Linear expansion coefficient measuring system

Abstract

The invention relates to a linear expansion coefficient measuring system, which belongs to the technical field of linear expansion coefficient measurement, and comprises a laser, a plane mirror bracket vertically arranged on a path of a horizontal light beam emitted by the laser, a barrier strip arranged on one side of the top of the plane mirror bracket close to the laser, and a plane mirror horizontally arranged on the top of the plane mirror bracket, according to the invention, the light beam emitted by the laser and the light beam reflected by the plane mirror form interference fringes, and meanwhile, the heating rod is used for heating the to-be-measured material to enable the to-be-measured material to expand, so that the to-be-measured material can be accurately measured. The side, away from the barrier strip, of the plane mirror is pushed to move upwards, the barrier strip limits displacement of the plane mirror in the horizontal direction, the angle of the plane mirror is adjusted to change the interval of interference fringes, the linear expansion coefficient of the to-be-measured material is calculated according to the change of the interval, and the measurement precision of the linear expansion coefficient is improved.

Description

Technical Field

[0001] This invention belongs to the field of linear expansion coefficient measurement technology, and specifically relates to a linear expansion coefficient measurement system. Background Technology

[0002] In materials science, physics, and engineering, the linear coefficient of thermal expansion (CTE) is a crucial physical quantity that directly affects the dimensional stability of materials under temperature variations. In industries such as manufacturing and construction, thermal expansion is a critical factor that engineers and architects must understand to ensure that material structures are not damaged by temperature changes. Accurate measurement and understanding of a material's thermal expansion properties are essential for design optimization, improved manufacturing precision, and structural stability. However, traditional expansion measurement techniques suffer from insufficient accuracy, limited operating space, and complex procedures. For example, when measuring the CTE of transparent objects, the DIC system produces speckle patterns within the transparent object, preventing the camera from capturing the correct pattern and resulting in an incorrect CTE. Furthermore, the speckle pattern may not adhere firmly to the surface of the transparent object, limiting its effectiveness in high-precision measurements and broad applications. Therefore, developing novel, high-precision, and highly stable expansion measurement instruments has become an urgent problem to solve.

[0003] Currently, utilizing the properties of light to amplify minute phenomena for precise measurement is a common method in modern technology. The Loehr mirror interferometer is a novel measuring device based on the principle of optical interference. With its unique advantages of high measurement accuracy, wide operating range, and simple operation, it has become a research hotspot in the field of dilatation measurement technology.

[0004] Existing interferometric dilatometers have limitations in terms of measurement range and environmental adaptability. While the Michelson interferometer is widely used for measuring minute displacements, it faces several limitations when measuring thermal expansion, such as the large number of optical components and complex adjustments. The Michelson interferometer also requires counting the movement of interference fringes, demanding a high level of operator skill. Traditional differential measurement methods are technically complex, suffer from uneven temperature gradients, and are costly; for example, temperature differences at both ends of the heating furnace can lead to uneven heating of the measured material. Furthermore, the application potential of interferometric dilatometers in other fields has not yet been fully explored. Summary of the Invention

[0006] In view of this, the present invention provides a linear expansion coefficient measurement system to overcome the shortcomings of the prior art. The present invention can limit the horizontal displacement of the plane mirror, thereby improving the accuracy of linear expansion coefficient measurement.

[0007] The technical solution of the present invention is: a linear expansion coefficient measurement system, including a laser, a plane mirror support vertically arranged in the path of the horizontal beam emitted by the laser, a baffle is provided on the top of the plane mirror support near the laser, the baffle is perpendicular to the beam, a plane mirror is horizontally arranged on the top of the plane mirror support, one end of the plane mirror abuts against the baffle, and the other end extends out of the plane mirror support, the material to be measured is placed on the side of the plane mirror support away from the laser, and the material to be measured abuts against the lower side of the plane mirror, the beam emitted by the laser and the beam reflected by the plane mirror form interference fringes, a heating rod is arranged inside the material to be measured, the material to be measured expands due to heat and pushes the side of the plane mirror away from the laser to move upward, so as to adjust the angle of the plane mirror, thereby changing the spacing of the interference fringes.

