CN110686795A - Temperature measurement method of sapphire fiber in liquid metal based on ultrasonic principle - Google Patents

Abstract

The invention discloses a method for measuring temperature of sapphire optical fiber in liquid metal based on ultrasonic principle, and adopts a sapphire optical fiber temperature measuring device based on ultrasonic principle. The sapphire optical fiber temperature measuring device based on ultrasonic principle includes sapphire optical fiber ultrasonic sensor, ultrasonic pulse The detector and the computer data acquisition system are composed. The sapphire optical fiber ultrasonic sensor is connected with the excitation end of the ultrasonic pulse detector. The sapphire optical fiber ultrasonic sensor includes a sapphire optical fiber transmission rod. The sensitive area of the sapphire optical fiber transmission rod is provided with at least one radial groove at intervals. , the sensitive area of the sapphire optical fiber transmission rod is used for temperature measurement, the data end of the ultrasonic pulse detector is connected to the computer data acquisition system, and the laboratory static calibration of the sapphire optical fiber temperature measurement device is carried out to obtain sapphire at different temperatures from normal temperature to high temperature. The sound velocity value of the optical fiber propagation rod, and then real-time measurement of high-temperature molten liquid metal in actual situations.

Description

Temperature measurement method of sapphire fiber in liquid metal based on ultrasonic principle

technical field

The invention relates to the field of liquid high temperature temperature measurement, in particular to a temperature measurement method of a sapphire optical fiber in liquid metal based on an ultrasonic principle.

Background technique

With the continuous innovation of technology in the manufacturing industry, many liquid high temperature environments require accurate temperature testing. For example, the temperature test of molten aluminum, molten iron, and molten steel in the metallurgical industry, plasma temperature measurement in the electromagnetic field environment, etc., especially the status of aluminum alloy smelting technology in the manufacturing industry is becoming more and more prominent, and the temperature of molten aluminum directly affects aluminum. The quality and performance of castings are good or bad. Therefore, it is necessary to monitor the temperature of different locations in the smelting process for a long time. Due to the high temperature corrosiveness of molten aluminum, it can react with most metals. At present, the methods commonly used to measure the temperature of molten aluminum include k-type armored thermocouples and portable handheld infrared thermometers.

(1) Intermittent temperature measurement by k-type armored thermocouple: The thermode and insulating material are placed in a protected metal tube and pressed. During measurement, the front end is immersed in molten aluminum for temperature readings. Although this method is relatively simple, due to the strong corrosion of high-temperature molten aluminum and easy slag accumulation, it is easy to damage the protected metal tube, resulting in inaccurate measurement results and secondary pollution of molten aluminum, which cannot guarantee production quality. product quality.

(2) Hand-held portable infrared aluminum liquid thermometer: It is composed of an amplification system, a display system, a circuit system and an optical system. It mainly determines the temperature of the object by receiving the infrared radiation energy emitted by the object and converting it into a corresponding electrical signal. This method adopts non-contact measurement and the method is simple, but the measurement error is large, and the temperature value of the internal aluminum liquid cannot be accurately obtained.

Among them, the armored thermocouple can only perform short-term internal temperature point measurement, and multiple test points are required to distribute the temperature. The handheld infrared thermometer mainly uses the infrared temperature measurement technology to collect the thermal radiation energy on the surface of the molten aluminum, and cannot carry out the internal temperature test, and the results of the two measurements have large errors. At the same time, when monitoring the temperature of molten aluminum in real time, the high temperature and strong corrosiveness of molten aluminum must also be considered. Because molten aluminum can react with almost all metals and their oxides.

Therefore, it is urgent to design a new temperature sensor with high measurement accuracy and no secondary pollution to the molten aluminum, and can accurately measure the temperature distribution gradient inside the molten aluminum, so as to obtain aluminum with higher quality performance through casting. alloy.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for measuring the temperature of sapphire fiber in liquid metal based on the ultrasonic principle, which has high measurement accuracy and will not cause secondary pollution to the liquid metal.

In order to achieve the above object, technical scheme of the present invention is as follows:

A method for measuring temperature of sapphire optical fiber in liquid metal based on ultrasonic principle, and a sapphire optical fiber temperature measuring device based on ultrasonic principle. The sapphire optical fiber temperature measuring device based on ultrasonic principle includes sapphire optical fiber ultrasonic sensor and ultrasonic pulse detector. 2. It is composed of a computer data acquisition system. The sapphire optical fiber ultrasonic sensor is connected to the excitation end of the ultrasonic pulse detector. The sapphire optical fiber ultrasonic sensor includes a sapphire optical fiber transmission rod. The sensitive area of the sapphire optical fiber transmission rod is provided with at least one radial groove at intervals. The sensitive area of the optical fiber propagation rod is used for temperature measurement. The data end of the ultrasonic pulse detector is connected to the computer data acquisition system. First, the laboratory static calibration of the sapphire optical fiber temperature measurement device is carried out to obtain the sapphire optical fiber propagation at different temperatures from normal temperature to high temperature. The sound velocity value of the rod is then measured in real time for the high temperature molten liquid metal in the actual situation.

