CN1276237C - Rating method and instrument for distributing type optical fiber strain sensor - Google Patents

Abstract

Currently, distributed optical fiber strain sensors are extensively applied to various fields of construction, water engineering, traffic, petrifaction, electricity, medical treatment, machinery, power, ships, aviation, spaceflight, etc. The present invention discloses a special instrument for calibrating fundamental performance parameter indexes of the distributed optical fiber strain sensor. The instrument is composed of an equal-strength suspending beam, a temperature compensating plate, a static loading system, a dynamic loading system, a dynamic and static strain reference measuring system, a three-point deflection measuring system and data analyzing software, etc. The calibrating instrument can respectively apply static loads or dynamic loads to a distributed optical fiber strain sensor to be calibrated to calibrate a linearly dependent coefficient, a strain coefficient, a measuring error range, measuring accuracy and a measurement reproducibility index during static strain measurement. Additionally, the sampling frequency and the real time during dynamic strain measurement and the measurement error during static deflection measurement can be calibrated. The calibrated parameter indexes can be used for analysis, processing and evaluation of testing data of the distributed optical fiber sensor.

Description

Calibration method and instrument for distributed optical fiber strain sensor

1. Technical field

The invention belongs to the technical field of strain photoelectric signal monitoring and analysis, in particular to a calibrating method and instrument for a distributed optical fiber strain sensor.

2. Technical background

In the fields of civil engineering, water conservancy, transportation, petrochemical, electric power, medical treatment, machinery, power, ships, aviation, aerospace and other fields, strain is one of the important parameters to monitor and control the working status of engineering structures or equipment. For the measurement of the strain value, the traditional technology mostly uses electronic strain sensing devices (such as resistance strain gauges, vibrating wire strain sensors, differential resistance strain gauges, etc.), and all kinds of electronic strain sensors generally have poor durability, zero drift, Live work, susceptible to electromagnetic interference and other defects, in recent years with the development of optoelectronic technology, there has been a fiber optic sensing technology, which uses light as the carrier of signal collection and optical fiber as the medium for transmitting optical signals, with good durability, no Outstanding advantages such as zero drift, uncharged work, anti-electromagnetic interference, and large transmission bandwidth, especially the distributed optical fiber sensing technology, can realize continuous distributed or quasi-distributed measurement of the parameters to be measured. Therefore, in the above-mentioned various application fields, distributed optical fiber strain sensing systems are gradually replacing electronic strain sensing systems.

Before using distributed optical fiber strain sensors for strain measurement, the basic parameters of optical fiber strain sensors (linear correlation coefficient, gauge factor, sensor accuracy, repeatability, dynamic strain acquisition frequency, etc.) must be calibrated (calibrated). The existing calibration methods and items of calibration instruments are incomplete, especially the distributed optical fiber strain sensor based on Brillouin optical time domain reflectometer has not been applied on a large scale in engineering, and there is no calibration method for it.

3. Contents of the invention

Calibration method of distributed optical fiber strain sensor, equipped with equal-strength cantilever beam and temperature compensation block, there is a knife edge within 10mm from the top of the beam cantilever, which is used to suspend static loading, and there is a rectangular beam with a length of 80-150mm inside the knife edge Body, used to transmit static load; followed by the effective length of the cantilever beam of equal strength, generally greater than 1,000mm. The shape of the beam body along the axial direction is T-shaped, that is, one end is large and the other end is small. The upper surface of the beam body is marked with a scale on the central axis, which is used to determine the position of the distributed optical fiber sensor, that is, to install single-mode tight-buffered optical fiber or packaged single-mode Tight-buffered optical fibers or fiber gratings in point-type packaging, the single-mode tight-buffered optical fiber to be scaled is fixed on the upper and lower surfaces of the equal-strength beam with adhesive materials, and one end of the fiber is fixed at the temperature with the same adhesive material. The surface of the compensation block, and the other end is connected to the corresponding demodulation equipment for demodulating the distributed optical fiber strain sensor: first use the demodulation equipment to collect the initial strain value of the distributed optical fiber strain sensor; at the same time, use the dynamic and static strain gauge to collect the resistance strain gauge If the static load rate is fixed, it is also necessary to adjust or record the initial value of the dial gauge or dial gauge on the three-point deflection gauge; then load step by step, collect or record the distributed optical fiber strain sensor, resistance strain The readings of the deflection gauge and the three-point deflection gauge are used to determine the static load with a dial gauge or a dial gauge on the deflection gauge; at the same time, the dynamic loading system is used to vibrate the beam body, and the dynamic strain spectrum of the resistance strain gauge is collected with a dynamic and static strain gauge. Use the dynamic and static strain gauge to collect the dynamic load of the resistance strain gauge, compare and analyze the dynamic strain spectrum of the resistance strain gauge collected by the above dynamic and static strain gauge and the dynamic strain spectrum collected by the distributed optical fiber strain sensor demodulator to obtain the distribution to be scaled Sampling frequency of type optical fiber strain sensor and evaluate its real-time performance. The strain value measured by the demodulation system of the above distributed optical fiber strain sensor needs to deduct the strain value of the temperature compensation plate part to obtain the actual strain value of the beam body.

