Appendix I Formulas For Number Of Decodes; Figure A-2 Ladder; Figure A-3 Picket Fence - Microscan MS-3 User Manual

Formulas for Number of Decodes
Appendix I — 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 symbol will receive.
If the number of decodes you derive from one of these calculations is less than the min-
imum for your application, plug in the minimum number of decodes (5) and solve for
another parameter that might be changed, such as symbol speed or scans per second.
Note: While the formulas given here solve for the predicted number of decodes, you
may also use the formulas to solve for other parameters that might be changed, such
as symbol speed, symbol length, etc.
Single Line Ladder Calculation
For single scan line ladder scanning, use the following for-
mula:
SH
 
×
------- -
DR
 
SS
SH (Symbol Height) (ladder formula only) is a measurement of
the height of individual bars.
SS (Symbol 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 in
Rate" on page
Single Scan Line Picket Fence Calculation
For single scan line picket fence scanning
use the following for-
mula:
( )
SW SL –
 
×
-------------------------- -
DR –
 
SS
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.
A-18
MS-3 CCD Reader User's Manual
– 3 = ND (number of decodes)
A-43).
3 = number of complete decodes
Direction of label travel
1
Direction of label travel
Scan line

Figure A-3 Picket Fence

Scan Line

Figure A-2 Ladder

"Test Decode
Label
placement
area