High-sensitivity vibrating wire strain gauge

Abstract

The application discloses a high-sensitivity vibrating wire strain gauge, which comprises a measuring unit, an amplifying unit for amplifying displacement of the measuring unit and a connecting unit for fixing the measuring unit on the amplifying unit, the amplifying unit comprises at least two pulleys and a steel wire wound on the at least two pulleys, the connecting unit has two connecting pieces, and the measuring unit is fixed on the steel wire through the two connecting pieces. The measuring unit of the application is arranged on the steel wire through the connecting unit, so that the effective length of the strain gauge is up to 5m-10m, the strain gauge is particularly suitable for strain monitoring of a large-span bridge, the strain monitoring cost of the bridge is greatly reduced, the self-vibration frequency of the steel wire is amplified, the output signal of the strain gauge is further amplified, the noise caused by the instrument itself is unchanged, the signal strength is enhanced, the signal-to-noise ratio is improved, the error caused by the strain gauge itself is reduced, the sensitivity is improved, the tiny strain of a small crack can be monitored, and more reliable data for evaluating the safety of the bridge is provided.

Description

Technical Field

[0001] This invention relates to strain gauges, and more particularly to a high-sensitivity vibrating wire strain gauge. Background Technology

[0002] Strain gauges, as a type of sensor, are widely used in the construction industry. Their working principle is as follows: when the stress inside the structure being measured changes, the strain gauge synchronously senses the deformation. This deformation is transmitted to the vibrating string through the front and rear end supports, transforming into a change in the string's stress. This changes the string's vibration frequency, and the frequency signal is transmitted via cable to a reading device, allowing the measurement of the strain inside the structure. Currently, strain gauges are commonly used for strain monitoring in buildings and are also applied in monitoring the safety of bridge structures.

[0003] Vibrating wire strain gauges are among the most commonly used strain gauges in the construction industry. While they can meet most monitoring needs, they still have the following shortcomings when used for bridge strain monitoring: First, the measurement range of existing vibrating wire strain gauges is only 250mm. Nowadays, most bridges have spans of tens or even hundreds of meters. If full-bridge monitoring is to be achieved, the number of strain gauges required would be extremely large, greatly increasing the cost of the bridge. Second, due to the short gauge length of vibrating wire strain gauges, their sensitivity is low. If a tiny crack or strain occurs within their measurement range, the signal output by the strain gauge is weak, and the change amplitude of the instrument panel of the strain monitoring system is too small for the human eye to capture the accurate value of the change. This results in the inability to detect tiny cracks, which can eventually lead to damage to the bridge itself.

[0004] In summary, designing a long gauge length strain gauge with long monitoring distance and high accuracy is of great significance for reducing monitoring costs and improving the reliability of monitoring data. Summary of the Invention

[0005] In view of this, the present invention provides a highly sensitive vibrating wire strain gauge that not only has a longer monitoring length but also improves sensitivity, enabling it to monitor minute cracks in bridges and improve bridge safety.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The high-sensitivity vibrating wire strain gauge of the present invention includes a measuring unit, an amplification unit for amplifying the displacement of the measuring unit, and a connecting unit for fixing the measuring unit to the amplification unit. The amplification unit includes at least two pulleys and a steel wire wound on the at least two pulleys. The connecting unit has two connectors, and the measuring unit is fixed to the steel wire by the two connectors.

[0008] In the above-described scheme, the measuring unit of this invention is mounted on a steel wire via a connecting unit, allowing the effective length of the strain gauge to reach 5m to 10m. This makes it particularly suitable for strain monitoring of long-span bridges, significantly reducing the cost of bridge strain monitoring. During measurement, the measuring unit is fixed to the steel wire. When the object being measured experiences strain, at least twice the displacement is transmitted to the measuring unit, thereby amplifying the natural frequency of the steel wire. The tension of the steel wire also increases, leading to an increase in the displacement measured by the strain gauge. This further amplifies the strain gauge's output signal. The noise from the instrument itself remains constant, while the signal strength is enhanced, improving the strain gauge's signal-to-noise ratio, reducing the error inherent in the strain gauge, and increasing its sensitivity. This allows for the detection of minute strains in small cracks, providing more reliable data for assessing bridge safety.

