CN203658011U - Optical fiber balance for wind tunnel test measurement - Google Patents

Abstract

The utility model discloses an optical fiber balance used for wind tunnel test measurement, which comprises a balance main body, a fixed end, upper and lower notches, a loading head, and an optical fiber grating strain gauge. On the measuring platform; the main body of the balance is provided with an upper notch and a lower notch near the fixed end. The upper and lower notches are arranged symmetrically and have the same size. The other end of the main body of the balance is provided with a loading head, and a suspension assembly is installed on the loading head for Loading and unloading weights. Fiber Bragg grating strain gauges are respectively pasted on the upper and lower notches along the axis of the main body of the balance. After the fiber grating strain gauges are fixed, one end is placed freely, and the other end is connected to the fiber optic demodulator. The displacement is measured, and the optical fiber demodulator converts the received optical signal into a wavelength value and displays it on the computer panel. The use of fiber optic balance greatly improves the measurement accuracy of the wind tunnel test under the action of small-scale aerodynamic force.

Description

A Fiber Optic Balance for Wind Tunnel Test Measurement

technical field

The utility model relates to a wind tunnel balance, in particular to an optical fiber balance used for wind tunnel test measurement.

Background technique

Wind tunnel balances are sensors that measure forces and moments in wind tunnel experiments. Point out in the existing open document " wind tunnel balance ": current strain balance is all to be sensitive element with resistance strain gauge. When in use, the resistance strain gauge with similar resistance value and temperature coefficient effect is composed of a Wheatstone bridge and pasted on the surface of the test piece for measurement, in which the resistance strain gauge converts the strain of the test piece into the resistance change. , the Wheatstone bridge converts the resistance change into a voltage signal output. The relationship between the output signal and the calibration load is obtained through static calibration experiments, that is, by loading and unloading weights, the tested piece is deformed under the action of the load, and its strain is proportional to the load. The strain gauge pasted on the surface of the test piece is also deformed at the same time, so that its resistance value changes, and it is converted into a voltage change by the Wheatstone bridge, so as to obtain the relationship between load and voltage, so that in the application according to the output The electrical signal is used to obtain the aerodynamic load acting on the model under test. As a device for directly measuring the aerodynamic load in wind tunnel experiments, the wind tunnel balance is of great significance to understand the performance of the aerospace vehicle during the development process, and it is necessary to improve the sensitivity of the sensor during the measurement process.

According to the wind tunnel balance specification, the sensitivity is measured by the magnitude of the sensitive load. Sensitive load refers to the load value that needs to be applied when the measuring element of the balance changes the unit degree. Here, the sensitivity is measured by the microstrain produced per unit force. In the force measurement experiment, the existing wind tunnel balance structure is to paste the strain gauge on the beam bearing the strain. However, due to the high stiffness of the balance material, the resulting strain value is small, and the output signal is small or even submerged in the interference signal in the small-range aerodynamic measurement. middle. Therefore, the traditional wind tunnel balance has the problems of low resolution and weak sensitivity in small-scale aerodynamic measurement experiments.

Utility model content

In order to avoid the deficiencies of the prior art, the utility model proposes a fiber optic balance for wind tunnel test measurement. The fiber optic balance adopts a slot at the balance main body near the fixed end, and a fiber grating strain gauge is pasted on the notch. The displacement of the notch after being loaded is measured; the optical fiber balance is used to greatly improve the measurement accuracy of the wind tunnel test under the action of small-scale aerodynamic force.

The technical scheme adopted by the utility model to solve its technical problems is: comprising a fiber grating strain gauge, a fixed end, an upper notch, a lower notch, a balance main body, a loading head, the balance main body and the fixed end are integrally structured, and the fixed end has a Four evenly distributed through holes are installed on the measuring platform by bolts; there are upper and lower notches on the main body of the balance near the fixed end, and the upper and lower notches are symmetrically arranged with the same size, and the other end of the balance main body has a loading head , the suspension assembly is installed on the loading head for loading and unloading weights; the fiber grating strain gauge is respectively pasted on the upper notch and the lower notch along the axis of the balance main body. After the fiber grating strain gauge is fixed, one end is placed freely, and the other end The fiber optic demodulator is connected, and the fiber optic demodulator converts the received optical signal into a wavelength value and displays it on the computer panel.

The distance between the upper notch, the lower notch and the fixed end is 10mm.

Beneficial effect

The fiber optic balance proposed by the utility model for wind tunnel test measurement, in the balance static calibration experiment, the fiber optic balance is obtained as the relationship between the wavelength and the load value, and the resistance balance is obtained as the relationship between the electrical signal and the load value, both of which can be converted into The relationship between force and strain, and then compare its sensitivity: for resistance strain gauges, the strain value can be calculated from the measured voltage value, supply bridge voltage, and strain gauge sensitivity coefficient; for fiber grating strain gauges, the wavelength change of 1pm corresponds to With 1.2με, the corresponding strain value can be obtained by measuring the change value of the wavelength. In the experiment, compared with the resistance strain gauge, the output sensitivity of the fiber Bragg grating strain gauge is doubled, the resistance strain gauge is 15με/N, and the fiber optic strain gauge is 32με/N, which increases the strain value generated under the same load .

When the load of the utility model is the same in the small range range, the output of the fiber grating strain gauge is twice that of the resistance strain gauge, and the output signal is large, which is easy to meet the minimum resolution of the instrument, and is not easy to be submerged in the noise; the use of the fiber optic balance greatly improves the The measurement accuracy of wind tunnel test under small range aerodynamic force.

Description of drawings

A fiber optic balance used for wind tunnel test measurement of the present utility model will be further described in detail in conjunction with the accompanying drawings and embodiments below.

