Motorola MK1200, Product Reference Manual

Page: 29 / 232

MK1200 Introduction 1 - 11
Ensure the symbol is in good condition.
Specular Reflection
When laser beams reflect directly back into the scanner from the bar code, they can “blind” the scanner and make
decoding difficult. This phenomenon is called 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. Practice
quickly shows what tolerances to work within.
Figure 1-9
Avoiding Specular Reflection
When scanning a 1D 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). However, the scanner is
not effective if its beams hit the bar code’s surface at an angle greater than 30
o
.
No specular reflection.
Decode can occur.
Side Views
Tilt Bar Code At Slight Angle (Up to 30°)
Ba
r C
od
e
Specular reflection.
Reflected beam is
within specular
dead zone and
prevents decode.
30
°
Ba
r C
od
e