The Main Sensor Types and What Each One Measures
Selecting sensors requires matching physical transduction principles to measurands while accounting for thermal drift, noise floor, and fab availability.
Ndir Spectroscopy
Absorption Physics
Gas sensing technology utilizes the characteristic absorption of infrared light by specific molecular bonds to determine concentration levels. In ndir spectroscopy, a broad band light source passes through a gas sample toward a detector equipped with a narrow bandpass filter. The amount of light absorbed at the target wavelength corresponds directly to the density of the gas molecules present.
Optical Path
The sensor assembly consists of an infrared emitter, a sample chamber, a reference filter, and a thermopile or pyroelectric detector. Highly reflective internal surfaces maximize the interaction between the light and the gas by increasing the effective path length. A reference detector often monitors the source intensity at a wavelength where no absorption occurs to account for aging of the lamp.
Gas Selectivity
Molecular structures such as carbon dioxide or methane have unique spectral fingerprints in the mid infrared range. Because the optical filter only allows light at the specific absorption peak to reach the sensor, the system ignores other gases. This isolation allows for the measurement of specific concentrations in complex mixtures like ambient air or exhaust.
Calibration Drift
Contamination of the reflective surfaces or the optical windows reduces the signal strength over time. Regular zeroing with a nitrogen purge or a known fresh air sample maintains the accuracy of the readings. Automated compensation circuits adjust the detector gain to handle fluctuations in the source temperature.