Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 32)

Chapter 4
Configuring Your Decoder
4–5
(Continued)
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2) Display Status and Counters - After selecting this operation by pressing
the [2] key at the select operations menu, the decoder will display the
following:
•
Decoder Performance - The percentage of decodable scans over a 100
scan sample. The 100 scan sample is not made up of the raw scans from
the scan head. Instead, the 100 scan sample is made up of scans which
have passed through a “qualifier” circuit in the data acquisition circuitry.
The “qualifier” circuit acts as a pre-filter that discards empty, partial, or
noisy scans before decoding is attempted. Because of this, it is possible
to have a high decoder performance even though only a small percentage
of the scans are crossing the label (such as when a raster scan head is used
or the label is moving). This display is only available if continuous
trigger mode is selected and fields per package parameter (entered as part
of configuration programming) is anything but “any”.
Note: You can use the decoder performance monitor during:
Installation. By monitoring the percentage of good reads, you will be able to
determine the optimum location for the scan head in relation to the label(s)
being read.
Operation. If the percentage of good reads drops significantly below what it
was during installation, the scan head window may require cleaning or the
label quality may have degraded.
•
No-Read Counter - The number of No-Reads. This counter is
incremented each time a package start trigger is generated and a stop
trigger occurs without a valid package. No-reads also occur when the
decoder does not decode the correct number of fields on a package as