Device for detecting characteristics of a moving paper web, said device comprising a polychromator and an IR detector matrix

An infrared detector device for detecting properties of a moving web of paper, the detector device comprising:

• a polychromator that receives light coming from the web of paper and an infrared detector with a matrix of infrared sensitive photoconductors arranged to receive light from the polychromator;
• an additional source of light arranged to uniformly illuminate the infrared detector, the source being controllably switchable on and off between a first light intensity and a second light intensity greater than the first light intensity, the source at least in its switched-off condition allowing unhindered passage of light along an effective beam path through the polychromator to the infrared detector;
• and
• an evaluation electronic unit connected with the matrix of the infrared detector, the evaluation electronic unit having a memory assigned to the photoconductors of the matrix, wherein the evaluation electronic unit is operable to:
• a) acquire electrical signals from every single photoconductor obtained at the first and at the second light intensity,
• b) use the thereby obtained electrical signals of a selected photoconductor as reference values,
• c) obtain, for every single photoconductor, based on the electrical signals thereof and the reference values, a first correction value and a second correction value, and
• d) store both correction values for every single photoconductor in the memory.