Siemens SIMATIC MV500, Operating Instructions Manual, Page: 51 / 294

Image processing
3.2 Code verification
SIMATIC MV500
Operating Instructions, 03/2021, C79000-G8976-C494-05
51
Procedure
To calibrate the optical reader, follow these steps:
1.
Make sure that you have stable and uniform illumination of the working area of the optical
reader in particular the surrounding lighting.
For this purpose, read the information in the section introduction.
2. Place the calibration plate in the viewing range of the optical reader.
3. From the codes available on the calibration plate, select the one whose cell size comes
closest to the codes to be verified.
4. Position the selected data matrix code (the version with approximately 80% contrast) in the
center below the optical reader.
5. Align the borders of the code parallel to the borders of the image.
The centering aid drawn into the image serves as an aid.
If, during processing, the code to be read is always positioned in a region below the
optical reader that is clearly offset from the center, you should also position the
calibration code in this region.
6. Check the image of the code and optimize the image quality.
As an aid, you can enable the sharpness display in the "Image view" group.
Using a small aperture achieves a greater depth of focus. A small aperture is also advisable
if the optical reader cannot be protected from surrounding light. A large aperture,
however, allows shorter exposure times and is therefore useful for fast applications and
for verification according to ISO/IEC 29158.
7. When there are other data matrix codes in the image field or the illumination is not uniform
across the entire image surface or the code is not located in the center of the image due to
the application, the calibration ROI will need to be adapted.
To this end, adjust the ROI so that the code is located in the center. The exact size of the
ROI is unimportant but must contain the complete code and the quiet zone (minimum
width: 1 code cell).
8. If required to meet the requirements of your application, configure the maximum exposure
time and brightness.
To achieve a good image quality, the maximum brightness for the verification is more
restricted than when using the device as an optical reader.
– To minimize any possible deterioration of the measured code quality due to the image
acquisition procedure, the brightness is set to as low a value as possible during
calibration. The required exposure time is therefore relatively high in many cases. For
applications with direct part marking (DPM) a lower calibrated exposure time should be
selected under certain circumstances. This applies in particular if active exposure
control is used with ISO/IEC 29158. The exposure time can then be corrected during
processing mode to be able to verify parts with weak reflectance.
– To achieve a shorter exposure time, set a lower value for the maximum exposure time.
The maximum exposure time allowed in processing mode can be adapted in the
program settings (only ISO/IEC 29158).