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206 Siemens Simatic S7 Driver Online Help

You may be able to prevent overruns by phasing datablocks. Refer to Using Phasing

with Poll Rates for details on phasing datablocks.

You can set the poll rate to zero or to a subsecond value from 0.1 and 0.9. For

example, you could set the poll rate to 0.5. Setting the poll rate to zero or a subsecond

value disables overruns. Entering a zero poll rate also forces the driver to run at its

maximum rate. In general, you should set the poll rate to less than 1, if it is more

important to run the driver at a fast speed than to detect overruns. If you plan to use a

poll rate less than 1, make sure your process hardware supports subsecond values.

Understanding Data Quality

The SI7 driver displays the quality of the data in the selected datablock as part of its

statistics. Data quality can be good, bad, or uncertain. Each quality type can also

have the following additional text (substring) to further explain the quality:

The OPC Foundation defines each quality type and substring. For more information

on the definition of each item, visit the OPC Foundation’s web site at

www.opcfoundation.org.

The data quality... Can include the text...

Good Local Override

Bad • Config Error

• Input not Connected

• Device Failure

• Sensor Failure

• Data Latched

• Communication Failure

•Out of Service

Uncertain • Last Usable Value

• Sensor not Accurate

• EGU units exceeded

•Sub-normal

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Siemens SIMATIC NET Spezifikationen Seite 216