[0008] Preferably, a support plate is horizontally provided on the top of the plane mirror bracket, the support plate is connected to the plane mirror bracket, and a baffle is fixed on the edge of the support plate near the laser.

[0009] Preferably, a connecting arm is obliquely provided between the plane mirror bracket and the support plate. One end of the connecting arm is fixedly connected to the plane mirror bracket, and the other end extends away from the laser and is fixedly connected to the support plate.

[0010] Preferably, the baffle has a notch in the middle, through which the laser beam passes.

[0011] Preferably, it also includes a temperature sensor, which is fixed on the material to be measured.

[0012] Preferably, the material to be measured is a tube, and a copper tube support is horizontally arranged on the side of the plane mirror support away from the laser. The copper tube support is connected to the plane mirror support, and the tube is vertically arranged between the copper tube support and the plane mirror and abuts against them respectively. The heating rod is arranged in the tube and fixedly connected to it.

[0013] Preferably, it also includes a beam expander, which is vertically positioned between the laser and the plane mirror support, and the beam expander is coaxial with the center line of the laser emitter.

[0014] Preferably, the focal length of the beam expander is 45mm.

[0015] Preferably, it also includes: a light screen, which is vertically positioned on the side of the plane mirror bracket away from the laser.

[0016] Preferably, it also includes a CCD camera to acquire interference fringe images.

[0017] Compared with existing technologies, the linear expansion coefficient measurement system provided by this invention uses a laser, a plane mirror support, and a plane mirror in combination to form interference fringes between the laser beam emitted by the laser and the beam reflected by the plane mirror. At the same time, a heating rod is used to heat the material to be measured, causing it to expand. This expands the plane mirror, pushing the side away from the stop bar upward. The stop bar restricts the horizontal displacement of the plane mirror. By adjusting the angle of the plane mirror, the spacing of the interference fringes is changed. The linear expansion coefficient of the material to be measured is calculated based on the change in the spacing, thereby improving the accuracy of the linear expansion coefficient measurement. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the measurement system of the present invention; Figure 2 This is the present invention. Figure 1 Enlarged diagram of point A in the diagram; Figure 3 This is a cross-sectional view of the tube body of the present invention; Figure 4 This is a schematic diagram of the interference principle of the Loe mirror of the present invention; Figure 5 This is a wiring diagram of the single-head heating rod of the present invention; Figure 6 This is a connection diagram of the temperature control system of the present invention; Figure 7 This is an interference fringe pattern captured by the present invention; Figure 8 This is the interference fringe intensity distribution diagram obtained by the present invention; Figure 9 This is a comparison image of the Loe lens interference expansion before and after the invention. Detailed Implementation

[0020] This invention provides a system for measuring the coefficient of linear expansion, which is described below in conjunction with... Figures 1 to 9 The present invention is illustrated by the structural diagram shown below.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the technical solution of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Reference Figure 1 , Figure 1 This is a schematic diagram of the measurement system in this embodiment. A linear expansion coefficient measurement system includes a laser 1, a plane mirror support 2 vertically positioned in the path of the horizontal beam emitted by the laser 1, a baffle 21 on the top of the plane mirror support 2 near the laser 1, the baffle 21 being perpendicular to the beam, a plane mirror 3 horizontally positioned on the top of the plane mirror support 2, one end of the plane mirror 3 abutting against the baffle 21, and the other end extending out of the plane mirror support 2, the material to be measured 10 being placed on the side of the plane mirror support 2 away from the laser 1, the material to be measured 10 abutting against the lower side of the plane mirror 3, the beam emitted by the laser 1 passing through the plane mirror 3 and forming interference fringes with the beam reflected by the plane mirror 3, a heating rod 4 being placed on the material to be measured 10, the material to be measured 10 expanding due to heat pushing the side of the plane mirror 3 away from the baffle 21 upwards to adjust the angle of the plane mirror 3, thereby changing the spacing of the interference fringes.

