Opticon NFT 1125 - Manual (Page 15)

Manual No. 25-NFT1121-01
Series NFT-1121/2135 Mini CCD Fixed Position Scanners
2) Avoiding Specular Reflection
Do not position the scanner at an angle that causes the LED illumination to be reflected directly back into the
scanner. This is called specular reflection. Too much reflected light can “blind” the scanner preventing a good
decode.
If the bar code label is located on a flat surface, specular reflectivity occurs between 2 to 9 degrees off perpendicular
(see diagram). If the bar code label is located on a cylindrical surface, such as a test tube, the angle of specular
reflection is measured tangent to the curve. If the curved surface is also moving, there may be more than one
position causing specular reflection. The following diagram indicates the area to avoid:
3) Quality Bar Code Labels
The quality of the bar code label can affect the scanning performance. Poor quality labels are more difficult
to decode and may result in non-reads or potential misreads. The bar code label should be printed to
specifications. This means that the bars are printed within spec, with the correct widths, no ink spread, crisps
edges and no voids. There should be a sufficient quiet zone on both end of the bar code label.
For best results the paper or label stock should have a matte finish to diffuse light. The print contrast signal
(which is a comparison of the reflectance of the bars and the background stock) should be as high as
practical.
Page 9
LEDs
Ba
r
Co
de
Avoid 2-9
Bar Code
Avoid 2-9
L
E
D
s