12
Quick Reference
Specular Reflection
When laser beams reflect directly back into the scanner from the
bar code, they can “blind” the scanner and make decoding diffi-
cult. This is specular reflection.
To avoid this, scan the bar code so that the beam does not
bounce directly back. But don’t scan at too oblique an angle; the
scanner needs to collect scattered reflections from the scan to
make a successful decode. Simple practice quickly shows what toler-
ances to work within.
The Dead Zone
For scanning a 1-D bar code, there is only a small specular dead
zone to avoid (+ 2
o
from the direct laser beam). The specular dead
zone is larger for scanning PDF417 (+ 9
o
from the direct laser
beam). At the same time, the scanner is not effective if its beams
hit the bar code’s surface at an angle greater than 30
o
from the
normal to that surface.
Bar Code
Bar Code
Tilt Back At Slight Angle
(Up to 30
o
)
Avoiding Specular Reflection
