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TN Hist307 Understanding OPC Quality 252




This article from InSource details OPC Quality 252

  • Author: Peter Farrell
  • Published: 9/19/2019
  • Applies to: Historian all versions


When good values ae stored in Historian, each good value is usually flagged as good by an OPC value of 192. Occasionally you may notice OPC values of 252. This is usually not an issue, but if you see repeated values for which the OPC Quality is 252 and periods where NULLs show up, you may have a slow changing tag value.

OPC Quality 252 is reporting that the value is the first value received from the IO Server. OPC Quality 252 is actually reporting good quality data, but it’s also indicating that the value for which quality 252 is reported is the first good value received from the IO source. One important consideration to note about Quality Detail 252 is that timestamp is not necessarily when the value actually changed within the PLC/device since the tag value most likely changed prior to the reconnect event.

You might see OPC Quality 252 under one of the following scenarios:

1. The value is the first received after an orderly startup of the IO source. If this is the case, no intervention is necessary. Subsequent values for the same tag should be stored with an OPC Quality 192.

2. The IO Source is dropping out and in. For some reason, the IO server is stopping or failing and restarting. The Wonderware Logger may contain various messages, warnings, and errors which may indicate the source of the problem.

3. The IO value is slow changing and as a result, the topic within Historian is timing out. Periodically the system will retry to read a value from the topic and the next time a change in value is detected and flagged as good, it will be written to the Runtime database with an OPC Quality of 252. If the value is inherently slow changing you can set the Historian Topic properties to “Set to No Timeout”. The Wonderware Historian help files include the following detail about this setting.

To disable the time out, select Set to No Time Out.
You might want to disable the time out if the topic has data values that are not changing at all or changing very slowly. If you have a slow-changing tag for which a time out is occurring frequently, you will see periods of NULL data in history, as a result of the historian disconnecting and reconnecting. Disabling the time out prevents the historian from disconnecting, so that valid data is always being logged.

To configure the topic for set to no timeout, open the Wonderware System Management Console (SMC)

Navigate to Historian > Historian Group > [your server name] > Configuration Editor > System Configuration > Data Acquisition > [your IDAS name] > [your topic name]
Right click on the topic and select Properties


The Topic DataSource Properties pane will open on the General tab.

Click the checkbox for Set to No Timeout


You will be presented with a popup warning. Click OK


Close the Topic DataSource Properties pane and right click the topic in the tree view (you should be able to right click on any leaf in the view to achieve the same outcome). Click the option to Commit Pending Changes from the popup pane.


The Commit Pending Changes Confirmation window will display. Click the Display button to display a list of changes pending to confirm that your change is ready to be committed.


The Pending Changes pane will display. The You may see changes other than the change that you just made to the topic. Confirm that any other changes displayed are currently permissible. If you are satisfied that your change is queued up as expected and other changes (if displayed) are permissible, click OK.


You will be returned to the Commit Pending Changes window. Click Commit.


Your topic is now set to no timeout and you should not receive further recurring instances of OPC Quality 252 for the topic modified where values are slow changing.