Under the static load, the distributed optical fiber strain sensor is used to collect the strain value of the equal-intensity beam repeatedly, and the measurement error, measurement accuracy and repeatability index of the distributed optical fiber strain sensor to be calibrated are obtained.

The composition of the instrument is as follows: According to the function, the instrument of the present invention consists of 7 parts, including: ① Equal strength cantilever beam ② Temperature compensation plate ③ Static loading system ④ Dynamic loading system ⑤ Dynamic and static strain reference measurement system ⑥ Three-point deflection measurement system ⑦ Data analysis software.

Equal-strength cantilever beams are composed of a beam body, two supporting column feet, a supporting pressure block, a pair of bases, three base leveling bolts and three air bubble levels.

The effective beam body length of the cantilever measuring beam with equal strength depends on the maximum value of the minimum spatial resolution that can be satisfied by various distributed optical fiber strain sensors applicable to the calibrator. There is a knife edge about 10mm inside the top of the beam, which is used to hang the static loading system. Inside the knife edge, there is a rectangular beam body with a length of about 133mm, which is used to transmit the static load; the effective length of the equal-strength cantilever beam is thereafter, generally greater than 1,000mm . The shape of the beam body along the axial direction is T-shape. This shape can ensure that after the cantilever beam is deformed under loading, the top surface of the beam body is under tension and the bottom surface is under compression. The compressive strain value produced by the point is also equal everywhere. The length of the fixed part at the root of the beam body is about 80mm, which ensures that the cantilever beam body can bear static and dynamic loads. The beam body material is manganese vanadium alloy steel. The central axis on the upper surface of the beam body is marked with a scale, which is used to determine the position of the distributed optical fiber sensor. The height of the two supporting columns is determined by the maximum deflection deformation of the cantilever beam under load. The cantilever beam body and the two column feet are fixed to each other by a supporting pressure plate. The base of this cantilever beam with equal strength is trapezoidal, and three base leveling bolts are respectively fixed under the three vertices. The base and the beam surface can be leveled according to whether the air bubbles in the bubble level at the midpoint of the three sides of the base are centered.

The temperature compensation plate is a square steel plate with a length of 1,000mm. The temperature compensation plate is used to measure the distributed optical fiber strain value caused by the ambient temperature change, and deduct it from the measured total distributed optical fiber strain value to remove Effects of temperature changes.

The static loading system consists of a hook and a series of weights. The hook is hung on the knife edge at the top of the cantilever beam, and the bottom of the hook is a support disc, on which weights can be hung step by step to apply static load.

The dynamic loading system is a mass block and a DC power supply. The mass block is suspended on a cantilever beam of equal strength. After the DC power supply is connected, the mass block will vibrate at a certain frequency and drive the beam body to vibrate at the same frequency to adjust the DC power supply. The voltage can adjust the amplitude of the beam body, and then adjust the size of the dynamic strain value of the beam body.

The dynamic and static strain reference measurement system includes several sheet resistance strain gauges and a dynamic and static strain test and analysis system. The resistance strain gauges are evenly arranged on the upper and lower surfaces of the beam along the axis of the beam body, and several resistance strain gauges for compensation are arranged on the temperature compensation plate. The specific arrangement depends on the bridge form adopted by the dynamic and static strain test and analysis system. The dynamic and static strain reference measurement system is connected to the PC through the RS-232 interface, and the strain signal is directly collected by the data acquisition software. strain value.

The three-point deflection measurement system is used to measure the deflection of the beam body under static load, including a fixed tool holder and a dial gauge or dial indicator. The fixed tool holder has two knife edges and is placed on the beam body. On the surface, the rod of the dial indicator goes deep into the fixed hole in the middle of the tool holder. When the beam body is deflected and deformed, the dial indicator will measure the deflection displacement of any point on the upper surface of the equal-strength beam body, and because each point on the upper surface The strain is the same, so the deflection displacement at any point on the upper surface of the beam is the same. According to the corresponding function of the vertical deflection at the end of the beam and the bending deflection of the beam, the vertical deflection at the end of the beam can be converted, and this can be used as a reference value for calculating the vertical deflection at the end of the beam through the distributed strain transformation measured by the distributed optical fiber sensor. The above is also the main basis for the compilation of data analysis software.