[0023] The linear expansion coefficient measurement system in this embodiment controls the temperature of the material to be measured 10 to cause it to thermally expand, thereby causing the plane mirror to tilt at a certain angle, which ultimately leads to a change in the spacing of the interference fringes. The change in the spacing of the interference fringes reflects the elongation of the material due to thermal expansion.

[0024] The principle of the Loehr mirror interference experiment is as follows: Figure 4 As shown, It is a point light source. yes The virtual image formed by mirror M for and The spacing, yes Vertical distance from the screen. The emitted light is partially grazed (the angle of incidence is close to 0). The reflected light (equivalent to light from the Loewe mirror) is reflected from the mirror. The emitted beam of light and directly from The emitted light beams originate from the same wavefront, therefore they are coherent. In the overlapping region of the two beams ( Figure 4 Interference occurs in the gray shaded areas (in the image), forming interference fringes.

[0025] Within a certain temperature range, a solid rod increases in length as the temperature rises. At room temperature, the length of the solid rod is... With temperature The relationship is as follows:

[0026] in, This is called the coefficient of linear expansion, and its value depends on the properties of the material itself. Its unit is 1 / ; This is the original length of the solid rod at room temperature.

[0027] If the solid rod is at temperature The length of time is The temperature rises to At that time, the length of the solid rod increased Therefore, we can obtain: in, This represents the change in temperature.

[0028] According to equation (2), it can be seen that it is only necessary to accurately measure the original length of the solid rod. and the change in length of the solid rod with temperature The coefficient of linear expansion of the material can then be calculated. .

[0029] In the formula According to equation (2), it can be seen that only the original length of the copper tube needs to be accurately measured. The change in copper tube length with temperature The coefficient of linear expansion of the material can then be calculated. .

[0030] For example: the thermal expansion coefficient of copper tubes is known. = 1.85× m / ℃ means that a one-meter-long copper tube will linearly expand by 18.5 μm for every 1 degree Celsius increase in temperature. If the length of the copper tube... = 50 mm, during the process of heating from room temperature 25℃ to 65℃, ∆T = 40℃, at which point the theoretical linear expansion length of the brass pipe ∆L = = 37 μm. The accuracy of ∆L measurement directly affects the coefficient of linear expansion of the material. The specific measurement method for ∆L is as follows.

[0031] (1) The actual optical path is as follows Figure 9 As shown, the light path when the plane mirror is placed horizontally is drawn with solid lines, and the light path when the mirror tilts due to expansion is drawn with dashed lines.

[0032] Figure 9 In the middle: d is the distance between the real laser S and the virtual laser S' when the plane mirror is placed horizontally; The distance between the real laser S and the virtual laser S'' after the mirror is tilted; x is the horizontal distance from the laser to the front of the mirror; Let be the length of the light ray in the plane mirror; The actual height of the mirror tilt = the expansion length of the copper pipeline; D is the total length from the laser to the screen; The total length of the interference fringes on the screen; The actual fringe spacing of the image formed by the interference of the Loehn mirror when the plane mirror on the screen is placed horizontally. This represents the actual stripe spacing after the mirror surface expands and tilts.

[0033] (2) When the plane mirror is placed horizontally, the angle between the light emitted by the point laser S and the front section of the mirror is ∠γ. At this time, according to the interference principle, the distance between the real laser S and the virtual laser S' can be obtained ( (Laser wavelength) (3) In the experiment, the expansion of the copper tube caused the plane mirror in the Loewe mirror system to tilt at a certain angle, with the side of the mirror closest to the laser fixed. According to the Loewe mirror interference principle, the virtual laser S The position is changed to S At this location, we can obtain the result using the formula. By combining the two equations, it is easy to obtain In the experiment, the mirror surface is tilted by expanding the copper tube. Let the tilt angle be θ. Then, according to the similar triangle theorem, ∠S SS = ∠θ. At this point, the tilt height of the rear end of the mirror is the height ΔL of the copper tube due to the temperature increase, calculated based on the length of the plane mirror. It can be deduced

