Siemens SIMATIC MV500, Operating Instructions Manual

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Image processing
3.2 Code verification
SIMATIC MV500
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Operating Instructions, 03/2021, C79000-G8976-C494-05
3.2.5.3 ISO/IEC 29158
This standard is based on ISO/IEC 15415 but includes modifications for more robust
measurements of Direct Part Marks. The standard can be used for a wide range of
applications, sectors and marking technologies.
The most noticeable differences are the use of automatic exposure control and a much
greater contrast tolerance.
Note
ISO/IEC 29158 uses its own algorithm for exposure control
The ISO/IEC 29158 standard uses its own algorithm for exposure control. With this, the
exposure time is adjusted so that the average gray scale value of the code to be verified is
between 70% and 86%. If such an exposure is not possible for a particular code, a verification
error (4707, 4708, or 4709) is generated.
Automatic exposure control requires multiple decodings of the code to be verified. The time
needed for this can vary significantly depending on the type and marking quality of the code.
The "Time limit" parameter in the exposure settings of a program can be used to limit the
time available for exposure. Occurrence of the verification error 4709 and, in particular, 4708
indicates that the value is too low.
Checking of the average gray scale value can be disabled by clearing the "From reference"
check box in the exposure settings of a program (not recommended). The verification no
longer conforms to the standards in this case.
Note
Uncalibrated verification or verification not conforming to standards according to
ISO/IEC 29158
Because the "Cell contrast" quality parameter in ISO/IEC 29158 is calculated depending on the
average gray value:
If the average gray value fluctuates from one image acquisition to another, the calculated
value is not informative. See also the note above on exposure control.
Therefore, when ISO/IEC 29158 is used for uncalibrated verification, the "Cell contrast" quality
parameter is not used by default for determining the overall quality. A poor grade for cell
contrast thus does not affect the overall grade. The same applies if the "From reference"
check box is cleared for calibrated verification. If the "Cell contrast" quality parameter is to be
used for the overall quality, select the "Evaluating symbol contrast" check box in the
"Advanced" tab of decoder steps.
Note
Verification report
You can create a verification report according to ISO/IEC 29158 using the WBM. For detailed
information refer to the online help of the WBM.