Operating principle of infrared spectroscopy
For compound identification purposes
All molecules supply characteristic absorptions in the infrared spectral range; based on these, molecules can be uniquely identified and differentiated from their environment. Historically regarded as a lab procedure only, during the previous decades infrared spectroscopy has transformed into an almost ubiquitous sensor technology, particularly when limited to the wavelength spectrum of the near infrared (800 nm to 2500 nm).
The underlying principle involves illuminating a sample with infrared radiation and analyzing the transmitted or backscattered light. The metrology system consists of a light source (e.g. halogen lamp in the near IR spectrum), a light refraction unit (optical filters, gratings), and an analysis unit (stand-alone or integrated into existing equipment).
For compound quantification purposes
The compound specific absorptions described above not only permit the measured compound to be differentiated from the substrate, but the intensity of the absorptions also allows conclusions to be drawn about the quantity of the absorbing compound – therefore facilitating contact-free thickness measurements.
This principle is employed for instance by our oil film gauge to measure oil coat thicknesses of oil plating on sheet metal, or our ice sensor to quantify icing on wind turbine blades or road surfaces.
The exact configuration of an individual compound identification or quantification system depends on the respective metrology task, and is individually developed by us.
Infrared spectroscopy measurements are by their nature non-destructive, and are performed cessentially ontact-free and within fractions of a second. This renders the method as highly advantageous for inspections of even sensitive processes or compounds. Relying on the near infrared spectrum permits the use of light transmitters for information transport over long distances and the use of cost-effective technologies.