Results and Discussions The calibration results of the sensor under different temperatures and different concentrations of standard gas are shown in Fig. 7. It can be observed that the temperature affects the peak-to-peak value difference d₁, which in turn affects the gas concentration value of the sensor. And it can be noted that the temperature affects the peak-to-peak value difference approximately linearly. By fitting the temperature and the peak-to-peak value difference d₁, the formula for calculating the compensated difference d can be obtained, as shown by Eq. (9). The relationship between the compensated difference d and standard gas concentration C can then be obtained, as shown in Fig. 8. The fitting curve of CO₂ concentration with temperature compensation is obtained by refitting the data. In order to verify the accuracy of the fitting curve, retest is carried out at different temperatures and different concentrations. The data are shown in Table 1. The retest results show that the sensor can measure the gas concentration of 0%-5% in the temperature range of 0-40 ℃, and the error is less than 0.1% for the concentration of 0%-2%, and less than 0.25% for the concentration of 2%-5%.

CO₂ gas sensor is a key device in industrial control, medicine and health protection. Gas sensor based on infrared absorption principle has the outstanding advantage of high selectivity, but it faces the problems of low integration, large size, and low precision. In recent years, with the efforts of major research institutions and universities, the design of infrared sensors is developing rapidly, but it is urgent to solve the limitations of poor sensitivity and small detection range of the sensors. In this paper, a miniaturized non-dispersive infrared CO₂ sensor with the design of dual-band single-gas-channel structure is proposed, which is based on the infrared pyroelectric effect. The temperature compensation technology of the sensor is explored by the standard gas calibration method. The output values of the detector at different concentrations and temperatures are measured, and the relationship among the temperature, CO₂ concentration and output value of the detector is established. Software algorithm is used to realize the temperature compensation function, so as to realize the accurate measurement of gas concentration in different environments.

The infrared CO₂ sensor is composed of four main parts: infrared light source, air chamber, dual-channel pyroelectric detector, and main circuit system, as shown in Fig. 2. In order to realize the miniaturization of the sensor while maintaining high performance, a C-type multi-reflection air chamber structure is designed to increase the optical path and ensure the length of the interaction between light and gas. Through modular integrated design, a miniaturized air chamber with a height of 8 mm and a diameter of 18 mm is obtained, which minimizes the volume of the sensor. Finally, a miniature infrared CO₂ gas sensor with a diameter of 23 mm and a height of 10 mm is realized. The single-optical-path dual-wavelength differential design concept can effectively eliminate the interference of the air chamber, the light source and impurities, and reduce the influences of environmental temperature, dust, moisture and other factors on the system, thereby reducing the measurement error and improving the measurement accuracy of the system. Both hardware circuits and software programs adopt modular design to reduce system coupling. In order to ensure the accuracy and detection range of the sensor, the method of calibrating the sensor by standard gas concentration is used to build a sensor calibration experimental platform, as shown in Fig. 6, which mainly consists of a high and low temperature humidity test chamber, a standard gas source, and a sensor fixture. During the calibration process, the temperature is first set at 0 ℃, and pure nitrogen is introduced after the sensor output is stable. It can be considered that the concentration of carbon dioxide in pure nitrogen is 0%, that is, the zero point. After 5 min of ventilation, the voltage values collected by the microcontroller are saved for data fitting. Then, carbon dioxide with concentrations of 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, and 5% is introduced in sequence. After the calibration is completed at 0 °C, the ambient temperature in the high and low temperature humidity test chamber is set to 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, and 40 ℃, respectively, and the calibration is completed in the same way. The peak-to-peak values, temperatures and concentrations of the two channels are recorded.

In this paper, a miniature non-dispersive infrared CO₂ sensor based on infrared pyroelectric effect is designed and implemented. The temperature compensation of the sensor is realized by calibrating the sensor with standard gas concentration, and the sensor can perform accurate measurement at different temperatures and different concentrations. The sensor achieves a miniaturized design with a diameter of 23 mm and a height of 10 mm, and can realize accurate measurement with the error less than 0.1% at 0%-2% concentration and less than 0.25% at 2%-5% concentration. It can provide core devices and technical support for CO₂ concentration monitoring in industrial manufacturing, production and living environments, and has important practical significance for ensuring safe production and human health.