Further, the electrical signal of the ultrasonic pulse detector is converted into an ultrasonic signal through the transducer, which is transmitted to the sapphire fiber propagation rod from the excitation end for propagation, and is reflected back to the excitation end at the groove and the end face, and then the ultrasonic signal is transmitted to the excitation end. The signal is converted into an electrical signal and sent to the computer data acquisition system through the data terminal for subsequent signal analysis.

Further, the analysis of the signal is that the computer data acquisition system calculates the speed of sound value by calculating the time delay data between the echo signal generated at the radial groove and the end face reflected signal of the sapphire optical fiber propagating rod at different temperatures, Calculate the time-lapse data graph under different temperature values, so as to obtain the change curve of speed with temperature.

Further, there are two radial grooves, which constitute multi-distributed temperature measurement points.

Further, the distance between the radial groove position of the temperature sensitive area and the end face of the sapphire fiber propagation rod is called the reflection distance. When selecting the length of the reflection distance, the following relationship should be satisfied:

In the formula: ΔL—reflection distance; t ₁ —ultrasonic pulse excitation time; v(T)—ultrasonic wave speed; Δt—time difference.

Further, obtaining the sound velocity values of the sapphire optical fiber propagating rods at different temperatures from normal temperature to high temperature is obtained by obtaining the time-lapse data map at normal temperature -1600°C, and obtaining the relationship curve between temperature and time-lapse data by calculation. In practical application, according to v=2l/t, the obtained delay data calculates the speed, finds the relationship curve between temperature and sound speed, and then obtains the actual temperature.

In this case, the ultrasonic pulse temperature measurement technology is used to calculate the temperature value by measuring the delay data of ultrasonic waves in the sensitive material to obtain the speed of sound. That is, the signal waveform reflected from the groove and the end face is selected, and the delay data between the waveforms can be calculated by calculating the delay data. Obtain the sound velocity value at this temperature, and obtain the time-lapse data map under different temperature values, so as to obtain the change curve of the ultrasonic propagation velocity with temperature.

Description of drawings

Fig. 1 is the relation diagram of incident wave of the present invention, reflected wave and transmitted wave;

Fig. 2 is the schematic diagram of the sapphire optical fiber waveguide rod of the present invention;

3 is a schematic diagram of the acoustic wave propagation of the sapphire fiber multi-distribution ultrasonic sensor of the present invention;

Fig. 4 is the sapphire optical fiber temperature measuring device based on ultrasonic principle of the present invention;

Fig. 5 is the molten aluminum laboratory static calibration temperature measurement system of the sapphire optical fiber temperature measurement device based on the ultrasonic principle of the present invention;

6 is a waveform diagram of time-delayed data from normal temperature to 1600° C. of the sapphire optical fiber temperature measuring device based on the ultrasonic principle of the present invention;

Fig. 7 relation curve of the time delay data and temperature of groove one, groove two of the sapphire optical fiber propagating rod of the present invention;

Fig. 8 is the relation curve of temperature and sound velocity of groove one, groove two of the sapphire optical fiber propagating rod of the present invention;

Fig. 9 is a temperature change curve of the sapphire optical fiber temperature sensor of the present invention inserted into molten aluminum liquid for process 1 measurement.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Ultrasonic temperature measurement technology obtains temperature information by testing the speed of ultrasonic propagation in liquid. This ultrasonic sensor material must have good thermal conductivity and sound transmission, and can quickly reach thermal equilibrium with the temperature measurement liquid. We call this material a temperature sensitive material, usually some metal wires, metal rods, single crystal materials, etc. are used. In this case, a sapphire optical fiber drawn from alumina single crystal was selected as the sensitive material in combination with the high temperature corrosion characteristics of molten aluminum.

