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Manual No. 25-ULPNR101-03; Feb, 2003
Scanner
Section 3
Positioning the Scanner
Achieving Optimum Performance
Three items greatly impact performance:
1) Distance (from the scan window) to the bar code
2) Specular Reflection
3) Quality of Bar Code Labels
1) Distance to the Bar Code
The operation of the scanner is similar to a camera. If you photograph an object that is out of focus, the
resulting picture will be blurry. The same is true with the scanner. If the bar code label is out of focus,
the scanner may have difficulty decoding what appears to be fuzzy bars and spaces.
Focal Distance
Ideally, the distance from the window of the scanner to the bar code label should be equal to the focal
distance of the scanner. For the LPN5627 / LPR5627 fixed position scanners, the nominal focal distance
is approximately 4.0" from the front edge of the scanner
Depth-of-Field
Just as with a camera, the scanner has a depth-of-field. It can read bar codes that are not precisely at
the focal distance - maybe a little closer, or a little farther away. However, if the bar code label is
positioned too far from the focal distance, the scanner may not be able to successfully decode it.
The depth-of-field varies based on the density of the bar code, i.e., the thickness of the bars. Very high
density bar codes (which have very narrow bars) are readable over a much shorter distance range than
low density bar codes with larger bars.
The following table shows the depth-of-field specifications (closest to farthest reading distances) for the
LPN5627 / LPR5627 scanners. The actual performance may differ slightly from unit to unit. Also, it is
important to note that this data was measured under ideal conditions using high quality bar code labels.
In a "real world" environment the conditions will not be as ideal. Therefore, the best practice is to
position the scanner at the center of the depth-of-field rather than at the extremes of its depth-of-field.
Depth-of Field LPN5627 (Specification)*
40 mil (1.00 mm)
20 mil (0.50 mm)
10 mil (0.25 mm)
6 mil (0.15 mm)
* measured from front edge of scanner
Bar Code Density
LPN5627 / LPR5627 Laser Fixed Mount
Near
Far
Distance
Distance
2.3"
12.6"
2.3"
10.8"
2.3"
7.0"
3.5"
4.7"
Page 7
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