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Manual No. 25-ULPNR102-01; Mar, 2005
Section 3
Positioning the Scanner for Optimum Performance
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 ideal location of the bar code relative to the scanner is in the waist of the laser beam. A bar code
located either too near or too far from the scanner relative to the waist may cause the scanner to have
difficulty decoding what appears to be fuzzy bars and spaces. For the LMD 1135 fixed position scanner,
the waist is approximately 2.5" 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 laser beam waist - maybe a little closer, or a little farther away. However, if the bar code label is
positioned too far from the waist of the beam, 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
LMD 1135 scanner. 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. Data taken
for a "typical" unit randomly drawn from stock is presented in Appendix E.
Depth-of Field LMD 1135 (Specification)*
40 mil (1.00 mm)
20 mil (0.50 mm)
10 mil (0.25 mm)
6 mil (0.15 mm)
5 mil (0.127 mm)
* measured from front edge of scanner
Bar Code Density
LMD 1135 Laser Fixed Mount Scanner
Near
Far
Distance
Distance
4.3"
14.2"
3.1"
9.8"
2.4"
5.7"
1.8"
3.1"
2.2"
2.8"
Page 8
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