[0034] Based on the triangular relationship, we can obtain Further push Because of ∠ Minimal, with little effect on the equation, here we will use cos ≈ 1, expanding the equation gives Combining the above equations, we get The quantity we are looking for in the formula is , and All data were obtained through CCD camera and MATLAB calibration measurements. The formulas were then organized to obtain... Based on this formula, d and d can be omitted at this point. Two data points that are difficult to measure can be obtained by substitution, simply by measuring the spacing of the interference fringes. The conclusion is The specific value.

[0035] The linear expansion coefficient measurement system based on the Loe mirror interference principle can not only significantly improve measurement performance, but also has broad application potential in many aspects such as material performance analysis, structural design optimization and precision manufacturing. Its research and development has important practical value and broad market prospects.

[0036] Lasers are ideal light sources due to their monochromaticity, stability, coherence, and brightness. In this embodiment, laser 1 is a helium-neon laser. Helium-neon lasers use neutral atomic gases helium and neon as working substances and are a type of gas laser.

[0037] In the above embodiment, the laser 1 and the plane mirror support 2 of the linear expansion coefficient measurement system are mounted on the optical bench 12. The optical bench 12 is provided with a track along its length. The laser 1 and the plane mirror support 2 are mounted on the track and can move along the track. The optical bench 12 is equipped with a level 13.

[0038] As a further optimization, in this embodiment, the top of the plane mirror bracket 2 is provided with a support plate 22, which is connected to the plane mirror bracket 2, and the baffle 21 is fixed on the edge of the support plate 22 near the laser 1.

[0039] In this embodiment, the plane mirror 3 is supported by the support plate 22, which improves the stability of the plane mirror 3 and further improves the accuracy of the linear expansion coefficient measurement.

[0040] The support plate 22 is 25mm shorter than the plane mirror, so that the plane mirror 3 extends out of the support plate 22 and directly contacts the material to be measured 10. At the same time, in order to prevent the material to be measured 10 from overheating and damaging the plane mirror 3, heat insulation sponge is set on the lower side of the plane mirror 3 to avoid direct contact between the mirror surface and the heat source, reduce the influence of uncontrollable factors, and ensure the accuracy and safety of the measurement.

[0041] As a further optimization, in this embodiment, a connecting arm 23 is obliquely arranged between the plane mirror bracket 2 and the support plate 22. One end of the connecting arm 23 is fixedly connected to the plane mirror bracket 2, and the other end extends away from the laser 1 and is fixedly connected to the support plate 22.

[0042] Reference Figure 2 , Figure 2This is an enlarged schematic diagram of point A of the measurement system in this embodiment. As a further optimization, a notch 211 is provided in the middle of the baffle 21 in this embodiment, and the beam emitted by the laser 1 passes through the notch 211.

[0043] In this embodiment, the notch 211 on the baffle 21 allows the light beam to pass through the notch 211 and then through the plane mirror 3, ensuring the smoothness of the light path and also ensuring that the plane mirror 3 remains fixed in the horizontal direction.

[0044] As a further optimization, this embodiment also includes a temperature sensor 5, which is fixed on the material to be measured 10.

[0045] In this embodiment, the temperature of the material to be measured 10 is accurately measured by the temperature sensor 5, thereby accurately heating the material to be measured 10 by the heating rod 4.

[0046] In this embodiment, the temperature sensor 5 is a DS18B20. The DS18B20 is a single-bus digital temperature sensor, known for its small size, high accuracy and strong anti-interference capability, making it very suitable for digital temperature measurement and control in compact devices.

[0047] This system is also equipped with an OLED display, namely organic light-emitting diode. OLEDs have excellent characteristics such as self-illumination, no need for backlight, high contrast, thinness, wide viewing angle, fast response speed, applicability to flexible panels, wide operating temperature range, and simpler construction and manufacturing process.