[0009] In a preferred embodiment of the invention, each pulley is connected to an axle via a bearing, and the axle is fixed to the building being monitored to ensure that the pulleys can rotate relative to each other.

[0010] In a more preferred embodiment of the present invention, a bracket is provided on the axle, and the axle is fixed to the monitored building by the bracket, which facilitates fixed installation.

[0011] In a preferred embodiment of the present invention, the measuring unit includes a protective sleeve, a steel wire, and a measuring part fixed between the two connecting members. The steel wire is disposed in a sealed cavity surrounded by the protective sleeve and the connecting members, and both ends of the steel wire are fixedly connected to the connecting members respectively.

[0012] In a preferred embodiment of the present invention, the measuring unit further includes a spring, one end of which is connected to a steel string, and the other end of which is connected to one of the connecting members via a pull rod, wherein the steel string, the spring, and the pull rod are on the same straight line.

[0013] In a preferred embodiment of the present invention, the measuring unit includes a coil, a magnet, and a resin layer sequentially disposed on the protective sleeve from the inside out. The resin layer encapsulates the coil and magnet on the protective sleeve, and the cable leads of the coil extend outward from the resin layer. In actual installation, epoxy resin is used for the resin layer, and the epoxy resin is used to encapsulate the coil and magnet on the protective sleeve, so that the measuring unit and the protective sleeve form a whole.

[0014] In a preferred embodiment of the present invention, the length of the steel wire is greater than 10m, preferably controlled between 10m and 20m. Since the steel wire is wound around two pulleys, the effective length of the strain gauge of the present invention is 5m-10m, to meet the strain monitoring requirements of long-span bridges.

[0015] The working principle of a vibrating wire strain gauge: It characterizes the strain at the point where the strain gauge is located by utilizing the relationship between the natural frequency of the internal steel wire and the change in the wire tension. The initial tension of the steel wire before tensioning.T 0 The corresponding frequency is f 0 Apply tension to the steel string T The vibration frequency of the steel string is f ; tension of steel wire T and frequency f Satisfying the relation ( K (The strain of the strain gauge is a constant). strain displacement change ( EA (where is the axial stiffness of the steel string, and is a constant), and strain... .in, K and EA It is a constant. Therefore, the strain increment changes with frequency. f The frequency increases with the increase of the natural frequency of the steel string. f As the external force increases, the corresponding deformation increment also increases, and the displacement of the strain gauge will also increase.

[0016] Compared to existing vibrating wire strain gauges, this invention fixes the measuring unit on a steel wire, which is wound around two pulleys. During installation, the distance between the two pulleys is 5m-10m, making the gauge length of this invention at least 20 times that of existing strain gauges (based on a 250mm gauge length). This makes it particularly suitable for strain monitoring of long-span bridges, significantly reducing the cost of strain monitoring for such bridges. Taking a 100m long bridge as an example, with a gauge length of 5m-10m, only 10-20 strain gauges are needed to cover the entire bridge; while the effective length of a traditional strain gauge is only 250mm, requiring 200-400 strain gauges to cover a 100m long bridge, 20-40 times more than this invention. Therefore, the strain gauge of this invention significantly reduces the cost of strain monitoring for bridges.

