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FACTORY RECALIBRATION REQUIREMENT
WHY DO CCD BASED VERIFIERS REQUIRE A FACTORY RECALIBRATION?
Axicon 6000, 6500 and 7000 verifiers all use linear CCD sensors to capture
scan reflectance profiles of barcodes. These CCD sensors work very much
like digital cameras in the manner in which they capture an image, but
they only image a single line scan across a barcode, similar to the scan
line that you see with a hand held laser scanner.
The accurate measurement of reflectance across the full width of the
scan relies on the barcode symbol being imaged as if the illumination
were perfectly uniform and the sensor element equally sensitive at all
points along the scan line. In practice this is not necessarily the case,
however, the electronics within the head of these units applies a function
that enables the units to perform as if this were the case, so that when
the scan reflectance profile reaches the PC or Macintosh computer the
application can make this assumption and proceed with analysis. To
achieve this, the heads need to undergo a factory calibration process.
This calibration is not the same as the calibration that is performed by
the software application on the computer. The calibration that occurs
within the application assumes that a uniform profile is already achieved
by the scanning head and simply shifts the overall signal so that the
maximum and minimum reflectance reading with a scan taken of a known
calibration, or reference test sheet gives the correct reading for that
sheet. This process is the user calibration.
After many thousands of hours of use, the intensity of the LEDs that
illuminate the barcode symbol will gradually change.