Barcode verification

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Interpretation of results - Linear barcode verification

Reflectance margin

This is the value of the least reflectance difference of a bar of space from the global threshold. If this value is less than 5%, when measured as a percentage of the symbol contrast, there is a possibility that the symbol is close to failing because the edges of the bars and spaces cannot be determined. If it fails, the symbol will score 0.0 or F for decode.

 

Calculating the final grade

The lowest grade (of the seven different parameters) from each scan is averaged to produce the overall grade.  As the scans are taken at different heights through the barcode the final grade will give a good indication of whether a barcode will or will not scan.

 

Aperture

Finally there is an important factor to consider concerning the reading head. In most scanning situations an appropriate scanner will have been selected for the size of bars and spaces in the code, and the ISO/IEC method takes this into account. For instances where very narrow bars and spaces exist in the barcode, a special high resolution scanner will be needed, and it makes sense to verify the code with this in mind. Conversely when a barcode is going to be used that has very wide bars and spaces, a much lower resolution scanner can be used, ensuring that fine details, such as very small holes or extra specks of ink, do not affect the results unnecessarily.

 

This situation is exactly what we see when codes are printed on fibreboard outer cases. Here ink coverage is often not perfect, and holes or ink spots may exist that do not affect the scanning because a low resolution scanner is used.

ISO/IEC Grade ANSI Grade
3.5 to 4.0 A
2.5 to 3.5
B
1.5 to 2.5 C
0.5 to 1.5 D
0.0 to 0.5 F
Symbol contrast percentage value ISO/IEC grade
≥ 70% 4.0
55% to 69%
3.0 to 3.9
39% to 54% 2.0 to 2.9
20% to 38% 1.0 to 1.9
15% to 19% 0.1 to 0.9
<15% 0.0
Modulation percentage value ISO/IEC grade
≥ 70% 4.0
60% to 69%
3.0 to 3.9
50% to 59% 2.0 to 2.9
≥40% to 49% 1.0 to 1.9
30% to 39% 0.1 to 0.9
<30% 0.0
Defects percentage value ISO/IEC grade
≤ 15% 4.0
16% to 20%
3.0 to 3.9
21% to 25% 2.0 to 2.9
26% to 30% 1.0 to 1.9
26% to 30% N/A
>30% 30%
Decodability percentage value ISO/IEC grade
≥ 62 % 4.0
50% to 61%
3.0 to 3.9
37% to 49% 2.0 to 2.9
25% to 36% 1.0 to 1.9
20% to 24% 0.1 to 0.9
<20% 0.0

The ISO/IEC standards specify that the size of a verifier's measuring aperture should be chosen to match the size of the bars in the printed code.

 

Aperture sizes are often quoted in units of 1/1000 of an inch. This unit is sometimes referred to as a ‘mil’. Note that this is not the same as a millimetre.

 

The grade for a barcode should ideally state the aperture used for the verification and the wavelength of light being used by the verifier, like this 3.7/06/600, where 3.7 (A) is the measured grade, 06 the aperture reference number, and 660 the wavelength in nanometers.  The aperture reference number is equal to the diameter of the aperture measured in mils.

 

The Axicon 6015 will choose the correct aperture for most applications automatically, but the user can choose whether the EAN/UPC barcode will be scanned only at the retail point of sale, or in general distribution. If the verifier cannot use the correct recommended aperture it will select the closest available, and the Summary window will show a warning, along with both the used and recommended apertures.

 

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Axicon Auto ID is a world leader in barcode verification, having developed and manufactured our own range of verifiers since 1989. Axicon barcode verifiers are used to measure the quality of linear and matrix barcodes, on all levels of product packaging.

 

 

 

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