Rockwell Automation 2755 Atomscan Bar Code Scanner - Manual (Page 24)

Chapter 3
Designing the System
3–13
When a symbol is pitched, the bars appear to the scanner to be narrower and
closer together than if it faced the scanner squarely. For pitched symbols, you
must allow for the following:
•
The apparent Narrow Element width, rather than the actual Narrow
Element width, must be used in determining the Read Range.
•
The nearest and farthest symbol elements must be within the scanner’s
Read Range.
Calculating Apparent Narrow Element Width
Determine the symbol’s apparent Narrow Element width before using the
Read Ranges in Table 3.A or Figure 3.6.
The exaggerated view of Figure 3.7 demonstrates the apparent Narrow
Element width concept. With a zero degree pitch angle, the scanner views the
actual Narrow Element width. When the symbol is pitched, the Narrow
Element appears smaller.
Figure 3.7
Actual vs Apparent Narrow Element Width
30 _
Actual Narrow Element Width
10 mils
Apparent Narrow Element Width
8.7 mils
Apparent Narrow Element Width
10 mils
Actual Narrow Element Width
10 mils
0 _ Pitch
30 _ Pitch
The apparent Narrow Element width is approximately the Cosine of the pitch
angle, multiplied by the actual Narrow Element width. From Table 3.C,
cos (30
_) is 0.866.
Compensating for
Pitched Symbols