CN206311247U - A kind of sensor device of power and displacement measurement based on distributed fibre optic sensing - Google Patents

Abstract

The utility model discloses a sensor device for force and displacement measurement based on distributed optical fiber sensing. The distributed strain sensing optical fiber is glued to the side wall of the thin-walled metal ring with epoxy resin glue along the entire length; the optical fiber demodulator and the distributed strain sensing optical fiber pasted on the side wall of the thin-walled metal ring The signal transmission optical fiber is connected in series with each other, and connected to the computer through the serial port and the network cable; after the force or displacement is applied to the apex of the thin-walled metal ring, the optical fiber demodulation equipment and computer are used to collect and record the thin-walled metal ring under loading. The circumferential strain distribution of the thin-walled metal ring is smoothed by the moving average method, and the trigonometric function is fitted to obtain the maximum circumferential strain value of the thin-walled metal ring, so as to calculate the force and displacement; through the calibration test Obtain the linear relationship between the strain value and the force at the apex of the thin-walled metal ring and the corresponding displacement, and on this basis obtain the calibration coefficient of the sensor.

Description

A sensor device for force and displacement measurement based on distributed fiber optic sensing

technical field

The utility model belongs to the technical field of optical fiber sensors, in particular to a sensor device for force and displacement measurement based on distributed optical fiber sensing.

Background technique

Thin-walled metal rings have been widely used as force sensors in traditional geotechnical testing instruments, such as unconfined compressive strength testers, triaxial instruments, and direct shear instruments. These instruments measure the force by reading the deformation of the ring under load through dial indicators and dial gauges. But in most cases, this method has low measurement accuracy, small range, and requires regular calibration. Another method is to attach the strain gauge to the metal ring with an adhesive to form a Wheatstone bridge, and then convert the resistance change caused by the strain into a voltage signal. The defect of this method is that the test reading is susceptible to electromagnetic interference and the reading is inaccurate. Due to the poor reliability of force and displacement measurement, the development of geotechnical testing instruments is seriously hindered.

In recent years, distributed optical fiber sensing technology has been developed by leaps and bounds. This technology can quickly collect optical signals at any position of the optical fiber, and combined with relevant sensing principles, it can obtain physical parameters such as strain and temperature at all positions along the entire length of the optical fiber, realizing distributed monitoring that is difficult to achieve with conventional monitoring technologies. In addition, this technology has the characteristics of large data volume, no electromagnetic interference, fully automatic, and remote monitoring. Because of these advantages, distributed optical fiber monitoring technology is increasingly used in various engineering structure monitoring and indoor experiments.

The principle of Brillouin optical time-domain analysis/reflection technology (BOTDA/R) is to use the linear relationship between the frequency change (frequency shift) of the Brillouin scattered light in the optical fiber and the axial strain of the optical fiber or the ambient temperature to achieve Sensing, the relationship can be expressed as:

In the formula: ν _B (ε, T), ν _B (ε ₀ , T ₀ ) are the frequency shifts of the Brillouin scattered light in the optical fiber before and after the measurement, respectively; ε, ε ₀ are the axial strain before and after the test, respectively ; T, T ₀ are the temperature values before and after the test respectively. Scale factor with The values are 0.05MHz/με and 1.2MHz/℃, respectively.

Contents of the invention

The purpose of this utility model is to provide a sensor device for force and displacement measurement based on distributed optical fiber sensing, so that the force and displacement data measured by the geotechnical test are more accurate and reliable, and realize automatic measurement, thereby completely solving the problem of Existing geotechnical testing instruments have defects such as low force and displacement measurement accuracy and electromagnetic interference.

In order to solve the above problems, the utility model adopts the following technical solutions: a sensor device based on distributed optical fiber sensing force and displacement measurement, mainly including distributed strain sensing optical fiber, thin-walled ring, signal transmission optical fiber, optical fiber demodulation equipment and a computer; the distributed strain sensing optical fiber is connected in series with the optical fiber demodulation device through the signal transmission optical fiber, and the computer and the optical fiber demodulation device are connected by a serial port and a network cable; the distributed strain sensing optical fiber is pasted on the side wall of the thin-walled ring .

