Picket Fence Calculation - Allen-Bradley 2755-LS7-SB User Manual

3–10 Designing Your Scanner System
Publication 2755-6.9

Picket Fence Calculation

To calculate scans per symbol for picket fence applications, use the
following formula.
R (W–L)
S =
C
S = Scans per Label
R = Scan Rate
W = Scan Width at the Minimum Read Distance
L = Symbol Length (including quiet zones)
C = Conveyor Speed
The –3 accounts for the incomplete scans at the beginning and end and one for the Automatic
Gain Adjustment.
Scan width, symbol length, and conveyor speed must be expressed in
similar units. The calculation assumes that the reader is triggered for
the entire time the symbol is present and the symbol has a 0° pitch.
Picket Fence Example
A bar code symbol is 2 inches long. The conveyor speed is 10
inches per second. The scan rate is 500 scans per second. The scan
width is 8 inches. Substitute in the following values to determine the
number of scans the bar code symbol will receive.
R = 500 scans/second
W = 8 inches
L = 2 inches
C = 10 inches/second
500(8 – 2)
– 3
10
– 3
= 297 scans