Abstract: This paper introduces the measurement principle, design, fabrication, and experimental results of a novel infrared temperature sensor. Its basic mechanism utilizes a high-precision infrared displacement sensor to measure the length of an acrylic glass element with a large coefficient of thermal expansion that changes with temperature. We calibrated it using a high-precision quartz thermometer with a sensitivity of 0.001℃. The temperature measurement accuracy of this instrument can reach the order of ℃. Compared with existing temperature sensors on the market, it has significant advantages in sensitivity and linearity, and has broad application prospects. 1. Introduction In physical experiments and actual production, high-precision measurements are often required. Ambient temperature is a crucial factor in measurement. Therefore, precise measurement of ambient temperature is essential. Measuring instruments should also meet the following requirements: low manufacturing cost, high measurement accuracy, good linearity, wide application range, and ease of installation and debugging. Currently, various sensors are available for temperature measurement. Commonly used sensors include quartz thermometers, fiber optic thermometers, and thermistor thermometers. Among these devices, quartz thermometers have the highest sensitivity, currently reaching the order of ℃. However, these sensors are generally quite expensive. Linearity is difficult to achieve to meet the requirements of precision measurement. This paper aims to develop a high-precision infrared temperature measuring instrument. We know that infrared light has good monochromaticity and anti-interference properties, making it suitable for high-precision measurement. The instrument we design has a simple structure, is easy to manufacture and install, and can perform high-precision temperature measurements. The temperature measurement data can be directly output to a microcomputer or PC for subsequent data processing, which is very convenient and easy to implement. 2. Instrument Principle and Application We use microcrystalline glass-ceramic material produced by Beijing Donglinsong Industry and Trade Co., Ltd. to make a cylinder. This microcrystalline glass-ceramic material has good vacuum properties, resistance to high and low temperatures, insulation, and resistance to acid and alkali corrosion. Its basic performance indicators are as follows: operating temperature -273℃～1000℃, volume resistivity 1.08 x 10¹⁴ Ω·cm, coefficient of thermal expansion αl = 8.6 x 10⁻⁶/℃. Microcrystalline glass-ceramic has excellent thermal shock resistance; it does not break when rapidly cooled from 800℃ to 0℃, and its strength does not change when rapidly cooled from 200℃ to 0℃. A thin acrylic cylinder, L=10cm long, is fixed at one end inside the tube, and an infrared displacement sensor is fixed at the other end. The free end of the acrylic rod partially obscures the receiving surface of the infrared receiver tube, ensuring it operates in the region of optimal linearity. Since the coefficient of thermal expansion of acrylic is α2＝1.7 x 10⁻⁴/℃, a difference of two orders of magnitude, the relative displacement of the acrylic on the ceramic card material can be considered negligible when the temperature changes. Therefore, the change in the relative position between the free end of the acrylic and the infrared displacement sensor will alter the effective receiving area of ​​the infrared receiver tube, thus changing the output voltage of the displacement sensor. The measurement sensitivity of this novel temperature sensor is: ΔT=ΔL/L（α1-α2） where ΔL is the sensitivity of the infrared displacement sensor to measuring the length of the acrylic. The infrared displacement sensor mainly consists of an infrared LED emitting and receiving device, a data amplification and noise reduction section, and a data acquisition and processing system. We can see that it utilizes the photoelectric conversion law of infrared photodiodes, determining the blocking body through the relationship between the luminous flux blocked and the output current. It can convert minute temperature changes into voltage changes. These changes are then amplified using an amplifier circuit. A functional relationship between voltage and temperature is established using a data acquisition card. Finally, calibration is performed using a high-precision micrometer, resulting in a displacement measuring instrument with high measurement accuracy (3×10⁻⁷ m). Because the photoelectric conversion current is small and the power of the infrared LED is also low, we can assume that the infrared displacement sensor will not affect the measured temperature environment. 3. Instrument Construction and Experimental Results We placed the designed temperature sensor and a quartz thermometer with a sensitivity of 0.001℃ into a copper box, keeping them as close as possible to minimize the difference in ambient temperature. A 1W bulb encased in a black box was placed inside to heat the box. The black box was used to reduce the influence of background light on the infrared displacement sensor. Data acquisition in the experiment was performed using a PCL-71IB data acquisition card. The PCL-711B is a high-performance, high-speed, and multifunctional data conversion card compatible with current IBM PCs or other compatible computers. Its high performance, rich software support, and diverse functions make the PCL-71IB an ideal choice for industrial applications and experimental equipment. We utilize its A/D conversion function combined with serial communication to input data into a PC for post-processing. In the experiment, we turned on the bulb with a control power of 1W, reaching 60℃ after approximately 25 minutes. Due to the rapid heating process, we selected the cooling process for measurement. The temperature reached 50℃ after approximately 30 minutes and reached room temperature (28℃) after 2 hours. Because the voltage change corresponding to temperature changes is quite drastic, the temperature range for measurement was controlled between 40℃ and 39.905℃. Each time the quartz thermometer reading changed by 0.005℃, the corresponding voltage data was read. The final voltage data and the measured temperature of the quartz thermometer are shown in Table 1. Table 1 Temperature-Voltage Measurement Data [img=416,213]http://www.e-works.net.cn/images/128024312118437500.gif[/img][/align] From the data in Table 1, we performed linear fitting, and the curve and fitting equation results are as follows: The linear fitting equation is: T=39.949+（-0.00926）＊V, R=-0.99863. As shown in Figure 2, the linearity is quite good, although there are small fluctuations in some areas. The sensor sensitivity is: k＝ΔLT／ΔLV＝9.26×10⁻⁵℃/mV. Compared with other existing temperature sensors, we can see that its sensitivity is an order of magnitude lower than that of a quartz thermometer. Moreover, its linearity is relatively good. Structurally, the device is relatively simple, low in cost, and widely applicable, and it is particularly suitable for environments requiring precise temperature measurement. [align=center][img=277,253]http://www.e-works.net.cn/images/128024312319375000.GIF[/img] Figure 1. Structure diagram of the whole leaf experimental device[/align][align=center][img=291,251]http://www.e-works.net.cn/images/128024312485625000.GIF[/img] Figure 2. Temperature-voltage fitting curve[/align][align=left] 4. Summary From the entire design and implementation process of the sensor, we found that the complexity of the selected materials and the stability of the performance index had a certain impact on the experimental results. However, in the future, we will select new materials with good linearity and high coefficient of thermal expansion. We have reason to believe that the accuracy of this new infrared temperature sensor will be further improved. Of course, on the other hand, due to the resolution limitation of the displacement sensor, this new temperature sensor still has some shortcomings in environments with large temperature changes. However, for our commonly used working and experimental environments, it can completely replace the traditional thermometer. From this perspective, its application prospects are quite broad.