The whole distributed strain sensing optical fiber is pasted and fixed on the side wall of the thin-walled ring along the whole length.

The distributed strain sensing optical fiber and the signal transmission optical fiber are fused to each other, and a heat-shrinkable sleeve is covered at the fused joint.

Beneficial effect:

(1) According to mechanical analysis, there is an ideal linear relationship between the force and displacement at the apex of the thin-walled ring and the maximum circumferential strain, thus obtaining the calibration coefficients K ₁ and K ₂ ;

(2) A force and displacement measurement method based on distributed optical fiber sensing is proposed to achieve high-precision, fully automatic, and distributed testing of thin-walled ring deformation, which overcomes the low efficiency, large error, and small amount of monitoring data of traditional methods. question;

(3) The utility model has the advantages of simple installation, accurate measurement, high degree of automation and good cost performance.

Description of drawings

Fig. 1 is a structural representation of the utility model;

Fig. 2 is a schematic diagram of a sensor test device for distributed optical fiber force measurement and displacement in an embodiment; wherein, 1 is a distributed strain sensing optical fiber, 2 is a thin-walled ring, 3 is a signal transmission optical fiber, 4 is a computer, and 5 is an optical fiber demodulation device , 6 is a universal testing machine.

Fig. 3 is the optical fiber strain reading and fitting figure in the utility model embodiment;

Fig. 4-5 is the comparison between the theoretical calculation and the actual measured value in the utility model embodiment;

detailed description

The technical solution of the utility model will be described in more detail below in conjunction with the accompanying drawings and embodiments.

A distributed optical fiber force sensor includes distributed strain sensing optical fiber, thin-walled ring, signal transmission optical fiber, optical fiber demodulation equipment and computer. The optical fiber demodulation equipment and the distributed strain sensing optical fiber pasted on the side wall (inner wall or outer wall) of the thin-walled ring are connected in series through the signal transmission optical fiber, and the computer and the optical fiber demodulation equipment are connected by serial ports and network cables.

As a further optimization of the above solution, the thin-walled ring is made of a metal material with a linear elastic stress-strain relationship.

As a further optimization of the above scheme, in order to ensure that the deformation of the optical fiber and the metal ring is consistent, the entire distributed strain sensing optical fiber is tightly adhered to the side wall of the thin-walled ring with epoxy resin along the entire length, and Place it indoors for 24 hours to make it stick firmly to the ring. Since the optical fiber is relatively soft, only the full-length bonding method can ensure that the optical fiber is evenly adhered to the side wall of the thin-walled ring. Using methods such as binding and fixed-point bonding will cause measurement errors.

As a further optimization of the above solution, the distributed strain sensing optical fiber and the signal transmission optical fiber are fused to each other, and a heat shrinkable sleeve is used to protect the fused joint.

In the above scheme, a force or displacement is applied at the apex of the thin-walled ring, so that the distributed strain sensing optical fiber pasted on the side wall of the thin-walled ring is strained, and the thin-walled ring is collected and recorded by an optical fiber demodulation device and a computer. The hoop strain value of ;

Further, the moving average method is used to smooth the strain monitoring data. The smoothed strain data conforms to the characteristics of trigonometric functions, and is fitted in the form of cosine function ε(x)=acos[b(xc)]+d, where : The parameter a=|ε| _max represents the maximum hoop strain value obtained by fitting, the parameter b is used to eliminate the periodic error of the function, the parameter c is used to eliminate the eccentric error existing in loading, and the parameter d is used to eliminate the temperature change Error, x means ε (x) means the hoop strain value of the thin-walled ring under a certain load and displacement. On the one hand, the fitting function can well reflect the strain curve characteristics of the thin-walled ring, and on the other hand, because the fitting method can eliminate various errors in the test and improve the test accuracy. According to the fitting equation, the maximum hoop strain value |ε| _max of the thin-walled ring under a certain load and displacement is obtained;

Further, according to F=K ₁ ×|ε| _max and ΔD=K ₂ ×|ε| _max , the force at the apex of the thin-walled ring and the corresponding displacement can be obtained from the maximum circumferential strain value, where: F represents The force acting on the thin-walled ring; ΔD represents the displacement at the apex of the thin-walled ring; K ₁ and K ₂ are constants, determined through calibration tests. In the above scheme, it is known through theoretical formula derivation that the above-mentioned linear relationship exists between the force and displacement at the vertex of the thin-walled ring and the maximum circumferential strain of the thin-walled ring.

