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Section 3 - Positioning the Scanner
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 0 to 10 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:
Height
of barcode
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, crisp
edges and no voids. There should be a sufficient quiet zone on both ends 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.
Measuring Scanner Performance
Two methods are helpful in determining the optimum position of the scanner. The first method is to program the
scanner for Trigger Disable and Continuous Read modes. The scanner will always be on and will
continuously read the same bar code. Since the buzzer sounds each time the bar code is read, the sound of
the buzzer can be used like a "Geiger counter." As the position of the scanner changes the sound of the buzzer
will change. The buzzer sound will be loudest and most continuous at the best reading positions.
Front View
Hatched no
read specular
˚
zone ±10
V520-LHA7127
11
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