Topics

Add Topics

To add topics, click the “Add” button with the OPC DA Server selected in the main application’s nagivation pane. A topic with a default name and settings will be created.

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Topic Settings

Click on a topic in the navigation panel to view topic settings.

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For each topic you can configure:

  • Name
    The topic’s name.
  • Access
    How the topic should be accessed, either “Read-Only”, “Read-Write”, or “Write-Only”. If Read-Only then Dataristix will allow use of the topic as task input only. If Write-Only then Dataristix will allow use of the topic as task output only. If Read-Write then the topic can be used in inputs as well as in outputs. Note that this access mode is not related to the underlying OPC DA Server tag access level; for example, a topic that is configured as writable (Read-Write or Write-Only) cannot write to OPC DA tags if the OPC DA Server does not allow writing to the tags.

For readable topics:

  • Read rate
    The requested refresh rate for tag data in units of “Read Rate Unit” (see below).
  • Read Rate Unit
    The unit for “Read rate”, either milliseconds, seconds, minutes or hours.
  • Read mode
    Either “Subscription” or “Poll”. In Subscription mode the data is acquired by subscribing to OPC server data change events for the specified read rate; this is the most efficient form of data acquisition. In Poll mode data is read directly from the OPC server at the specified read rate.

Subscription mode options:

  • Share subscription for the same read rate
    This options is enabled by default. When checked, then all topics with the same read rate use the same OPC DA server subscription, which lowers the number of messages exchanged with the OPC DA server. When unchecked, then the topic is placed into its own subscription.

Poll mode options:

  • Poll max age
    When data is read from the OPC DA server then the “Poll max age” determines how “fresh” the data should be. A max age of zero means that the OPC server needs to read the data from the device; a higher max age value allows the OPC server to possibly satisfy requests using cached values if the cached value is not older than max age.
  • Sync poll with real-time clock
    If the read rate unit is Minute or Hour then the option to synchronize data requests with the real-time clock is available. If the read rate unit is Minute then reads occur on full minutes and if the read rate unit is Hour then reads occur on full hours.

For writable topics the following options are available.

  • Write uncertain tag values
    By default, only values of ‘good’ status are written to the OPC DA server. For example, if the input and output connectors of a task are both OPC DA connectors and the input connector sends data with an ‘uncertain’ status then the value is not written to the output OPC DA connector. Tick this option to also write ‘uncertain’ values. Values with a ‘bad’ status are never written.

Monitor Topics

Enable “Live Values” in the main application’s “View” menu to monitor the topic’s tag values. Live values are acquired according to the topic settings, (i.e. update rate) and are unavailable for Write-Only topics.

Remove Topics

Remove topics by selecting the OPC DA Server in the navigation panel, then select one or more topics to remove in the content panel, and finally click on the “Remove” toolbar button to remove selected topics.

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Warning

Note that topics are also removed from any task using the topics.