Cognex DataMan 475, Reference Manual, Page: 39 / 55

Grading Standards and their Parameters
ISO/IEC 15415 Grading Parameters
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UEC (Unused Error Correction) is the percentage of error correction capability that is available for further
incorrect modules. The assignment of grade is according to the following table:
UEC % Grade
> 62 A (4.0)
> 50 (but less than 62) B (3.0)
> 37 (but less than 50) C (2.0)
> 25 (but less than 37) D (1.0)
< 25 F (0)
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SC (Symbol Contrast) is the difference in reflectivity between the brightest module and the darkest module. The
assignment of grade is according to the following table:
SC% Grade
> 70 A (4.0)
> 55 (but less than 70) B (3.0)
> 40 (but less than 55) C (2.0)
> 20 (but less than 40) D (1.0)
< 20 F (0)
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MOD and RM (Modulation) is a grade based on the amount of variability in reflectivity of the modules. A multi-
step process is used to get the modulation grade. First, the reflectivity of each module is compared to the global
threshold and the overall symbol contrast according to the following formula:
MOD = 2 * (abs(R - GT)) / SC
The Global Threshold GT is the midpoint between the reflectance of the brightest module and the reflectance of the
darkest module. Next, the grade level for each module is determined from the MOD value according to the following
table:
MOD % Grade
> 50 A (4.0)
> 40 (but less than 50) B (3.0)
> 30 (but less than 40) C (2.0)
> 20 (but less than 30) D (1.0)
< 20 F (0)
The value of the grade for the Modulation parameter is the highest modulation level for which the modules meeting that
level result in a notional Unused Error Correction grade of that level or higher. The module with the lowest MOD is
reported as Contrast Uniformity (CU) in General Characteristics to facilitate conformance testing to the requirements of
ISO/IEC 15426-2.
The RM parameter works in a similar way, except that for modules which error correction corrects as errors, the MOD% is
taken as 0 and counts as F in the final evaluation of the Modulation parameter grade according to the notional Unused
Error Correction grade.
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Grading Standards and their Parameters