Opticon LPN5627, LPR5627 user manual Distance to the Bar Code, Focal Distance, Depth-of-Field

Manual No. 25-ULPNR101-03; Feb, 2003	LPN5627 / LPR5627 Laser Fixed Mount
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)*

		Near	Far
Bar Code Density		Distance	Distance
40 mil	(1.00 mm)	2.3”	12.6”
20 mil	(0.50 mm)	2.3”	10.8”
10 mil	(0.25 mm)	2.3”	7.0”
6 mil	(0.15 mm)	3.5”	4.7”

* measured from front edge of scanner

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