Opticon NFT 2100 manual Achieving Optimum Performance, Distance to the Bar Code and Depth of field

Manual No. 25-ULNFT2100-01; Mar, 2005	NFT 2100 CCD Fixed Mount Barcode
Scanner
Section 3
Positioning the Scanner for Optimum Performance

Achieving Optimum Performance

Four items greatly impact performance:

1)Distance (from the scan window) to the bar code

2)Field of View

3)Specular Reflection

4)Quality of Bar Code Labels

1)Distance to the Bar Code and 'Depth of field'

The ideal location of the bar code relative to the scanner is at its focal distance, about 1.4" from the front of the unit. A bar code located either too near or too far from the scanner will be out of focus for the scanner camera causing the scanner to have difficulty decoding what appears to be fuzzy bars and spaces.

Just as with any camera, the scanner has a working depth-of-field (DOF). It can read bar codes that are not precisely at its focal distance - maybe a little closer, or a little farther away. The DOF varies based on the density of the bar code, i.e., the thicker the bars and spaces the more DOF. Very high density bar codes (which have very narrow bars) are readable over a much shorter DOF 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 NFT 2100 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.

Depth-of Field NFT 2100 (Specification)*

Density	Min. Distance	Max Distance	Range
	(inches)	(inches)	(inches)
6 mil	0.9	1.6	0.7
10 mil	0.8	1.7	0.9
20 mil	0.8	2.0	1.2
40 mil	0.9	2.4	1.5

*measured from front edge of scanner

2)Reading width or Field of View of the scanner

The table below shows the field-of-view (FOV) at various distances from the window. The FOV is the maximum width that the scanner is capable of reading. It is the distance from the left edge of the view to the right edge. For the NFT 2100, the FOV will be 3.1" at its focal distance of 1.4". Any part of a bar code label that is positioned outside of the FOV will make the label unreadable. Good design policy is to position the barcode at the center of the FOV where the camera sees best.

Remember: The width of a bar code label includes not only the bars and spaces but also the required white space (quiet zone) on each end.

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