Rockwell Automation 2755 High Performance VLD Scanner - Manual (Page 28)

3–15 Installation Considerations
You must consider the following when reading symbols that are
pitched:
•
The apparent minimum element width
•
The nearest and farthest code elements must be within the
scanner’s read range.
Determining Apparent Minimum Element Width
When a symbol is pitched, the bars appear to be narrower and closer
to one another. This apparent element width is a reduction of the
actual element width. Before positioning the scanner using the read
ranges in Figures 3.5 or 3.8, determine the symbol’s apparent
minimum element width.
Note: If the symbol has narrow spaces that are smaller than the
narrow bars, base the read range on the narrow spaces.
Figure 3.10 shows two boxes, each containing the same bar code
symbol. Below each box is an exaggerated view of 5 elements (3
black, 2 white) as seen from the top down.
Figure 3.10
Actual vs Apparent Element Width
30 _
Pitched 30 _
Actual Element Widths
10 mils
Apparent Element
Widths 8.6 mils
Apparent Element
Widths 10 mils
Actual Element Widths
10 mils
Apparent Element Width 10 mil (.25 mm)
0
_ Pitch
Apparent Element Width 8.6 mil (.22 mm)
30 _ Pitch
Compensating for
Pitched Symbols