Rockwell Automation 2755 Atomscan Bar Code Scanner - Manual (Page 26)

Chapter 3
Designing the System
3–15
Table 3.C
Cosines and Tangents for Various Pitch Angles
Use for Apparent Narrow Element Use for Lost Read Distance
Pitch Angle =
Θ
Cosine (
Θ
)
Pitch Angle =
Θ
Tangent (
Θ
)
0
5
10
15
20
25
30
35
40
45
50
1.0
.996
.985
.966
.940
.906
.866
.819
.766
.707
.643 0
5
10
15
20
25
30
35
40
45
50
0
.087
.176
.268
.364
.466
.577
.700
.839
1.
1.192
Step 2. The Read Range is further shortened by the lost Read Range: (the
distance of the far end of the symbol from the scanner) less (the distance of
the near end).
•
the far end must be within the scanner’s Read Range for the apparent
Narrow Element width
•
the near end determines the useable scan width. See Table 3.B for scan
widths at different distances from the scanner.
The loss of Read Range is calculated using this formula:
Lost Read Range =
Bar Code Symbol Length x Tan (Pitch Angle)
Table 3.C gives tan (30
_) = 0.577
3” x 0.577 = 1.7”
Figure 3.9
Read Range and Symbol Resolution at 0
_ and 30_ Pitch
Symbol’s Nearest and
Farthest Elements
7.0 inches (17.8 cm)
2755-L6SB
3 inch (7.6 cm) symbol
is pitched 0
_.
3 inch (7.6 cm) symbol
is pitched 30
°
.
Symbol’s Nearest
Elements
4.8 Inches (12.2 cm)
Symbol’s Farthest
Elements
2755-L6SB
Pitch (
Θ) =
0
_
Pitch (
Θ) =
30
_
6.5 inches (16.5 cm)