Calibrating High-Speed Spectroscopic Arrays for In-Line Polyolefin Film Contamination Detection
Calibrate high-speed InGaAs spectroscopic arrays using two-point reference standardization to detect and eject clear polyolefin film in blowroom chutes.
Two-Point Normalization
Sensor Alignment
Electronic calibration of optical sensors in fabric scanners adjusts the gain and offset of each individual pixel using two different reference levels. This procedure of two-point normalization utilizes a zero-reflectance dark scan and a high-reflectance white scan to scale the output of the sensor array. This calibration ensures that the entire width of the scanner produces a uniform output when inspecting fabric.
Baseline Correction
The adjustment establishes two fixed points for each photodetector, compensating for differences in pixel sensitivity and light source intensity across the scanning line. By subtracting the dark value and dividing by the white value, the system maps the output of each pixel to a scale of zero to one hundred percent. This correction eliminates the fixed-pattern noise from the resulting image.
Inspection Integrity
Automated inspection machines rely on this step to maintain high sensitivity to real yarn and shade defects during continuous runs. When a scanner is correctly normalized, even minor variations in fabric density or dye shade are detected. This high sensitivity is necessary for maintaining quality standards in fine cotton fabrics.
Method Limit
Contamination of the white and dark reference tiles with lint or dust can severely degrade the calibration. If the white tile is contaminated, the normalization calculation will generate an incorrect correction factor, causing artificial streaks in the fabric image. For this reason, the reference tiles must be kept clean and inspected regularly.