Rockwell Automation 2755-L7, -L9 Scanners - Manual (Page 20)

Chapter 3
Installation Considerations
3–7
For example, a 21 mil (.53mm) symbol with 0
°
pitch can be successfully
scanned at 27 inches (68.6 cm) with a Catalog. No. 2755–L7SC scanner. If
you pitch the symbol 30
°
and determine the adjusted minimum bar width
using the formula below, you will realize that you are attempting to read an
18 mil (.46 mm) symbol.
Adjusted Minimum Bar Width = Actual Bar Width
*
cos [pitch angle]
In our example, the following conditions apply:
Actual Bar Width = 21 mil (.53 mm)
Pitch Angle = 30
°
Therefore: 21
*
cos [30] = 18.2 mil (.46 mm)
The minimum recommended bar width that the L7SC can read is 20 mil (.54
mm). Because of the pitch of the symbol, you will have to use a different
scanner, such as the L7SD. However, you will also have to decrease the
distance between the scanner and the symbol. The Catalog No.
2755–L7SD’s maximum read range with a 18 mil (.46 mm) symbol is 24
inches (61 cm). The farthest element of the symbol including the quiet zone
must not exceed 24 inches (61 cm).
In summary, increasing the pitch of the symbol decreases the minimum bar
width. Figure 3.9 is an excerpt from Figure 2.2, which illustrates this
example.
Figure 3.9
Pitch Effecting Scan Range
2755–L7SA
2755–L7SB
2755–L7SD
21 mil (.53mm) long
symbol with 0
°
pitch
2755–L7SC
5
.13
25
.64
20
.51
15
.38
10
.25
Minimum Bar Width
Inches
Millimeters
5
12.7
Inches
Centimeters
10
25.4
15
38.1
20
50.8
25
63.5
30
76.2
35
88.9
Scan Range ( from scan window)
21 mil (.53mm) long
symbol with 30
°
pitch yields adjusted
minimum bar width
of 18 mil (.46mm).
Symbol to scanner
distance has also
been compensated so
symbol can be read
(see next page).