254764-001 Rev B 66
Calibration Hints
Calibration is used to normalize reflectance calculations to known (and/or traceable) values in absolute
units of % reflectance.
Calibration affects reflectance calculations only.
Calibration does not affect
any
other calculations or ability to decode a symbol, etc. The scanner gain and offset settings have the major
effect on scanning performance. Keeping the scanner signal linear (between the yellow lines as described in
the distance and angle setup sections above) is very helpful for good decoding, but is
CRUCIAL
for
reflectance measurements. The calibration procedure will not be successful unless the bar code signal is
proper.
There may be cases in applications where the material being analyzed requires a scanner gain and offset
setting that will not allow calibration with the standard SV calibration symbol. In most cases this is due to a
low contrast material (such as brown corrugated) that will make the signal level on the calibration symbol
go past the yellow lines. In cases like this there are two basic choices to make:
1.
Do not use parameters that involve absolute units of reflectance as failure criteria. These
parameters include Symbol Contrast, Overall ANSI Grade, PCS, Rmax, and Rmin.
2.
If reflectance parameters are required to be analyzed in the application, a calibration symbol can
be created from the material being analyzed. Contact PRINTRONIX Technical Support for details.