Further, in order to obtain the calibration coefficients K ₁ and K ₂ , the thin-walled circular ring pasted with the distributed strain sensing optical fiber is placed on the loading platform, and the distributed strain sensing optical fiber is connected to the optical fiber demodulation device with a signal transmission optical fiber, The optical fiber demodulation equipment is connected to the computer; a known force and displacement are applied to the apex of the thin-walled ring, so that the distributed strain sensing optical fiber pasted on the side wall of the thin-walled ring is strained, and the optical fiber demodulation equipment, computer acquisition, Record the circumferential strain measurement value of the thin-walled ring; use the moving average method to smooth the strain data, and use the cosine function to fit. According to the fitting equation, the maximum hoop strain value of the thin-walled ring under a certain load is obtained; by changing the force and displacement applied to the thin-walled ring, the maximum hoop strain value of the thin-walled ring under different forces and displacements is obtained. Calculate the calibration coefficients K ₁ and K ₂ according to the formulas F=K ₁ ×|ε| _max and ΔD=K ₂ ×|ε| _max .

The principle of the utility model: use the distributed strain sensing optical fiber pasted on the thin-walled circular ring to measure the circumferential strain of the circular ring under the action of external force; collect the strain value of the distributed strain sensing optical fiber through the optical fiber demodulation equipment and computer ; Smooth and fit the collected strain data to obtain the maximum hoop strain value of the thin-walled ring; calculate the force and displacement according to the linear relationship between the force at the apex of the thin-walled ring and the corresponding displacement and the maximum hoop strain value.

Example 1

As shown in Fig. 2, a distributed optical fiber force measurement and displacement sensor includes a distributed strain sensing optical fiber 1, a thin-walled ring 2, a signal transmission optical fiber 3, a computer 4, an optical fiber demodulation device 5, and a universal testing machine 6. In the method, in order to ensure that the deformation of the optical fiber and the metal ring are consistent, the distributed strain sensing optical fiber 1 is glued to the outer wall of the thin-walled ring 2 with glue such as epoxy resin, and placed in the room for 24 hours, so that it is consistent with the thin-walled ring 2. The surface of ring 2 is adhered firmly. The optical fiber demodulation device 5 is connected in series with the distributed strain sensing optical fiber 1 pasted on the side wall of the thin-walled ring 2 through the signal transmission optical fiber 3 . The joints of the distributed strain sensing optical fiber 1 and the signal transmission optical fiber 3 are protected by a heat shrinkable sleeve. The readings of the distributed strain sensing optical fiber 1 are automatically collected through the optical fiber demodulation device 5 and the computer 4 . The optical fiber used in the embodiment is a single-mode single-core tight-packed optical fiber with a diameter of 0.9 mm.

The device is loaded on the universal testing machine 6 using a uniform displacement loading method, and the display on the universal testing machine 6 records the force and displacement relationship curve in the loading process, and the measured value is used to verify the force calculated by the optical fiber strain, Accuracy of displacement.

When the apex of the thin-walled ring 2 is subjected to force, the distributed sensing optical fiber 1 pasted on the side wall of the thin-walled ring 2 will be strained, and the strain will cause the frequency of Brillouin scattered light on the distributed strain sensing fiber to occur The optical fiber demodulation equipment can measure the frequency shift in real time, so as to obtain the hoop strain distribution of the metal ring. In order to eliminate measurement errors, the measured strain data are smoothed by moving average method.

