Rockwell Automation 2755 StrataScan Bar Code Readers - Manual (Page 23)

3–2 Designing Your System
Publication 2755-6.13
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
The aspect ratio (symbol height to symbol length) cannot be greater
than 1.7:1 for Catalog No. 2755-LHR-3C and 2.5:1 for
Catalog No. 2755-LHR-5C.
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 specified 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, D or F assigned to the symbol. In
general, symbols are most decodable in the A range with diminishing
quality through F. An F or failure occurs because a symbol does not
conform to a legitimate bar code symbology, whereas a D grade has
a better chance of being read. And a C has a still better chance of
being read by more readers than a D. And so on.
Symbol Height and Length
Symbol Quality