As shown in FIG. 4 , the present invention designs a sapphire optical fiber temperature measurement device based on the ultrasonic temperature measurement principle, comprising a sapphire optical fiber ultrasonic sensor 1, an ultrasonic pulse detector 2, and a computer data acquisition system 3. The sapphire optical fiber ultrasonic sensor is formed. The sensor 1 is connected to the excitation end 21 of the ultrasonic pulse detector 2. The sapphire optical fiber ultrasonic sensor 1 includes a sapphire optical fiber propagation rod 11. At least one radial groove 12 is arranged on the sensitive area of the sapphire optical fiber propagation rod 11. The sapphire optical fiber propagation rod The sensitive area 11 is used for temperature measurement, and the data terminal 22 of the ultrasonic pulse detector 2 is connected to the computer data acquisition system 3 .

The working principle of this case is that, as shown in Figures 1 and 4, the electrical signal of the ultrasonic pulse detector 2 is converted into an acoustic signal through a transducer (not shown in the figure), and is transmitted to the sapphire through the excitation end 21 The optical fiber propagation rod 11 propagates, reflects back to the excitation end 21 at the groove 12 and the end face 13, and then converts the acoustic signal into an electrical signal through the data end 22 and sends it to the computer data acquisition system 3 for subsequent signal analysis; the signal The analysis is that the computer data acquisition system 3 calculates the sound velocity value by calculating the time delay data between the echo signal generated at different temperatures and the radial groove 12 and the reflected signal from the end face 13 of the sapphire fiber propagation rod 11, and then calculate Obtain the time-lapse data graph under different temperature values, so as to obtain the change curve of speed with temperature.

As shown in Figures 2, 3, and 4, there are two radial grooves, namely groove one 121 and groove two 122, which constitute multi-distributed temperature measurement points. The signal is converted into an acoustic signal 41 through a transducer (not shown in the figure), which is transmitted to the sapphire fiber propagation rod 11 from the excitation end 21 for propagation, and the reflected wave 43 of the groove two is generated at the groove two 122. The groove one reflected wave 42 is generated at the groove one 121, and the end face reflected wave 44 is generated by the end face 13. The groove one reflected wave 42, the groove two reflected wave 43, and the end face reflected wave 44 are reflected back to the excitation end through the sapphire fiber propagation rod 11 21. The ultrasonic pulse detector 2 converts the acoustic signal into an electrical signal and sends it to the computer data acquisition system 3 through the data terminal 22 for subsequent signal analysis. The analysis of the signal is that the computer data acquisition system 3 calculates the echo signals generated by groove 2 122 and groove 1 121 at different temperatures. The groove 2 reflected wave 43, the groove 1 reflected wave 42 and the sapphire fiber propagation rod The end face 13 of 11 reflects the time delay data between the end face reflected waves 44 of the signal, calculates the sound speed value, and calculates the time delay data map under different temperature values, so as to obtain the multi-distributed temperature measurement point velocity change curve with temperature, so that More conducive to temperature measurement analysis.

As shown in Fig. 3, the distance between the radial groove position of the temperature sensitive area and the end face of the sapphire fiber propagation rod is called the reflection distance, and the distance between the second groove 122 and the first groove 121 is called the reflection distance. The reflection distance ΔL 1, the distance between the groove one 121 and the end face 11 is called the reflection distance ΔL2, and the size of the reflection distance has an important influence on the ultrasonic temperature measurement: the reflection distance is too large, through the groove two 122 and groove one The delay data between 121 and the waveform reflected by the end face 11 is too large. Although it is beneficial for analysis, the length of the temperature sensitive area increases. Since the temperature measured by the sapphire fiber ultrasonic sensor is the average temperature of the length of the sensitive area, the longer the temperature measurement area, the lower the temperature measurement accuracy, and the temperature gradient cannot be measured. Recognition; on the other hand, if the reflection distance is too small, the waveforms and secondary echoes reflected by groove 2 122, groove 1 121 and end face 11 will be superimposed together, which cannot be accurately identified, which will bring great impact to the analysis data. Big trouble. Therefore, in combination with the above description, when selecting the length of the reflection interval, the following relationship should be satisfied:

In the formula: ΔL—reflection distance; t ₁ —ultrasonic pulse excitation time; v(T)—ultrasonic wave speed; Δt—time difference.

The sapphire optical fiber propagation rod in this case is made of aluminum oxide (Al ₂ O ₃ ) single crystal, and has the characteristics of stable structure, high melting point (2053°C), and good thermal conductivity. Therefore, the sapphire fiber temperature measurement device based on the ultrasonic principle is used to measure the temperature in the liquid metal. First, the laboratory static calibration of the sapphire fiber temperature measurement device is carried out to obtain the sound velocity of the sapphire fiber propagation rod at different temperatures from normal temperature to high temperature. Real-time measurement of high temperature molten liquid metal in practical situations.