The thin-walled ring undergoes elliptical deformation under radial force, and the radial displacement of each point on the thin-walled ring is:

In the formula: y is the radial displacement of each point on the thin-walled ring, is the azimuth angle, and ΔD is the change in diameter. In addition, according to the theory of mechanics, there is the following relationship between the radial displacement and the bending moment of each point on the thin-walled ring:

In the formula: is the bending moment of the thin-walled ring, E is the elastic modulus of the thin-walled ring, I is the moment of inertia of the thin-walled ring, and R is the radius of the thin-walled ring. Obtained from the above formula: when =90°, the maximum hoop strain of the thin-walled ring is This formula can be rewritten as In the formula: K ₂ is the calibration coefficient of the displacement, and D is the diameter of the thin-walled ring. According to Timoshenko's thin-walled ring stress calculation formula in elastic mechanics, the formula for the ring strain ε of the inner and outer walls of the thin-walled ring under the action of a certain radial force can be obtained

In the formula: ω is the thickness of the thin-walled ring, δ is the width of the thin-walled ring, F is the radial force in two opposite directions on the thin-walled ring per unit thickness, θ is the azimuth angle, R _a is the center of the metal ring The diameter E is the elastic modulus of the thin-walled ring. When θ=90°, the absolute value of the thin-walled circular strain reaches the maximum value, and is further converted to In the formula: K ₁ is the calibration coefficient of the force.

The implementation of the calibration test includes: using a loading device to apply a radial force in the opposite direction to the metal ring, and record the hoop strain reading of the thin-walled ring after the reading is stable, and then load step by step, and record the strain data in sequence.

The moving average method of the measured strain readings is used to smooth the data, and the thin-walled circular ring strain readings obtained by the smoothing processing are fitted in the form of cosine function ε(x)=acos[b(xc)]+d, the formula Middle: parameter a=|ε| _max represents the maximum hoop strain value obtained by fitting, parameter b is used to eliminate the periodic error of the function, parameter c is used to eliminate the eccentricity error existing in loading, and parameter d is used to eliminate the error. Based on this, the maximum hoop strain value |ε| _max corresponding to the thin-walled ring under each level of load is obtained.

The magnitude of the force and displacement is calculated according to the theoretical formula, and finally compared with the readings of the display instrument attached to the loading device. And draw the relationship curve between the theoretically calculated force and displacement and the actual measured value. As shown in Figures 4 and 5, it can be seen from the figures that the calculated results of the force and displacement measurement method based on distributed optical fiber sensing are very close to the actual measured values.

There is a relationship F=K ₁ ×|ε| _max and ΔD=K ₂ ×|ε| _max between the force and displacement at the vertex of the thin-walled ring and the maximum circumferential strain, and the calibration coefficient K is calculated according to the results obtained in the above steps ₁ and K ₂ sizes. The calibration coefficient can be used as a design parameter of the sensor.

It should be noted that, in addition to the above-mentioned embodiments, the utility model may also have other implementations. All technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the utility model patent.

Claims (3)

1. a kind of sensor device of the measurement based on distributed fibre optic sensing power and displacement, it is characterised in that main to include point Cloth straining and sensing optical fiber, thin wall circular, signal transmission fiber, optical fiber demodulating apparatus and computer；Distributed strain senses light Fibre is serially connected by signal transmission fiber with optical fiber demodulating apparatus, and computer and optical fiber demodulating apparatus are connected using serial ports, netting twine Connect；Described distributed strain sensing optical fiber is pasted on thin-wall circular ring-side wall.

2. according to claim 1 for the sensor device based on distributed fibre optic sensing power and the measurement of displacement, its It is characterised by, whole distributed strain sensing optical fiber is pasted along total length and be fixed on the side wall of thin wall circular.

3. according to claim 1 for the sensor device based on distributed fibre optic sensing power and the measurement of displacement, its It is characterised by, mutual welding, is cased with pyrocondensation outside fusion point between the distributed strain sensing optical fiber and signal transmission fiber Sleeve pipe.