structure, through composite protection of high-temperature resistant silicone tubing and stainless steel braided mesh, along with IP68 waterproof connectors, ensures stable operation in a wide temperature range of -40℃ to 150℃ and high humidity environments. The four-wire resistance measurement circuit integrates a 24-bit high-precision ADC and differential amplification technology, eliminating lead resistance errors and achieving a resistance resolution of 0.001%, with a sampling rate exceeding 1kHz. The thermal coupling design of the PT1000 temperature sensor and NiTi element, combined with a real-time nonlinear compensation algorithm, controls the temperature error within ±0.1℃. The parallel dual-sensor structure and the breakpoint resume communication module together form a redundant system, reducing the failure rate to below 0.5% / year. The combination of a stainless steel shielding layer and differential signal transmission technology effectively suppresses electromagnetic interference in the bridge environment, ensuring a signal-to-noise ratio ≥70dB. This device provides a comprehensive solution for bridge structural health monitoring that combines high precision, long lifespan, and environmental adaptability through the synergistic optimization of materials science, circuit design, and structural engineering.
[0042] The above are merely preferred embodiments of this utility model and are not intended to limit the scope of this utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this utility model should be included within the protection scope of this utility model.
Claims
1. A nickel-titanium shape memory alloy electrical resistance strain gauge for bridge strain monitoring, characterized in that, include: The sensing element is made of NiTi shape memory alloy wire, and the two ends of the NiTi shape memory alloy wire are fixedly electrically connected by cold-pressed terminals; The encapsulation structure covers the outside of the sensing element. The encapsulation structure is a double-layer structure, with an inner layer of high-temperature resistant silicone tube and an outer layer of stainless steel braided mesh. The end of the encapsulation structure is equipped with an IP68-level sealed waterproof connector. The resistance measurement circuit is electrically connected to the cold-pressed terminal. The resistance measurement circuit adopts a four-wire measurement layout and integrates a constant current source, a differential amplifier, a 24-bit analog-to-digital converter, and a PT1000 temperature sensor for temperature compensation. The data acquisition and communication module is connected to the output terminal of the resistance measurement circuit and is used to receive strain data and transmit it in real time.
2. A nickel-titanium shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, wherein, The NiTi shape memory alloy wire is arranged in a pre-stretched straight or zigzag pattern inside the high-temperature resistant silicone tube.
3. A NiTi shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, characterized in that, The cold-pressed terminal is made of copper or gold-plated, and it is firmly electrically and mechanically connected to the NiTi shape memory alloy wire by hydraulic clamping.
4. A NiTi shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, characterized in that, The stainless steel woven mesh and the metal shell of the IP68-rated waterproof joint are sealed and fixed together by laser welding or interference fit.
5. A NiTi shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, wherein, The inner high-temperature resistant silicone tube of the encapsulation structure has a thickness of 1.5mm ± 0.2mm, the outer stainless steel braided mesh has a mesh count of 200, and the end of the outer encapsulation structure is fully sealed and protected by an IP68-level waterproof joint.
6. The nickel-titanium shape memory alloy resistance strain gauge for bridge strain monitoring as described in claim 1, characterized in that, The NiTi shape memory alloy wire of the sensing element has a diameter of 0.3mm ± 0.05mm, a phase transition temperature range of -10℃ to 40℃, and an insulating layer with a thickness of 0.1μm is plated on the surface of the alloy wire.
7. A NiTi shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, wherein, In the four-wire layout of the resistance measurement circuit, the constant current source output current is 1mA±0.1%, the differential amplifier gain is adjustable from 100 to 1000 times, the 24-bit analog-to-digital converter sampling rate is not less than 1kHz, and the thermal coupling time difference between the PT1000 temperature sensor and the NiTi sensing element is ≤0.5s.
8. A nickel-titanium shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, wherein, The sensing element is provided with a strain-free reference section, the length of which is 10%-15% of the total length of the sensing element. The reference section is isolated from the monitoring surface by an insulating sleeve.
9. A NiTi shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, characterized in that, The PT1000 temperature sensor is mounted on the PCB board of the resistance measurement circuit and is located near the input terminal connected to the sensing element.
10. A NiTi shape memory alloy electrical resistance strain gauge for bridge strain monitoring according to claim 1, characterized in that, The strain gauge is equipped with a redundant design module, which includes two NiTi shape memory alloy wires connected in parallel.