Appendices
A-12
MS-850 Raster Scanner User’s Manual
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Raster Picket Fence Calculation
For raster picket fence scanning, the number of decodes
(ND) is calculated in two formulas, one for sweep rate and
the other for number of decodes.
Sweep Rate.
Since the speed of the raster (SwR) cannot exceed 30, you
first need to ensure that you can achieve this by solving for
sweep rate (SwR). Sweep rate is the number of raster
sweeps (up or down) that occur in a second. Sweeps per
second should generally be as few as possible in order to maximize the number of
decodes applied to a given label.
The formula for finding
Sweep Rate
(SwR) is as
follows:
1
SwR
(Sweep Rate) is the number of passes, up or down, that are described by the arc
of the raster mirror.
LS
(Label Speed) is the distance per second that a symbol moves through the scan.
SW
(Scan Width) (picket fence formula only) is the width across the scan beam, at a
given distance from the scanner, in which a label can be read.
LL
(Label Length) (picket fence formula only) is the length of the longest printed label
to be read plus the length of the quiet zones.
Example:
Important
: The maximum sweep rate that your can set the scanner for is 30. If
your solution is greater than 30, you must change another parameter such as label
speed, etc.
Since SwR can only be entered into the software as whole numbers, round off frac-
tions of SwR to the next higher number, for example enter 0.4 as 1 and 3.5 as 4.
Number of Decodes
Number of decodes (ND) for a picket fence symbol is calculated by the following
formula:
Example:
1. The number 2 in the SPS formula ensures that each label receives two full raster sweeps.
Direction of label travel
Raster pattern
SwR
2 LS
×
SW LL
–
(
)
---------------------------
=
SW
5 inches
=
LS
2 inches per second
=
LL
1 inches
=
SwR
2
2
×
5 1
–
(
)
----------------
1
=
=
ND
LH DR
×
RH
SwR
×
--------------------------- 3
–
=
ND
1 900
×
10 1
×
------------------ 3
87 decodes
=
–
=