Design and fabrication of a mid-infrared carbon dioxide sensor for the application in greenhouse environment

Abstract

A mid-infrared carbon dioxide (CO2) sensor is presented for the application in greenhouse environment. An integrated multi-pass gas chamber and a dual-channel differential detection method are adopted to decrease response time and suppress environmental influence, respectively. An optical module is developed using a cost-effective wideband mid-infrared light source, a dual-channel pyre electrical detector and a spherical mirror, and the moisture-proof function is specially designed for enabling the application of this sensor in greenhouse with high humidity. Experiments are carried out to evaluate the sensing performance on CO2 concentration. According to the experimental results, the limit of detection (LoD) is about 3×10-5 with an absorption length of 30 cm. The relative detection error is less than 5% within the measurement range of 3×10-5—5×10-3. Based on 10 h long-term stability measurement on 5×10-4 and 2×10-3 standard CO2 samples, the maximum fluctuations are 1.08% and 3.6%, respectively. By using a 2.4 GHz wireless network communication system for remote monitoring and data recording, a field measurement of this sensor in a greenhouse is conducted, and good performance is proven in such circumstance.