Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 58)

Chapter 4
Configuring Your Decoder
4–31
CAPTURE COUNT (o) - The capture count field sets the number of
identical and valid scans that must be decoded before the read is considered
valid. This entry is a numeric value from 1 through 8. The default value is 2.
When a poor quality label is scanned, it is possible for the decoder to
interpret the label in one of three ways:
•
Valid Scan. The decoded information matches label.
•
Undecodable Scan. The video data sent from the scanner to the decoder
does not correspond (for any or all characters) to a valid pattern within the
symbology selected.
•
Mis-Read. Or substitution error; the video data for a particular scan
matches a valid pattern within a selected symbology that is different from
the intended pattern. This error is often caused by smudges, stray marks,
voids, or print errors that result in wider or narrower bars being decoded.
The purpose of the capture count is to reduce the chance of a mis-read by
forcing the decoder to read the label multiple times before issuing a valid
read.
Certain bar code symbologies are more susceptible to mis-reads because they
are not self checking (Code 39, Interleaved 2 of 5, and Codabar when check
characters are not used). For these bar code symbologies, the capture count
should be set to no less than two.
Setting the capture count too high may result in excessive “no-reads“,
particularly when the number of scans crossing the label within a trigger
period is low (5-10 scans). The capture count should be set to a value which
results in minimum mis-reads and maximum valid reads. We recommend
that the capture count should be set no greater than half of the number of
scans crossing the label in a trigger period. The capture count should be set
to at least two for symbologies that are not self checking.
FIELDS/SCAN (p) - The fields per scan field sets the number of bar code
labels that are to be included in each scan. The bar code fields in each scan
must be of the same symbology type. A scan refers to the movement of the
laser beam from one side to the other. During the scan, the decoder looks for
a valid bar code field to decode. On a single scan, the decoder can decode up
to 4 successive bar code fields. You can select from five options: 1, 2, 3, 4,
or Any. If you select ANY, the decoder will look for 1, 2, 3, or 4 fields. For
optimum performance and security against missing labels, we recommend
that you specify the number of fields per scan.
Note: If the decoder is operating in any of the triggered modes and you select
“ANY” fields per scan, multiple bar code fields in each label should have
unique first characters. If two bar code fields have the same first characters,
the decoder will assume duplicate fields have been decoded and ignore the
second field.
FIELDS/PACKAGE (q) - The fields per package field sets the number of
bar code symbols that are on each package being scanned. You can enter a