Rockwell Automation 2755 Atomscan Bar Code Scanner - Manual (Page 25)

Chapter 3
Designing the System
3–14
Example:
A 10 mil (0.25 mm) symbol including Quiet Zones is 3 inches (7.6 cm) long.
It is pitched at 30
_. What difference does this make in placing the scanner
and in reading the symbol?
Two factors reduce the Read Range of the scanner with respect to a pitched
symbol:
1. the apparent Narrow Element width is first used with Table 3.A or
Figure 3.6 to give the useable Read Range
2. the far end of the symbol (the end of the quiet zone) must be within the
Read Range as calculated in step 1, but the near end (the other quiet zone)
determines the effective distance from the scanner.
Step 1. With 0
_ pitch the symbol can be scanned at any distance between 2”
and 7” (5.1-17.8 cm) from the face of the scanner. With 30
_ pitch, the
apparent Narrow Element width is calculated using this formula:
Apparent Narrow Element Width =
Actual Element Width x Cosine (Pitch Angle)
Table 3.C gives cos (30
_) = 0.866
10 mils x 0.866 = 8.7 mils
Using Figure 3.6, for a Narrow Element width of:
•
10 mils, the Read Range is from 2.0” to 7.0” (5.1 to 17.8 cm)
•
8.7 mils, the Read Range is from about 2.2” to 6.5” (5.6 to 16.5 cm)
Figure 3.8
A Portion of Figure 3.6
5
10 .25
15
20 .50
5
12.5
10
25.4
Apparent Minimum Element W
idth
Inches
Centimeters
Read Range (from scan window)
1 0 2 3 4 6 7 8 9
Mils
(.001 in.)
mm
0 0
0 5.0 2.5 7.5 10.0 15.0 17.5 20.0 22.5
10 mil
8.7 mil
Losses due to
Step 1 Step 2 Step 1
Θ