Abstract: The automated selection of the best calibration for measuring selected physical, chemical or atomic properties of continuous moving sheets, or of a coating on the sheets, is provided by the use of an on-line qualitative multi-band infrared measurement of the material. The multi-band qualitative measurement produces a spectral pattern of the material, which is matched to a library of potential materials. Once the best spectral pattern match is selected, then the known calibration constant values are used to make quantitative measurements on selected properties of the sheet of material, or of a coating on the material. Typically, a property of interest is the weight per unit area (i.e., grams per square meter) of a plastic coating on a paper substrate. The automated selection may be done on a periodic basis to adapt to variations in the substrate material that would otherwise cause the quantitative measurements of the coating to become erroneous due to calibration errors.

Abstract: A scanning system including a source mounted on one side of a moving web and a detector on the other, and means for monitoring changes in the air temperature in the air gaps between the moving web and, respectively, the sensor and detector. The monitoring means comprises a thin sheet of a relatively opaque and inert material having a low thermal capacity and a low thermal conductivity, mounted closely adjacent one of the gaps and a thermopile mounted on the side of the sheet away from the gap for sensing the temperature of the sheet.In preferred embodiments in which the sheet is black polyester (e.g., "Mylar"), a sheet and thermopile are mounted on each of the sensor and detector housings, each sheet is mounted essentially coplanar with the inner side of the guide plate defining a respective air gap, and the respective thermopile is mounted on the side of its associated sheet opposite the gap.