Rockwell Automation 2755 AtomScan Bar Code Reader - Manual (Page 22)

3–2 Designing Your Scanner System
Publication 2755-6.9
The height is measured from one end of a bar to the other, and its
length is always the distance from one end of the symbol to the other,
including the Quiet Zones. A Quiet Zone is the empty space before
or after the bars, and is usually equal to 10 times the Narrow Element
Width.
Quiet Zones
Symbol Length = L
Symbol
Height = H
Quiet
Zones
L
H
A bar code reader cannot reliably read a poor quality symbol. Test
proposed bar code symbol samples to ANSI Standard X3.182-1990,
Bar Code Print Quality Guideline.
•
Low-cost verifiers that can test this standard are available from
several companies.
•
Symbol samples can be submitted to an independent symbology
testing company.
The ANSI guideline specifies six parametric tests plus two pass/fail
tests to determine the printed symbol quality. The tests result in an
overall letter grade of A, B, C, or FAIL assigned to the symbol.
•
Grade A printed symbols. Any reader should be able to read
them.
•
Grade B symbols. Many readers can read them, including
AtomScan
+ readers.
•
Grade C symbols. Symbols may appear to decode successfully,
but in production the performance may drop substantially.
Symbol Height and Length
Symbol Quality