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» CCD Scanners
Of the two "non-contact" technologies (CCD and laser),
CCD scanners are generally the lower cost.
CCDs use similar technology to that used in modern video cameras;
they "scan" the bar code by registering a complete image
of the code at once. CCD scanners are usually characterised by their
wide heads and the way that they appear to illuminate the bar code
in (usually red) light. You have probably seen these scanners used
at check-outs in places such as DIY stores.
Although technically a non-contact technology, most CCD scanners
have a depth of field, i.e. reading distance, of only one or two
centimetres. Recent advances in optics though are now enabling some
CCDs to work at longer distances, in some cases five centimetres
or more. Generally, CCD scanning remains a close proximity reading
CCD scanners can come with a variety of output and interface types
depending on the individual model and manufacturer. Because CCD
scanners already contain a built in microprocessor, the output is
usually in a format that has already been decoded. Common output
types are RS232 serial, TTL serial or keyboard wedge interface.
Apart from the need for close proximity, the only real drawback
to CCD scanners is the need to match the maximum reading width of
the scanner head to the bar codes to be read. Hence a CCD scanner
with a maximum head and reading width of 60mm cannot read a bar
code that is 70mm wide. Generally the widest head width for regular
style CCD scanners is around 80mm.
It would seem logical therefore to always select the maximum head
width scanner available. However, there is sometimes a very marginal
trade off between greater width of CCD head and first time read
rate, narrower heads sometimes having a slight performance advantage.
Hence care should be taken in selecting a CCD scanner with the optimum
head width. For much larger bar codes it is usually necessary to
go up to laser scanners. One further limitation concerns curved
surfaces: while CCD scanners can cope with modest curvature much
better than a wand can, CCD readers are not usually designed to
cope with the optical effects of curvature.
CCD Scanners probably represent the best value for money option
for close proximity scanners and a good number are sold as wand
upgrades. If getting close to the code is not a problem and the
throughput requirement is medium volume, then CCD scanners are a