The advantages of the present invention are: the method and instrument of the present invention are a method and instrument specially used for calibrating the basic parameters of distributed optical fiber strain sensors, and are generally applicable to single-mode optical fibers for communication or packaged single-mode optical fibers and point-type packaging. Calibration of the basic parameters of various distributed optical fiber strain sensors such as optical fiber gratings. The calibration instrument can realize industrial standardized production and help to promote the application of distributed optical fiber strain sensing technology. It has outstanding advantages such as good durability, no zero drift, uncharged work, anti-electromagnetic interference, wide transmission bandwidth, and wide test temperature range.

4. Description of drawings

Figure 1 is a structural diagram of the distributed optical fiber strain sensor calibrator.

Figure 2 is the plane view of the equal strength beam

Figure 3 is a schematic diagram of the arrangement of distributed optical fiber strain sensors on the calibration instrument, taking single-mode tight-buffered optical fiber sensors and Brillouin optical time domain reflectometers as examples.

Fig. 4 is that the calibration instrument of the present invention records the linear fitting curve and correlation coefficient

5. Specific implementation plan

The following uses a single-mode tight-buffered optical fiber for communication as an example of a distributed optical fiber strain sensor to illustrate the specific use of this calibrator, but the use of this instrument is not limited to this.

(1) Layout of distributed optical fiber strain sensors

The distributed optical fiber strain sensor based on Brillouin optical time domain reflectometer can directly use the single-mode tight-buffered optical fiber in communication, or use the packaged single-mode tight-buffered optical fiber. Fix the single-mode tight-buffered optical fiber to be rated on the upper and lower surfaces of the equal-strength beam with the specified adhesive material, and fix one end of the optical fiber on the surface of the temperature compensation block with the same adhesive material, and the other end is connected to the Brillouin Optical Time Domain Reflectometer for Demodulating Distributed Fiber Optic Strain Sensors. As shown in Figure 3.

(2) Acquisition of initial values

Before applying a constant load, first use the optical time domain reflectometer to collect the initial strain value of the distributed optical fiber strain sensor; at the same time, use the dynamic and static strain gauge to collect the initial strain value of the resistance strain gauge. Or record the initial value of the dial indicator on the three-point deflection gauge.

(three), static load rating

1) Correlation coefficient, gauge coefficient and deflection measurement error

Hang the weights on the equal-strength beam hook one by one, and collect or record the readings of the distributed optical fiber strain sensor, resistance strain gauge and three-point deflection meter one by one. According to the collected readings under all levels of load, the correlation coefficient between the distributed optical fiber strain sensor and the strain value of the equal-strength beam measured by the resistance strain gauge and the gauge coefficient of the distributed strain sensor to be calibrated can be obtained by analysis. The analysis software is used to convert the distributed strain into the deflection of the equal-strength beam, and at the same time, the bending displacement measured by the three-point deflection meter is converted into the deflection of the equal-strength beam, so that the error range of the deflection measurement can be obtained.

2) Measurement error, measurement accuracy and repeatability indicators

Under a certain level of static load, the distributed optical fiber strain sensor is used to collect the strain value of the equal-strength beam repeatedly. Through mathematical statistical analysis, the measurement error, measurement accuracy and repeatability of the distributed optical fiber strain sensor to be calibrated can be obtained. index.

(four), the dynamic load ratio

1) Sampling frequency

The beam is vibrated by the dynamic loading system, the dynamic strain spectrum of the resistance strain gauge is collected by the dynamic and static strain gauge, and the dynamic strain spectrum of the distributed optical fiber strain sensor is collected at the same sampling frequency, and the dynamic strain spectrum of the two can be compared and analyzed. Obtain the sampling frequency of the distributed optical fiber strain sensor to be calibrated and evaluate its real-time performance.

(5), measurement range and measured data

The rate range of the distributed optical fiber strain sensor rate gauge is ±1000με. Figure 4 is a linear fitting curve of the rate value obtained by applying static load step by step, and the correlation coefficient of the curve is 0.999.

