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Verification
Verification equipment is a necessary part of an accurate
system. These units, which come in both portable and on-line
models, check the quality of printed symbols by decoding
them and measuring their key characteristics. Your verifying
unit must be able to identify any variations that are too
great to allow accurate scanning and reading.
Verification Guidelines
Two closely related tests of bar code quality are the
First-Read Rate (FRR) and the Substitution Error Rate (SER).
The FRR is the percentage of times your codes can be
successfully scanned on the first try. A success rate of at
least 85% should be the norm, which much higher rates
possible. The SER is the rate at which a character in a code
is improperly substituted for another. As a general rule,
the SER should not exceed one error per one million
characters.
To meet these tests, your equipment should test your
codes against a number of industry and ANSI verification
standards for each symbology and for bar codes overall.
Among many other requirements, these standards cover:
Printing tolerances for bar and space dimensions.
Optical properties such as reflecting light at an
adequate intensity.
Print quality problems such as imperfections or
ragged edges in bars or spaces.
Types of verification equipment include the following:
Portable units are often hand-held non-contact
scanner-type pens or wands equipped with lasers. They
serve well for verifying symbols during printing or for
symbols attached to rough, curved, and other irregular
surfaces.
On-line units are mounted on or within a printer
and automatically examine symbols during printing. A
good verifier will stop the printer operation or set off
an alarm if a bar code is defective or unscannable.
Bar Code Reading
Bar code reading involves two main functions: scanning
and decoding. Scanners use visible or infrared light,
created by lasers and other technology, to register
character widths and patterns. Decoders transmit the data to
a PC, controller, or host computer system. Portable,
stationary, and combination decoders are available, and may
be part of or connected to the scanning unit. In the
description below, scanners and decoders are considered as
units.
Two key criteria for bar code reading equipment include:
Autodistinguishing: Your scanner should be able
to recognize a number of selected symbologies and
process their data.
Autodiscrimination: Your decoder should also be
able to recognize and correctly translate data from
selected symbologies.
Contact Scanner/Decoders
Contact scanner must either touch or come close to the
symbol, and are usually hand-held units. They are designed
for situations where the scanner must be taken to the item,
or where the label cannot be easily read from a distance.
Retail clothing tags are an example.
The most common type of contact scanner is a pen or wand.
Keep the following in mind when selecting and using these
devices:
Match the wand resolution to the code density. A
high-resolution wand works best with high-density
symbols and vice-versa.
Label stock must be sturdy enough to withstand
repeated contact.
Operators should be instructed to hold the
scanner at the correct angle to the symbol (usually 45
to 90 degrees), move the scanner across the symbol at
the correct speed (usually 3-6 inches per second), and
scan the entire symbol from quiet zone to quiet zone but
not beyond.
Non-Contact Scanner/Decoders
Non-contact scanner do not have to contact the symbol,
and include both hand-held and stationary units. Some units
can read large symbols at a distance of several feet.
Non-Contact Scanner Light Beams
These scanners use either moving beams or stationary
beams. Stationary beams must be moved across the symbol by
moving either the scanner or the item. A moving-beam scanner
contains an oscillating light that is aimed at the symbol
and turned on.
Hand-Held vs. Stationary Non-Contact Scanners
Except for not requiring contact with the object scanned,
hand-held non-contact scanners function similarly to
hand-held contact scanners. Fixed-beam hand-held scanners
serve well at scanning soft or irregular objects and objects
at a distance. Moving-beam hand-held scanners require fewer
operator skills. The moving beam automatically oscillates to
scan the object rapidly and repeatedly.
Stationary scanners are usually mounted in a permanent
location, frequently near conveyors. A fixed-beam stationary
scanner requires good print quality to read correctly on the
first read. A sample application is a table-top scanner at a
grocery store checkout station. Price labels are read as the
item is moved across the scanner.
Moving-beam stationary scanners are effective in highly
automated applications. Oscillating beam scanners are able
to achieve high rates of scans per second. The item, carton,
or pallet to be scanned may be moved past the scanner
without direct human involvement at speeds over 1,000 feet
per minute.
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