Appendices
MS-860 Industrial Raster Reader User’s Manual
A-21
Raster Picket Fence Calculation
For raster picket fence scanning, the number of
decodes (ND) that can be applied to a given symbol
can be calculated once the sweep rate (SR) is known.
Sweep Rate
(SR)
Sweep rate is the number of raster sweeps (up or
down) that occur per second and can be set in
ESP.
Since the sweep rate cannot exceed 30 you first need
to ensure that your application can achieve this by
solving for sweep rate. The sweep rate should gener-
ally be set as low as possible in order to maximize the
number of scans on a given symbol.
The formula for determining
Sweep Rate (SR) is as
follows:
1
SR = Sweep Rate, the number of passes, up or down, that are described by the arc of
the raster mirror.
SS = Scan Speed, the distance per second that a symbol moves through the scan.
SW = Scan Width, the width across the scan beam, at a given distance from the
reader, in which a symbol can be read (picket fence formula only).
SL = Symbol Length, the length of the longest printed symbol to be read plus the
length of the quiet zones (picket fence formula only).
Example:
Important: The maximum sweep rate that your can set the reader to is 80. If your
solution is greater than 80, you must change another parameter such as scan speed,
etc. and recalculate.
Since SR can only be entered into the software as whole numbers, round off fractions of
SR to the next higher number, for example enter 0.4 as 1 and 3.5 as 4.
In setting up the reader, raster height depends on the raster arc and the symbol dis-
tance (range) from the reader. Both the top offset and bottom offsets can be adjusted
independently in 255 increments and the resulting arc can vary from 0° to 30°. (See
Chapter 8,
"Raster/Laser"
.)
1. The number 2 in the SR formula ensures that each symbol receives two full raster sweeps.
Direction of symbol travel
Raster pattern
Raster
Picket Fence
SR
2
SS
×
SW
SL
–
(
)
---------------------------
=
SW
5
=
SS
2 inches per second
=
SL
1
=
SR
2
2
×
5
1
–
(
)
----------------
1
=
=
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