[0048] In this embodiment, the DS18B20 temperature sensor is bound together with the material to be measured 10, and the DS18B20 temperature sensor is connected to an OLED display screen to display the temperature of the material to be measured in real time on the OLED display screen.

[0049] The linear expansion coefficient measurement system in this embodiment is also equipped with a relay. When the preset temperature is reached, the relay will disconnect the power supply and stop heating. When the temperature of the material to be tested is lower than the preset temperature, the relay will turn on the power supply and start heating.

[0050] Reference Figure 3 , Figure 3 This is a cross-sectional view of the tube body in this embodiment. As a further optimization, the material to be measured 10 in this embodiment is a tube body. A copper tube support 24 is horizontally arranged on the side of the plane mirror support 2 away from the laser 1. The copper tube support 24 is connected to the plane mirror support 2. The tube body is vertically arranged between the copper tube support 24 and the plane mirror 3 and abuts against them respectively. The heating rod 4 is arranged in the tube body and is fixedly connected to it.

[0051] In this embodiment, the material to be measured 10 is a tube (e.g., copper tube, iron tube, aluminum tube, etc.), which makes it convenient to put the heating rod 4 into the tube for uniform heating, reducing uncontrollable variables in the measurement process and improving accuracy.

[0052] In the above embodiment, the inner diameter of the tube should match that of the heating rod 4 to ensure that temperature changes can be effectively transmitted to the tube.

[0053] In the above embodiments, a linear expansion coefficient measurement system is used to measure the thermal expansion behavior of copper tubes in the temperature range of 25 to 65°C. Compared with traditional interferometric dilatometers, the method is simpler and the cost is relatively low.

[0054] In this embodiment, heating rod 4 is a stainless steel single-ended heating rod with a diameter of 5.96 mm and a length of 50 mm. The heating tube wire end is connected to the temperature controller, and the heating rod part is connected to the copper tube to be tested. Figure 6 As shown, Figure 6 This is a schematic diagram of the external wiring of a single-headed heating rod. The heating rod uses an external wiring structure, where the lead rod and lead wire are connected outside the heating element via crimp terminals. The external wiring structure uses a fiberglass sleeve to wrap the wiring joint, increasing insulation and better protecting the lead wire from excessive bending. Alternatively, in this embodiment, the heating rod can also use an internal wiring structure, such as... Figure 5 As shown, Figure 5 This is a schematic diagram of the internal wiring of a single-headed heating rod.

[0055] Copper has advantages such as good thermal conductivity and ductility. Considering the fit with the heating rod, a brass tube with an inner diameter of 6 mm, an outer diameter of 8 mm, and a length of 50 mm was selected as the main material for measuring the coefficient of thermal expansion in the experiment. The heating rod was embedded inside the copper tube. From the initial design stage, the issue of achieving uniform heating was considered; therefore, the length and size were designed to fit perfectly when the material was custom-purchased. To ensure a perfect fit, a gap of 0.04 mm was left during the custom-made heating rod process.

[0056] In this embodiment, since a single-ended heating rod is installed inside the copper tube, and a lead wire extends from one end of the heating rod, a long groove is designed on the copper tube support 24. This is done to allow the lead wire to extend smoothly and to ensure the stability of the copper tube when placed vertically.

[0057] As a further optimization, this embodiment also includes a beam expander 6, which is vertically disposed between the laser 1 and the plane mirror support 2, and is coaxial with the center line of the laser 1's emitting end.

[0058] In this embodiment, the laser beam is expanded by the beam expander 6 to obtain a clear and distinct interference image, improve the effect of interference fringe display, and further improve the accuracy of linear expansion coefficient measurement.

[0059] As a further optimization, the focal length of the beam expander 6 in this embodiment is 45mm.