[0017] On the other hand, this invention improves the sensitivity of the strain gauge, enabling it to detect minute strains in the bridge. Specifically: as the working principle of a movable pulley shows, while it cannot change the direction of the force, it can increase the distance. When strain occurs within the monitored length of the bridge, the pulley moves by one-fold deformation, the steel wire increases its displacement by two-fold, and this displacement is then transmitted to the spring by two-fold deformation. The spring then transmits two-fold deformation to the steel string, the coil excites the steel string, and the change in spring force causes the steel string's natural frequency to change. f The increase in frequency results in a relative increase in the frequency of the steel wire monitored by the coil, which in turn increases the displacement Δ measured by the strain gauge. lThis also increases the output signal. Since the noise from the instrument itself remains constant, the enhanced signal strength improves the strain gauge's signal-to-noise ratio and sensitivity. Therefore, the strain gauge of this invention can monitor minute strains in bridges, and consequently detect tiny cracks, providing more reliable data for bridge safety assessment. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

[0019] Figure 2 yes Figure 1 Enlarged view of the measurement unit. Detailed Implementation

[0020] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0021] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] This invention provides a highly sensitive vibrating wire strain gauge. On one hand, it expands the effective length of the strain gauge by N times (N≥20), greatly reducing the number of strain gauges required for bridge strain monitoring and lowering the cost of bridge strain monitoring. The cost of the strain gauge is only one-twentieth of that of existing strain gauges, making it particularly suitable for long-span bridges. On the other hand, this invention amplifies the natural frequency of the steel wire, further amplifying the output signal of the strain gauge and improving its sensitivity, enabling the detection of strain in minute cracks.

[0023] like Figure 1-2 As shown, the high-sensitivity vibrating wire strain gauge of the present invention includes a measuring unit 1, an amplification unit for amplifying the displacement of the measuring unit 1, and a connecting unit for fixing the measuring unit 1 to the amplification unit. The amplification unit includes two pulleys 2.1 and a steel wire 2.2 wound on the two pulleys 2.1. The connecting unit has two connectors, and the measuring unit 1 is fixed to the steel wire 2.2 by the two connectors.

[0024] During actual installation, the circumferential surface of pulley 2.1 has a groove, and steel wire 2.2 is wound inside the groove. During installation, steel wire 2.2 should be taut but without tension. Additionally, each pulley 2.1 is connected to an axle via a bearing, allowing the pulleys 2.1 to rotate relative to each other. A bracket 2.3 is mounted on the axle, and the axle is fixed to the monitored bridge via the bracket 2.3. The two pulleys 2.1 are indirectly mounted on the bridge using the bracket 2.3, simplifying the installation process.

[0025] Combination Figure 2 It can be seen that the connecting component is the connecting flange 3; the measuring unit 1 includes a protective sleeve 1.1, a steel wire 1.2, and a measuring part. The two ends of the protective sleeve 1.1 are sealed and inserted into the grooves of the connecting flange 3. The protective sleeve 1.1 and the two connecting flanges 3 form a sealed chamber to protect the steel wire 1.2. One end of the steel wire 1.2 is fixed to one of the connecting flanges 3, and the other end of the steel wire 1.2 is fixed with a spring 1.3. The spring 1.3 is fixed to the other connecting flange 3 through a tie rod 1.4, and the steel wire 1.2, the spring 1.3, and the tie rod 1.4 are arranged in a straight line. The measuring unit includes, from the inside out, a coil 1.5, a magnet 1.6 (the magnet 1.6 is mounted on the coil 1.5 and is made of a thin permanent magnet material), and a resin layer 1.7 (using encapsulating resin, preferably epoxy resin) arranged sequentially on the protective sleeve 1.1. The encapsulating resin encapsulates the coil 1.5 and magnet 1.6 onto the protective sleeve 1.1, forming an integrated structure for the measuring unit. The cable lead 1.8 of the coil 1.5 (one end of the cable lead 1.8 is connected to the core wire of the coil 1.5 via a disconnect connector) is led outwards through the resin layer 1.7. When the spring 1.3 deforms and tensions, it can cause the steel string 1.2 to tighten. High-frequency vibration of the steel string 1.2 can be achieved by exciting the coil 1.5.