Fig. 1 is a schematic diagram of the optical fiber balance of the present invention.

Fig. 2 is a schematic diagram of installation of the optical fiber balance of the present invention.

In the picture:

1. Fiber Bragg grating strain gauge 2. Fixed end 3. Upper notch 4. Lower notch 5. Balance main body 6. Loading head 7. Suspension component 8. Optical fiber demodulator 9. Computer 10. Measuring platform

Detailed ways

This embodiment is a fiber optic balance used for wind tunnel test measurement.

Referring to Fig. 1 and Fig. 2, the fiber optic balance of the present invention is composed of a fiber grating strain gauge 1, a fixed end 2, an upper notch 3, a lower notch 4, a balance main body 5, and a loading head 6. The main body 5 of the balance and the fixed end 2 are integrally constructed. The size of the fixed end is 120 mm in length, 90 mm in width and 22 mm in height. There are four evenly distributed through holes on the fixed end, and it is fixed on the measuring platform 10 by bolts. The upper notch 3 and the lower notch 4 are arranged on the balance main body 5 near the fixed end 10mm, and the upper and lower notches are arranged symmetrically and have the same size; the balance main body is 200mm long, 14mm wide, and 20mm high; The dimensions of the slots are 10mm in length, 14mm in width, and 1mm in depth, and the length of the slots is not less than the length of the grid area of the fiber grating; the width is the same as that of the main body of the balance. Combined with the measurement range of the fiber grating and the finite element analysis, that is, when the strain value generated by the load on the pre-stretched foundation does not exceed the maximum irreversible deformation of the grating area, the groove depth is selected as 1mm. The pre-stretching means that when the two ends of the grating area of the fiber grating strain gauge 1 are axially pasted on the notch of the main body of the balance, in order to measure the compressive strain generated by the positive and negative normal forces, the upper and lower optical fibers are stretched before pasting. The pre-stretching size is 2nm. When operating, first fix one end of the grating area on one end of the notch, and fix the fiber pigtail at the other end on a fixing device with a spiral micro-movement, and connect it to the fiber optic demodulator through a fiber jumper , the rotating helical micrometer moves to the optical fiber demodulator 8 to show that the wavelength change is about 2.5nm, and the other end of the fixed grating area is at the other end of the notch. Use AB glue to stick the optical fiber to the notch. During the curing process of the AB glue, the stretching amount will be reduced, so the stretching amount of 2nm needs to be stretched by about 2.5nm. The fiber Bragg grating strain gauge 1 achieves the purpose of sensing through the change of the central wavelength. The fiber grating strain gauge 1 includes 1m long pigtails at both ends, which play the role of optical signal transmission; the middle 10mm grating area plays the role of sensing. The basic principle is: when the wide-spectrum light passes through the grating, it satisfies the Bragg formula condition All wavelengths of light can be partially or fully reflected. The Bragg formula shows that the central wavelength of the fiber is related to the effective refractive index and the period of the grating, and then the reaction is affected by the strain.

The working process of the utility model:

The fixed end 2 of the fiber optic balance is fixed on the measurement platform 10 by four bolts, and the other end, namely the free end, is used for static calibration experiment loading. The suspension assembly 7 is connected with the balance main body 5 through the loading head 6, and is used for loading or unloading weights in experiments. One end of the fiber grating strain gauge 1 is freely placed, and the other end is fused together with the fiber jumper through a fiber fusion splicer. The fiber grating demodulator 8 has a built-in laser light source. The light source emits broad-spectrum light, which is transmitted to the grating area by the optical fiber jumper and fiber pigtail. Transmission to the fiber grating demodulator 8, the fiber grating demodulator 8 reacts the received optical signal into a wavelength value and displays it on the computer 9 panel. When the weight is not loaded, the original wavelength of the fiber grating is measured; when the weight is loaded, the main body of the balance is deformed by force, the upper surface produces tensile strain, and the lower surface produces compressive strain. The applied load value is proportional to the strain, and the grating period changes due to the strain, so that the wavelength of the upper and lower surfaces satisfying the Bragg formula changes, the wavelength reflected by the fiber grating grating area changes, and the display value of the corresponding channel of the fiber grating demodulator 8 changes. In order to easily distinguish the wavelengths of the upper and lower fiber gratings during measurement, there is a wavelength difference of 5nm when the fiber grating is selected. The utility model selects a fiber grating with a center wavelength of 1550nm on the upper surface and a center wavelength of 1555nm on the lower surface, which is displayed on the computer. It is convenient for observation and recording. In the static calibration experiment, by loading and unloading weights, record the wavelength variation measured by the fiber grating demodulator 8, and obtain the relationship between load and wavelength, so as to obtain the load on the model according to the output wavelength signal in the application.

Claims (2)

1. a kind of fiber optic balance that is used for wind tunnel test measurement, it is characterized in that: comprise fiber grating strain gauge, fixed end, upper notch, lower notch, balance main body, loading head, balance main body and fixed end are integrated structure, There are four evenly distributed through holes on the fixed end, which are installed on the measuring platform by bolts; the upper and lower notches are arranged on the main body of the balance near the fixed end, and the upper and lower notches are symmetrically arranged with the same size. There is a loading head at one end, and the suspension assembly is installed on the loading head to load and unload weights; the fiber grating strain gauge is respectively pasted on the upper notch and the lower notch along the axis of the main body of the balance. After the fiber grating strain gauge is fixed, one end is free to place , and the other end is connected to the fiber optic demodulator, which converts the received optical signal into a wavelength value and displays it on the computer panel. 2. the fiber optic balance that is used for wind tunnel test measurement according to claim 1, is characterized in that: the distance of upper notch, lower notch and fixed end is 10mm.

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