[0060] In the above embodiments, to obtain a clearer and more distinct interference image, a beam expander was added to expand the laser beam. Four beam expanders with focal lengths f of 4.5mm, 6.2mm, 15mm, and 45mm were selected for testing. The tests revealed that lenses with shorter focal lengths caused excessive laser beam expansion, easily generating more noise and affecting experimental observation and data measurement. Ultimately, a beam expander with a focal length f of 45mm was chosen.

[0061] In this embodiment, the beam expander 6 is mounted on a track on the optical bench 12 and can move along the track. The height of the beam expander 6 can be adjusted using a telescopic bracket.

[0062] In addition, a polarizer 14 is vertically arranged on the optical bench 12. The polarizer 14 is located between the beam expander 6 and the laser 1. The intensity of the light beam emitted by the laser can be adjusted by using the polarizer 14.

[0063] As a further optimization, this embodiment also includes a light screen 7, which is vertically arranged on the side of the plane mirror bracket 2 away from the laser 1.

[0064] In this embodiment, the laser is adjusted so that when the screen 7 moves on the guide rail, the position of the laser spot on the screen 7 remains unchanged, ensuring that the laser is initially placed horizontally.

[0065] As a further optimization, this embodiment also includes a CCD camera 8 to acquire interference fringe images. The CCD camera 8 is vertically positioned on the side of the plane mirror bracket away from the laser. The CCD camera 8 is perpendicular to the light beam, and the resulting interference fringes fall on the CCD camera 8.

[0066] In this embodiment, a CCD camera 8 is used to display the formed interference fringes, which facilitates the acquisition of the interference fringes and the calculation of the linear expansion coefficient of the material.

[0067] In this embodiment, the method of extracting the light intensity of interference fringes using MATLAB is used to facilitate the measurement of the interference fringe spacing and the interference fringe spacing after specular expansion.

[0068] In this embodiment, interference images were acquired using a CCD camera 8. By extracting the intensity of the interference fringes and using MATLAB data processing technology, the change in the fringe spacing after the copper tube expanded was measured, and the length of the copper tube expansion was deduced, thereby obtaining the expansion coefficient of the copper tube.

[0069] The CCD camera 8 in this embodiment, also known as a charge-coupled device camera, is an electronic imaging device commonly used for image capture and video surveillance. It can convert the optical image received by the photosensitive element into an electrical signal, and then generate a digital image through digital signal processing technology.

[0070] like Figure 7 The image shown is an interference fringe image captured by a CCD camera. To measure the expansion of the copper tube as it heats from 25°C to 65°C, five sets of heating experiments were conducted. During the gradual temperature increase, the interference fringes showed a noticeable, minute shift to the naked eye. Finally, the camera captured five sets of interference fringe images during the heating process. The fringes in the images are relatively clear and easy to analyze statistically.

[0071] The linear expansion coefficient measurement system in this embodiment is also equipped with a power supply. The power supply is a YB1731A DC regulated power supply, which is a power supply device with dual outputs. It has voltage and current regulation functions and can automatically switch between voltage and current regulation states.

[0072] The linear expansion coefficient measurement system of the present invention effectively combines an optical system with a temperature control system 15. The system composition of the temperature control system 15 is as follows: Figure 6 As shown, the thermal expansion coefficient of a copper tube was measured using a linear expansion coefficient measurement system, and its performance at different temperatures was analyzed. The measurement results were compared and verified with existing methods. The thermal expansion coefficient was deduced by observing changes in optical path interference phenomena, and the uncertainty and error of the data were calculated.

[0073] The entire linear expansion coefficient measurement system uses a helium-neon laser as the light source, whose emitted 0.6328-micron red light exhibits good monochromaticity and coherence. To obtain clear interference images, a beam expander with a focal length of 45mm was selected to extend the laser beam. For temperature control, a DS18B20 temperature sensor, an OLED display, a stainless steel single-head heating rod, and a relay were used to display and control the temperature of the copper tube in real time. To maintain the stability and safety of the optical path of the measurement system, a plane mirror and the copper tube were fixed by a support plate and a copper tube bracket, respectively. Interference image capture relies on a CCD camera 8, which converts optical images into digital signals. Power is supplied by a YB1731A DC regulated power supply, ensuring power stability and safety. Finally, through careful design and adjustment, a stable interference system was established, reducing the influence of uncontrollable factors on the optical path, thereby ensuring the accuracy and reliability of the experimental results.

