A miniaturized carbon dioxide gas sensor based on infrared absorption

A miniaturized sensor for measuring carbon dioxide (CO2) gas concentration is developed based on infrared absorption. A novel space-double-beam optical probe is designed, which consists of an infrared source, an air chamber, an infrared receiving device, and two sapphire windows. The air chamber is modified by incorporating a parabolic-shaped receiving-light cone to effectively improve the signal-to-noise ratio of the sensor. Four rectangle holes are arranged around the air chamber, and diffusive sampling is adopted to collect gas into the air chamber. The infrared source works between ON and OFF states. The interference of background light is eliminated by subtracting the measured value in the ON state from the OFF state. The measurement model of the sensor is established based on the Lambert–Beer law and the working principle of the sensor. The partial least squares method is applied to calibrate the measurement model. The sensor has a volume of 80 mm (L)×78 mm (W)×35 mm (H), a weight of 200 g, a power consumption of 1.5 W, and a response time of 2.5 s. The experimental results show that the measurement accuracy of the sensor is 0.026% with a measurement range of 0–3% for CO2 gas concentration.