For example, the sapphire optical fiber temperature measuring device based on ultrasonic principle is used to measure the temperature in liquid metal, and the sapphire optical fiber propagation rod made of alumina (Al ₂ O ₃ ) does not react with molten aluminum. Before measuring the temperature of molten aluminum, it is necessary to carry out a static calibration experiment to check the sensor waveform amplitude, time delay data, structural performance stability, etc.

As shown in Figures 2, 3, 4, and 5, the laboratory calibration data in this case was obtained from normal temperature to 1600 °C. The 1600 °C high temperature resistance furnace 5 was used for data calibration, and double rows of silicon molybdenum rods were used in the furnace for heating. , the surrounding area is insulated with high-temperature refractory bricks to form a temperature zone of 100×100×100mm. During the heating time process, it is set to maintain at an integer temperature point for 5 minutes, so the internal temperature zone can be approximately regarded as a constant temperature field. The sapphire optical fiber propagation rod 11 of the sapphire optical fiber temperature sensor 1 is placed in a constant temperature field together with a standard platinum-rhodium thermocouple, and data is collected and recorded once every time the thermocouple changes by 100°C. When the distance between the groove two 122 and groove one 121 of the sapphire optical fiber propagation rod 11 is constant from the end face, the thermal expansion effect of the optical fiber temperature sensor itself can be almost ignored, and the groove two 122 and groove one 121 at different temperatures are collected. The reflected waveform can have a certain relationship between the time delay data between groove two 122 and groove one 121, groove one 121 and end face 13 and the temperature value in the current state. By calibrating the time delay data, the time delay data map of normal temperature -1600°C (high temperature) is obtained (as shown in Figure 6), and the relationship between temperature and time delay data is obtained by calculation (as shown in Figure 7), according to Figure 7 According to the time-delay data at different temperatures, the relationship between temperature and speed of sound can be calculated according to v=2l/t (as shown in Figure 8).

As shown in Figure 8, the high temperature resistance furnace is used for calibration, and the internal temperature field is considered to be uniform and constant, that is, the temperature data of groove 1 and groove 2 obtained by the sapphire fiber temperature sensor in the temperature region of 100 × 100 × 100 mm It is the same, the curves of temperature and speed of sound should basically coincide. Therefore, the relationship between temperature and sound velocity obtained by static calibration experiment is basically consistent with the theoretical calculation data, and it also verifies the feasibility of the sapphire fiber temperature sensor to measure temperature.

Finally, the temperature of molten aluminum was measured in real time with a calibrated sapphire optical fiber temperature sensor, and the results were analyzed.

In the actual temperature measurement process, the sapphire optical fiber transmission rod of the sapphire optical fiber temperature sensor needs to be inserted into the molten aluminum liquid for measurement, and the minimum temperature of aluminum in the molten state is about 640 ℃. The aluminum alloy resistance furnace used in this case has the highest temperature The upper limit temperature can reach 740 ℃, and its temperature change process is not large. In the actual temperature measurement process, two process temperature tests are carried out. Process 1: The sapphire optical fiber propagating rod is inserted into the molten aluminum in the lowest molten state to reach thermal equilibrium, and the data is continuously collected to obtain the time response speed curve of the sapphire optical fiber temperature sensor; in addition, multiple single-point test temperature values in this state are also carried out. ; Process 2: The temperature value is set to the upper limit threshold through the control cabinet, and the heating process of molten aluminum is continuously collected. Since this process is heated by means of furnace wall-air-dry pot heat exchange, the heating process is relatively slow. It is necessary to carry out continuous data acquisition for a long time to obtain the heating curve of temperature over time, and to perform multiple single-point temperature measurements on the molten aluminum at the highest temperature value.

After the temperature measurement of the molten aluminum is carried out according to the above-mentioned temperature measurement process 1, the data results are analyzed and analyzed to obtain the temperature change curve with time as shown in Figure 9. After the rod was inserted into the molten aluminum, the temperature began to rise rapidly. After 43.8s, the temperature value of the sapphire fiber temperature sensor reached the maximum peak value of 635 °C for the first time, and then with the further increase of time, the temperature value basically maintained a horizontal fluctuation. In addition, from the temperature rise curve in Figure 9, it can also be concluded that the sapphire fiber temperature sensor reaches the thermal equilibrium state 43.8s after being inserted into the molten aluminum liquid.

Since molten aluminum transfers heat through heat exchange, it can be seen from the experimental data in Fig. 9 that there is a temperature gradient difference between the two sensitive areas of groove 1 and groove 2 in the longitudinal direction of the molten aluminum. Among them, the position of groove 1 is closer to the bottom of the dry pot, and the temperature value measured after heat balance is higher; groove 2 is closer to the liquid level of aluminum liquid, and the temperature is relatively lower, which shows that the temperature rises during heat exchange. , the temperature distribution inside the molten aluminum is not uniform.