[0074] This embodiment provides a measurement method for a linear expansion coefficient measurement system. (10) Wipe each optical component in turn with a disposable alcohol wipe; (11) Turn on the helium-neon laser, wait for the light intensity to stabilize, and then adjust the optical path to be horizontal; (12) Adjust the center of the beam expander so that the light passes through the center of the beam expander; (13) Place the plane mirror and use a level to ensure that the plane mirror is horizontal; (14) Adjust the polarizer to make obvious interference fringes appear on the screen; (15) Remove the screen and place the CCD camera where the screen is located; (16) Adjust the focal length and exposure of the CCD camera to obtain clear interference fringes, capture the initial image, and measure the initial fringe spacing; (17) Turn on the DC power supply of the heating device to heat the copper tube. Wait for the image to stabilize every 5°C, capture the image once and measure the stripe spacing. The final interferometric image obtained by the linear expansion coefficient measurement system is as follows: Figure 7 As shown, Figure 7 Interference fringe pattern captured by a CCD camera.

[0075] In the above embodiments, adjusting the plane mirror is mainly to further investigate and eliminate the influence of minor errors and reduce interference noise. Adjusting the plane mirror is mainly to adjust its tilt angle to a suitable range.

[0076] The specific adjustment method is through the plane mirror bracket 2. The plane mirror bracket 2 includes a column, and an annular part is sleeved on the column. The annular part is sleeved on the column, and the inner diameter of the annular part is larger than the outer diameter of the column, so that there is a gap between the column and the annular part, so as to make fine adjustments to the angle of the plane mirror 3. After the adjustment is completed, it is locked with fasteners. An L-shaped connecting rod is provided between the annular part and the connecting arm. One end of the L-shaped connecting rod is fixedly connected to the annular part, and the other end is connected to the connecting arm 23.

[0077] In the above embodiment, the L-shaped connecting rod and the connecting arm 23 are integrally formed.

[0078] In this embodiment, an electric heating method is used to heat the copper rod, causing changes in the interference fringes of the Loewe mirror. A CCD camera captures the interference image, which is then processed using MATLAB. First, the interference fringe image undergoes grayscale conversion and Gaussian filtering to extract the fringe intensity. A vertical line is drawn on the interference image. Since the interference fringes are alternating bright and dark, the intensity distribution curve along this line exhibits a peak. The interference fringe intensity distribution diagram is shown below. Figure 8 As shown, the pixel distance between peak values ​​is calculated. Given that the actual distance corresponding to one pixel in the CCD camera used is 2 μm, the interference fringe spacing is pixel distance × 2 μm. The linear expansion coefficient of copper is then obtained from this.

[0079] The indoor temperature during the measurement was 25℃, and the spacing of the interference fringes was measured, as shown in Table 1.

[0080] Table 1. Average stripe spacing measured at various temperatures. In six temperature measurements, the temperature of the copper tube was displayed on an OLED screen and consistently reached 65°C. The positions of the measurement system and the CCD camera remained fixed throughout the experiment.

[0081] Using formula (12), the final elongation of the copper tube is calculated as shown in Table 2.

[0082] Table 2. Copper tube elongation measured at various temperatures Experimental data processing The current measurement = 428.5 mm, = 162.3 mm, = 60.0 mm, = mm, Taking the first set of data in Table 2 as an example, first calculate the average value of the variables: in, =1.87×10⁻⁵ .

[0083] Type A uncertainty: For Type B uncertainty, the determination is made by the Δmeter used as the measuring instrument. The ruler used in this experiment... Temperature sensor ℃.

