Omron V440-F User Manual page 207

8 Advanced Settings
8-6-2 Symbol Grading
Grading Overview
The symbol grading features presented here are not intended to be, and should not be confused with,
barcode verification. The individual parameter measurements in symbol grading are implemented in
accordance with verification standards. However, calibration and other methodologies needed for
compliant verification are not feasible in a reader configuration. Compliant verification is beyond the
scope of this help topic, but reviewing a few topics can help in understanding how to deploy the
features and functionality provided.
Verifiers are integrated systems designed to meet the rigorous demands of the verification
specifications. To provide compliant verification, verifier systems are designed with specific features
and functionality. In addition to specific requirements that are explicitly defined in the standards
themselves, verifiers also incorporate general design features to eliminate sources of variability that
can have adverse effects on the accuracy and repeatability of measurements. Readers are designed to
provide maximum product flexibility for integration into systems that require reading for traceability. Key
reader design specifications such as size, cost, read range, and read rate are a few factors that drive
fundamental differences between verifier and reader designs. Understanding these tradeoffs in design
can help users to optimize their reader systems to provide better accuracy and repeatability when
grading.
V440-F readers provide no calibration features. The image captured by the reader is processed as-is
and the intensity values of the image 0 – 255 are directly mapped to 0 – 100% reflectance grading
purposes. Additionally, grading requires applying a synthetic aperture. A verifier normally applies an
aperture using application standard requirements in combination with dimensional calibration. Without
calibration the aperture needs to be specified by the user as a percentage of the nominal symbol
dimension. Finally, some metrics in verification such as Minimum Reflectance in ISO 29158 are
calculated using data that can only be provided through a calibration process and have no means of
representation without such a process.
Setup Considerations
Key setup objectives when grading standard printed marks are listed below. Note that grading certain
DPM marks with ISO 29158, such as dot peen marks, may require different and/or axial lighting to get
an appropriate response from the symbol.
• Select an optical configuration and distance that will achieve minimum pixel-per-element require-
ments for the target symbol. Select an optical configuration and illumination setup that achieves
the requirements at a working distance greater than or equal to 6". Working distances shorter than
6" can be used, although this introduces optical distortions that may impact performance of certain
measurements.
• Image the symbol as close to perpendicular as achievable in the application. Off-axis imaging
introduces distortions that can be significant, even causing the symbol to fail to read during the
grading process, resulting in all F grades.
• Achieve and maintain the best possible focus on the symbol when grading. Small variations in
focus can have substantial impacts on grading.
• Provide even external illumination at or close to 45 degrees of incidence and disable the internal
illuminating LEDs.
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V440-F C-Mount Code Reader User Manual