InGaAs Sensor Selection for Foreign Matter Detection
Select standard InGaAs for cost-effective detection up to 1700 nm, or cooled extended InGaAs to capture 2200 nm polypropylene combination bands cleanly.
C-H Overtones
Spectral Signature
Molecular transitions define the harmonic frequencies observed in the near infrared range when analyzing organic polymers and natural fibers. These c-h overtones represent the secondary and tertiary vibrations of carbon-hydrogen bonds which appear at approximately 1200 to 1700 nanometers. Identifying these peaks allows high speed sorting systems to distinguish between cotton lint and synthetic polypropylene contaminants.
Accurate detection relies on the specific positioning of these peaks to differentiate between chemically similar materials such as polyester or polyethylene.
Molecular Resonance
Energy absorption occurs at specific intervals that correspond to the length and strength of the atomic bond. Because the fundamental vibration happens in the mid infrared region, these c-h overtones provide a weaker but measurable signal in the shorter wavelengths used by commercial scanners. High speed processors analyze the intensity of these signals to determine the chemical composition of a moving fiber stream.
This mechanism permits deeper penetration into a cotton tuft than surface level scans alone.
Detection Threshold
Signal strength decreases significantly with each successive harmonic level. Third c-h overtones are typically much fainter than the second, requiring highly sensitive indium gallium arsenide sensors to capture the data.
Sorting Application
Production lines utilize these specific spectral markers to trigger pneumatic rejecters. Real time analysis of c-h overtones ensures that white plastic fragments are removed from white cotton before the spinning process begins. This verification happens at the blowroom stage where fiber is most accessible.