A CO2 sensor is a device that can measure the concentration of carbon dioxide(CO2) in a given volume of gas. They have wide applications from controlling indoor air quality to regulating airflow in mines. The concentration of CO2 can be calculated either chemically or using non-dispersive infrared method(NDIR). Modern CO2 sensors are compact-sized and use the NDIR method to find the concentration.

How does it Work?

An NDIR CO2 sensor has 4 important parts, the chamber, gas inlet and outlet valve, infrared(IR) lamp, and an IR detector. One end of the chamber has an IR lamp that produces IR rays within the absorption band of CO2 molecules. At the opposite end of the chamber, an IR detector is fixed to measure the intensity of the emitted rays. The inlet and outlet valves control the inflow and outflow of the gas.

The gas mixture is passed into the chamber through the inlet valve. The IR lamp then illuminates these particles and the residual IR rays reach the other end. IR detector at the other end captures these residual IR rays. The difference between the amount of light radiated from the lamp to the detected light at the IR detector accounts for the light absorbed light by CO2.

The difference in the light intensity is directly proportional to the number of CO2 molecules. Higher the concentration, the larger the difference. Modern CO2 sensor modules come with electronic circuitry that does the math all by itself. The final output is either an analog voltage signal or in digital form.

Modern Sensors and their Applications

The NDIR CO2 sensor breakthrough happened in 1993. The technology has improved since then. Modern CO2 sensors are equipped with very low power diodes. The chamber once used to be straight, whereas they are replaced by flexible waveguides now. The technological advancement in the field has helped the sensor in decreasing its size, & to be more reliable & sensitive.

Better design models are deployed in areas like mining, marine vessels & aerospace. They keep track of the concentration of carbon dioxide and control the inflow and outflow of air. They are also used in monitoring the CO2 concentration, and hence the breathing condition, in SCUBA diving & healthcare. Horticulture uses this technology to keep the plants properly aerated. Various other methods are also in the developing stage for a better design.

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