About Sources for NDIR Sensor
NDIR sensors are typically thermopile sensors. The sensor generate an output (voltage or current) that is proportional to the amount of light (heat) that reaches the sensor. Sensors are available with very small active areas of approx .36 mm² however most NDIR sensors use a larger area of 2 mm² or even 4 mm² areas. Packages are available in SMD to small TO-46 and TO-39.
NO Module NDIR Infrared Nitric Oxide Module Gas Sensor
Nondispersive infrared (NDIR) spectroscopy is often used to detect gas such as carbon dioxide, nitrogen dioxide, sulfur dioxide, etc., and measure the concentration levels. In high concentrations these gasses can be lethal or explosive, making the monitoring for these gasses imperative in certain environments.
The technique is said to be nondispersive because no dispersive elements (e.g a prism or diffraction grating) are used and the wavelength that passes through the sampling chamber is not pre-filtered.
The majority of NDIR sensors use a broadband light source, a gas chamber with highly reflective walls, optical filter(s), detector(s), and electronics for signal processing. Absorption of infrared light occurs at the IR energy (i.e. wavelength) specific to the target gas, which means it is high selectivity to a specific gas which is key to NDIR gas detection
How Sources for NDIR Gas Sensors Work
When infrared radiation interacts with gas molecules, infrared light is absorbed by the gas molecules at a specific band or wavelength, causing vibration of the gas molecules and absorption. The ratio of transmitted radiation energy to the incident energy reaching the detector, is dependent on target gas concentration. NDIR gas sensors detect the decrease in transmitted infrared light which is in proportion to the gas concentration.
Single vs Dual sensing gas sensing designs
The level of infrared light that the detector receives plays an important role in sensor drift and measurement accuracy. The infrared light source will have degradation of illumination over time from film buildup and age. There are also environmental factors to consider. The effects of temperature on an NDIR sensor are complex and care must be taken as changes in temperature reflect the absorbance, SPAN and apparent gas concentration.