[0084] The calculation yielded: According to the uncertainty propagation formula, we can obtain from formula (2) Relative uncertainty: As can be seen from equation (16), the error mainly comes from measuring the elongation of the copper tube.

[0085] The measurement results are as follows: The linear expansion coefficient of the brass tube provided by the manufacturer In comparison, the relative error can be obtained as follows: Therefore, the relative error of the measurement results is very small.

[0086] The use of Loewe mirror interferometry to study the linear expansion coefficient of materials is not only an innovation in linear measurement methods, but also improves the measurement accuracy of the linear expansion coefficient. By reasonably controlling and observing the temperature rise and ensuring the stability of the copper tube, the measurement method in this experiment reduces the influence of uncontrollable variables during the measurement process, greatly improving the measurement accuracy.

[0087] The above-disclosed embodiments are merely preferred embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A system for measuring the coefficient of linear expansion, characterized in that, include: Laser (1); A plane mirror bracket (2) is vertically arranged in the path of the horizontal beam emitted by the laser (1). A baffle (21) is provided on the top of the plane mirror bracket (2) near the laser (1). The baffle (21) is perpendicular to the beam. A plane mirror (3) is horizontally set on the top of the plane mirror bracket (2). One end of the plane mirror (3) abuts against the baffle (21), and the other end extends out of the plane mirror bracket (2). The material to be measured (10) is placed on the side of the plane mirror bracket (2) away from the laser (1). The material to be measured (10) abuts against the lower side of the plane mirror (3). The beam emitted by the laser (1) forms interference fringes with the beam reflected by the plane mirror (3) after passing through the plane mirror (3). A heating rod (4) is placed on the material to be measured (10). The material to be measured (10) expands due to heat and pushes the plane mirror (3) away from the baffle (21) to move upward, so as to adjust the angle of the plane mirror (3) and thus change the spacing of the interference fringes.

2. The linear expansion coefficient measurement system according to claim 1, characterized in that, The top of the plane mirror bracket (2) is provided with a horizontal support plate (22), which is connected to the plane mirror bracket (2). A baffle (21) is fixed on the edge of the support plate (22) near the laser (1).

3. The linear expansion coefficient measurement system according to claim 2, characterized in that, A connecting arm (23) is obliquely arranged between the plane mirror bracket (2) and the support plate (22). One end of the connecting arm (23) is fixedly connected to the plane mirror bracket (2), and the other end extends away from the laser (1) and is fixedly connected to the support plate (22).

4. The linear expansion coefficient measurement system according to claim 1, characterized in that, The baffle (21) has a notch (211) in the middle, through which the beam emitted by the laser (1) passes.

5. The linear expansion coefficient measurement system according to claim 1, characterized in that, Also includes: Temperature sensor (5) is fixed on the material to be measured (10).

6. The linear expansion coefficient measurement system according to claim 1, characterized in that, The material to be measured (10) is a tube. A copper tube support (24) is horizontally arranged on the side of the plane mirror support (2) away from the laser (1). The copper tube support (24) is connected to the plane mirror support (2). The tube is vertically arranged between the copper tube support (24) and the plane mirror (3) and abuts against them respectively. The heating rod (4) is arranged in the tube and fixedly connected to it.

7. The linear expansion coefficient measurement system according to claim 1, characterized in that, Also includes: A beam expander (6) is vertically positioned between the laser (1) and the plane mirror support (2), and the beam expander (6) is coaxial with the center line of the laser (1) emitting end.

8. The linear expansion coefficient measurement system according to claim 7, characterized in that, The focal length of the beam expander (6) is 45mm.

9. The linear expansion coefficient measurement system according to claim 1, characterized in that, Also includes: The light screen (7) is vertically positioned on the side of the plane mirror bracket (2) away from the laser (1).

10. The linear expansion coefficient measurement system according to claim 1, characterized in that, Also includes: A CCD camera (8) is used to acquire images of interference fringes.

Images