Welch Allyn Scanteam 6180, Техническое руководство

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2–2
Operational Description
2.3 Operating Theory
The reading ability of the wand scanner is based on the detection of
reflected illumination from the bars and spaces which form a bar code
symbol.
During a typical scanning operation, the tip of the scanner is moved across
the bar code symbol. Illumination from the LED is focused on the bar
code symbol. This is absorbed by the dark colored bars and reflected by
the lighter background.
The reflected portion re–enters the scanner through the lens where it is
detected by the read sensor photodiode. The photodiode converts this into
a series of analog pulses which are proportional in width to the bars and
spaces in the symbol. These pulses are then digitized and sent to the
microprocessor where they are decoded into the characters represented by
the bar code symbol.
2.4 Factors Affecting Scanning Performance
The following factors influence reading performance and should be
considered when selecting a contact scanner for a particular bar code
application.
2.4.1 Scanner Illumination Source
Wand type scanners are equipped with a visible red (660nm) source. Red
illumination is compatible with most printing inks including most thermal
papers. Because it provides a visual indication to the operator that the
scanner is functioning, red illumination is considered to be more user
friendly. Visual feedback to the operator is an important consideration
when making a scanner selection.
2.4.2 Scanning Aperture
Scanning performance is affected by the size of the scanning aperture and
it is a significant factor to be considered when selecting a scanner. The
scanning aperture defines the effective size of the area of the bar code
symbol viewed by the scanner optics. It affects the relative ability of the
scanning device to “see” or resolve bars and ignore printing defects.