Infrared instruments infer temperature from detected radiation. Clear, glossy, reflective, colored, textured, or masked sheets can produce different readings at the same true temperature. The sensor may also see radiation reflected from heaters or transmitted through the sheet.
The pyrometer’s wavelength range, emissivity setting, spot size, viewing angle, and target background should be evaluated for the specific material. A contact reference, calibrated black target, or another validated method may be needed during setup. Changing sheet color or protective film can invalidate a previous configuration.
Recipes should document the material-specific instrument settings and measurement location. A single emissivity value should not be copied across unrelated polymers and surfaces. Dirty optics and air-purge failure must be checked before recalibration.