Topics

Add Topics

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

Topic Settings

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

For each topic you can configure:

• Name

  The topic’s name.

• Access

  How the topic should be accessed, either “Read Only”, “Read and 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 and 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 and 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 Cache Max Age [ms]

  When data is read from the OPC DA server then this setting 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.

• Convert to target type before writing values

  Tick this option to convert incoming values to the OPC DA tag’s target data type before writing, rather than writing values as received.

• 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.

• Write tag status

  Tick this option to write the status of each incoming value to the OPC DA tag, where supported by the OPC DA server.

• Write tag timestamps

  Tick this option to write the timestamp of each incoming value to the OPC DA tag, where supported by the OPC DA server.

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.

Warning

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