[0026] The installation process of this invention is as follows: one end of the steel wire 2.2 is fixed to one of the connecting flanges 3, and the other end of the steel wire 2.2 is fixed to another connecting flange 3. The total length of the steel wire 2.2 is more than 10m. Then, the steel wire 2.2 is wound in the groove of the two pulleys 2.1. The pulleys 2.1 are installed on the bridge to be monitored using the bracket 2.3 and bolts, so that the steel wire 2.2 is in a taut and tension-free state. The cable lead 1.8 is connected to the strain monitoring system of the bridge.

[0027] The working principle of this invention is as follows: When the bridge shifts, the displacement is transmitted to the spring 1.3 via two pulleys 2.1 anchored to the bridge. The spring 1.3 then acts directly on the steel string 1.2. As can be seen from the working principle of the movable pulley 2.1, it cannot change the direction of the force, but it can increase the distance. Therefore, when the pulley 2.1 moves by one unit of deformation, the steel wire 2.2 of this invention can increase its displacement by two units, which is then transmitted to the spring 1.3 by two units of deformation. This two units of deformation are then transmitted to the steel string 1.2 via the spring 1.3. The coil 1.5 excites the steel string 1.2, and the change in the elastic force of the spring 1.3 causes the natural frequency of the steel string 1.2 to change. f As the frequency of the steel wire 1.2 monitored by coil 1.5 increases, the displacement measured by the strain gauge also increases.

[0028] According to the strain formula It can be seen that when the gauge length l When constant, the Δ transmitted to the strain gauge l If the signal strength increases, the strain gauge will amplify its output signal. Since the noise from the instrument itself remains constant, the increased signal strength improves the strain gauge's signal-to-noise ratio and sensitivity. This allows the strain gauge to detect strain caused by small cracks in the bridge, thus providing more reliable data for bridge safety assessment.

[0029] Furthermore, the steel wire 2.2 can be as long as 10m (or even 20m), while the effective length of the strain gauge of this invention is at least 5m (approximately half the length of the steel wire 2.2), making it particularly suitable for strain monitoring of long-span bridges and significantly reducing the cost of strain monitoring for such bridges. Taking a 100m long bridge as an example, the effective length of this invention can reach 5m-10m, requiring only 10-20 strain gauges to cover the entire bridge; whereas the effective length of traditional strain gauges is only 250mm, requiring 200-400 strain gauges to cover a 100m long bridge, which is 20-40 times that of this invention. This invention significantly reduces the cost of strain monitoring for bridges.

[0030] Finally, it should be emphasized that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some of the technical features. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-sensitivity vibrating-wire strain gauge comprising a measuring cell, characterized in that: It also includes an amplification unit for amplifying the displacement of the measuring unit and a connecting unit for fixing the measuring unit to the amplification unit. The amplification unit includes at least two pulleys and a steel wire wound on the at least two pulleys. The connecting unit has two connectors. The measuring unit is fixed to the steel wire by the two connectors. The length of the steel wire is greater than 10m. Each of the pulleys is connected to an axle via a bearing, and the axle is fixed to the building being monitored; The measuring unit includes a protective sleeve, a steel wire, and a measuring part fixed between two connecting parts. The steel wire is arranged in a sealed cavity surrounded by the protective sleeve and the connecting parts, and both ends of the steel wire are fixedly connected to the connecting parts respectively. The measuring unit also includes a spring, one end of which is connected to the steel wire, and the other end is connected to one of the connecting parts through a pull rod. The steel wire, the spring, and the pull rod are on the same straight line. When the pulley moves by one time the deformation, the steel wire increases the displacement by two times, and the spring transmits two times the deformation to the steel wire.

2. The high-sensitivity vibrating wire strain gauge according to claim 1, characterized in that: The axle is equipped with a bracket, and the axle is fixed to the building being monitored by the bracket.

3. The high-sensitivity vibrating wire strain gauge of claim 1, wherein: The measuring unit also includes a coil, a magnet, and a resin layer arranged sequentially from the inside to the outside on the protective sleeve. The resin layer encapsulates the coil and magnet on the protective sleeve, and the cable lead of the coil extends outward from the resin layer.

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