After the first process is completed, the second process is performed again. By adjusting the rated temperature value of the control cabinet, the temperature of the molten aluminum in the dry pot continues to rise with time. After about 15 minutes, the temperature reaches 734°C (the upper limit of the temperature of the control cabinet is 740°C, and if it continues to increase, the control cabinet will be damaged due to excessive power). Moreover, after the sapphire optical fiber propagation rod was measured in molten aluminum for a long time, the waveform amplitude did not change, and there was no corrosion trace on the surface of the optical fiber in the temperature sensitive area. It can be seen that the sapphire fiber temperature sensor based on the principle of ultrasonic temperature measurement can be used as a new method to measure the temperature of molten aluminum.

The sapphire fiber temperature sensor designed according to the principle of ultrasonic temperature measurement in this case can not only be used in the temperature measurement of molten aluminum, but also because sapphire fiber itself has the characteristics of high melting point (2053℃), high temperature oxidation resistance, and electromagnetic interference resistance, it can be used for more Conduct temperature test studies on multiple occasions. For example, temperature testing of molten iron and molten steel in metallurgical industry, plasma temperature measurement in electromagnetic field environment, etc., will have broader research value and significance in the future.

The above are only specific embodiments of the present invention, and do not limit the protection scope of the present invention. All equivalent changes made according to the design ideas of this case fall into the scope of protection of this case.

Claims (6)

1. the temperature measurement method of the sapphire optical fiber based on the ultrasonic principle in liquid metal, it is characterized in that: adopt the sapphire optical fiber temperature measuring device based on the ultrasonic principle, the described sapphire optical fiber temperature measuring device based on the ultrasonic principle, comprises the sapphire optical fiber ultrasonic sensor , an ultrasonic pulse detector, and a computer data acquisition system. The sapphire fiber ultrasonic sensor is connected to the excitation end of the ultrasonic pulse detector. The sapphire fiber ultrasonic sensor includes a sapphire fiber propagation rod. The sensitive area of the sapphire fiber propagation rod is spaced with at least one diameter. To the groove, the sensitive area of the sapphire optical fiber transmission rod is used for temperature measurement, and the data end of the ultrasonic pulse detector is connected to the computer data acquisition system. The sound velocity value of the sapphire optical fiber transmission rod at the temperature is measured in real time for the high temperature molten liquid metal in the actual situation. 2. the temperature measuring method of the sapphire optical fiber in liquid metal based on ultrasonic principle as claimed in claim 1, it is characterized in that: the electrical signal of described ultrasonic pulse detector converts electrical signal into ultrasonic signal through transducer, The excitation end is transmitted to the sapphire fiber propagation rod for propagation, and reflected back to the excitation end at the groove and the end face, and then the ultrasonic signal is converted into an electrical signal and sent to the computer data acquisition system through the data end for subsequent signal analysis. 3. the temperature measuring method of the sapphire optical fiber in liquid metal based on ultrasonic principle as claimed in claim 2, it is characterized in that: the analysis of described signal is that computer data acquisition system generates by calculating radial groove place under different temperatures The time delay data between the echo signal and the end face reflected signal of the sapphire optical fiber propagating rod, the sound speed value is calculated, and the time delay data map under different temperature values is calculated to obtain the change curve of speed with temperature. 4 . The method for measuring temperature of sapphire fiber in liquid metal based on ultrasonic principle according to claim 1 , characterized in that: there are two radial grooves, which constitute multi-distributed temperature measuring points. 5 . 5. The temperature measurement method of sapphire optical fiber in liquid metal based on ultrasonic principle as claimed in claim 1, it is characterized in that: the radial groove position of described temperature measurement sensitive area is between the sapphire optical fiber propagation rod end face The distance is called the reflection distance. When choosing the length of the reflection distance, the following relationship should be satisfied:

In the formula: ΔL—reflection distance; t ₁ —ultrasonic pulse excitation time; v(T)—ultrasonic wave speed; Δt—time difference. 6. the method for measuring temperature of sapphire optical fiber in liquid metal based on ultrasonic principle as claimed in claim 1, it is characterized in that: described obtaining the sound velocity value of the sapphire optical fiber propagating rod of different temperature from normal temperature to high temperature, is obtained by obtaining The time delay data map of normal temperature - 1600 ℃, the relationship between temperature and time delay data is obtained by calculation. In practical application, the speed is calculated based on the delay data obtained by v=2l/t, and the relationship between the temperature and the speed of sound is searched to obtain the actual temperature.

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