Rockwell Automation 2755 High Performance VLD Scanner - Manual (Page 25)

3–12 Installation Considerations
Example 2:
Increasing the conveyor speed in Example 1 to 300 ft/min. decreases
the number of scans per symbol to less than 3. This means the
2755-LD4C1 scanner is no longer appropriate.
To increase the number of scans per symbol for picket fence
applications, you can do one of the following:
•
select a higher speed scanner
•
increase the usable beam length by backing the scanner away
from the bar code symbol
Selecting Higher Speed Scanner
The LD8C1 scanner has a scan rate of 500 scans/second. It reads 40
mil labels at a minimum distance of 10 inches. At 10 inches, the
LD8C1 has a usable beam length of 5.5 inches.
To calculate minimum scans per symbol, use these values:
A = 500 scans/second – 5% = 475 scans/second (minimum scan rate)
X = 5.5 inches
Y = 4.75 inches
Z = 60 inch/second (equivalent to 300 ft/min. )
S = 475 scans/second x (5.5 inches – 4.75 inches) / (60 inches / second)
S = 5.94 scans
Since S (scans per symbol) is greater than 5 and the application uses
good quality labels, the 2755-LD8C1 scanner is appropriate for this
application.
Increasing Usable Beam Length
The LD4C1 scanner at 10 inches produces a usable beam length of
8.1 inches. Minimum scans per symbol are now calculated using
these values.
A = 200 scans/second – 5% = 190 scans/second (minimum scan rate)
X = 8.1 inches
Y = 4.75 inches
Z = 60 inches/second (equivalent to 300 ft/min. )
S = 190 scans/second x (8.1 inches – 4.75 inches) / (60 inches / second)
S = 10.6 scans
Because of the increased scan angle of the LD4, some picket fence
applications can be performed with a higher number of reads using
the lower speed scanner.
Calculating Scans/Symbol