Claims (3)

1. Distributed optical fiber strain sensor calibration method, which is characterized in that it is equipped with an equal-strength cantilever beam and a temperature compensation block. There is a knife edge within 10mm of the cantilever top of the beam, which is used to suspend static loading. The length of the knife edge is 80 -150mm rectangular beam body, used to transmit static load; followed by the effective length of the cantilever beam of equal strength, the shape of the beam body along the axial direction is T-shaped, that is, one end is large and the other end is small, and the central axis of the upper surface of the beam body is marked with a scale , for the location of distributed optical fiber sensors, that is, to install single-mode tight-buffered optical fibers or packaged single-mode tight-buffered optical fibers or fiber gratings with spot packaging, and distribute and fix the single-mode tight-buffered optical fibers to be scaled with adhesive materials On the upper and lower surfaces of the equal-strength beam, one end of the optical fiber is fixed on the surface of the temperature compensation block with the same adhesive material, and the other end is connected to the demodulation system for demodulating the distributed optical fiber strain sensor: first use the distributed optical fiber The strain gauge demodulator collects the initial strain value of the distributed optical fiber strain sensor; at the same time, the dynamic and static strain gauge is used to collect the initial strain value of the resistance strain gauge. If the static load rate is fixed, it is also necessary to adjust or record the percentage on the three-point deflection gauge The initial value of the gauge or dial gauge; then load step by step, collect or record the readings of distributed optical fiber strain sensors, resistance strain gauges and three-point deflection gauges one by one, and use the deflection gauge to rate the static load of the dial gauge or dial gauge If the dynamic load rate is fixed, the beam body is vibrated by the dynamic loading system, the dynamic strain spectrum of the resistance strain gauge is collected by the dynamic and static strain gauge, and the distributed fiber optic strain sensor is collected by the distributed fiber optic strain sensor demodulator. The dynamic strain spectrum of the distributed optical fiber strain sensor is obtained by comparing and analyzing the dynamic strain spectrum of the resistance strain gauge collected by the dynamic and static strain gauge and the dynamic strain spectrum collected by the distributed optical fiber strain sensor demodulator, and the sampling frequency of the distributed optical fiber strain sensor to be calibrated is obtained and compared. Its real-time performance is evaluated, and the strain value of the temperature compensation section is deducted from the measured total distributed optical fiber strain value to remove the influence of temperature changes. 2. The calibrating method of the distributed optical fiber strain sensor according to claim 1 is characterized in that under static load, the strain value of the equal intensity beam collected by the distributed optical fiber strain sensor is repeated several times to obtain the distribution to be calibrated. The measurement error, measurement accuracy and repeatability index of the type optical fiber strain sensor. 3. Distributed optical fiber strain sensor calibration instrument, which is characterized by: a set equal strength cantilever beam, temperature compensation plate, static loading system, dynamic loading system, dynamic and static strain gauge or reference measurement system, three-point deflection measurement System Components: Equal-strength cantilever beams are composed of a beam body, two supporting column feet, a supporting block, a pair of bases, three base leveling bolts and three bubble levels; the three-point deflection measurement system includes a pair of fixed knives Holder and a dial indicator or dial indicator, the fixed tool holder has two knife edges, placed on the upper surface of the beam body, the rod of the dial indicator goes deep into the fixed hole in the middle of the tool holder, when the beam body is deflected and deformed, The dial indicator will measure the deflection displacement at any point on the upper surface of the equal-strength beam body, and since the strains at all points on the upper surface are the same, the deflection displacement at any point on the upper surface of the beam body is the same; The temperature compensation plate is a square steel plate with a length of 1,000mm. The temperature compensation plate is used to measure the distributed optical fiber strain value caused by the change of ambient temperature; the static loading system is a hook and a series of weights; the hook is hung on the cantilever beam On the knife edge at the top, the bottom of the hook is a support disc, on which weights can be hung step by step to apply static load; the dynamic loading system is a mass block and a DC power supply, and the mass block is suspended on an equal-strength cantilever beam , after the DC power supply is connected, the mass block will vibrate at a certain frequency, and drive the beam body to vibrate at the same frequency. By adjusting the voltage of the DC power supply, the amplitude of the beam body can be adjusted, and then the dynamic strain value of the beam body can be adjusted; The dynamic and static strain reference measurement system includes several sheet resistance strain gauges and a dynamic and static strain test and analysis system; The specific layout depends on the bridge form adopted by the dynamic and static strain test and analysis system. The above-mentioned strain gauges are connected to the PC through the RS-232 interface, and the strain signals are directly collected by the data acquisition software. It is connected with the distributed optical fiber strain gauges. The measurement system used by the sensors works synchronously to obtain two sets of strain values measured by the two sensors respectively.

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