Formulas for Number of Decodes
MS-850 Raster Scanner User’s Manual
A-11
Appe
ndices
Appendix E — Formulas for Number of Decodes
To ensure reliable scanning, apply a minimum of
five
decodes to each symbol. Use the
formulas below to calculate the number of decodes that your label will receive.
If the number of decodes you derive from one of these calculations is less than the
minimum for your application, plug in the minimum number of decodes (5) and solve
for another parameter that might be changed, such as label speed or scans per sec-
ond.
Single Line Ladder Calculation
Ladder scanning is seldom done with raster scanning
unless the raster is set for single scan line scanning (
Top
Offset
setting equal to
Bottom Offset
) or symbols are
presented as stop-and-go.
For single scan line ladder scanning, use the following for-
mula:
1
LH
(Label Height) (ladder formula only) is a measurement of the height of individual bars.
LS
(Label Speed) is the distance per second that a symbol moves through the scan.
DR
(Decode Rate) is the number of decodes per second that a given symbol receives
(as derived from a stationary scan test).
Example:
1. The -3 component in the formula is included to allow for AGC acquisition, an incomplete first
scan, and an incomplete last scan. This applies only if the number inside the parentheses equals
4 or more. If the number equals 3, then only subtract 2 to derive 1 good scan.
Direction of label travel
Scan Line
LH
LS
-------- DR
×
3
–
ND (number of decodes)
=
LH
1 inch
=
LS
100 inches per second
=
DR
900 scans per second
=
ND
1
100
--------- 900
×
=
3
–
6 complete decodes
=