Welch Allyn Scanteam 6180, Техническое руководство

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2–4
Operational Description
In normal use, the wand is seldom held perpendicular to the surface of the
bar code symbol. Rather, an operator tends to tilt the scanner. Useable
scan angle is a function of tip geometry and depth of field. If the depth of
field is too small, the scanner may fail to operate at extreme tilt angles
(>35
°
).
Figure 2.2 Range of Angle
2.4.4 Scanning Velocity
The wand will operate at scan velocities from 2 to 50 inches/second (5 to
127cm per second) when the minimum bar/space size exceeds 7 mils
(0.18mm).
2.4.5 High Density vs Low Density Bar Code Symbols
Bar code density is a measure of the number of characters in a linear
measure of bar code. The standard of measure is normally given in terms
of the “X” dimension, the width of the narrowest bar code element. As bar
code density increases, the width of the narrowest bar code element
decreases. The scanning aperture should always be smaller then the
narrowest element to assure optimum resolution and the generation of a
digital signal which accurately represents the bar code.
2.4.6 Print Contrast
Print contrast is a measure of the relative difference in brightness between
the bars and spaces of a symbol and is specified as the Minimum
Reflectivity Difference (MRD). The MRD is the difference between the
lowest minimum space reflectance value and the highest maximum bar
reflectance value as measured across the entire symbol.
MRD = Max (R
b
max) – Min (R
s
min)
where: R
s
min = Minimum Space Reflectance
R
b
max = Maximum Bar Reflectance
The scanner will operate with a MRD as low as 37.5% with the proper
aperture and appropriate symbol.