OPC > OPC Interface Service > Writing to an OPC Server

Writing to an OPC Server

To write to an OPC server connected to an OPCIS, you edit the value of the tag in the OPCIS. This is different from other current value services. With other current value services — in particular the UIS — if you edit a value the change resides only in CygNet. It is not propagated down to the device. In an OPCIS, the changed value is sent to the OPC server.

To Write to an OPC Server

  1. Using CygNet Explorer, click on the OPCIS in the service hierarchy.
  2. Right-click on the tag for which you want to change the value and select Properties.
  3. Click Edit Value.
  4. Type the new value and click OK. The changed value will be sent to the OPC server.

Note: When updating point values (via a value edit in CygNet Explorer, using the TextImport EIE, or via a SetPoint object) all changes are pushed through to the associated CVS (UIS, HSS, and OPCIS). In the case of the OPCIS, you cannot do a text import or a setpoint to an OPCIS point if an external OPC server ID is configured (in the External ID field of the Point reference page of the PNT Editor) because any update is routed back through the external OPC server. This makes it impossible to backfill historical data for a tag that "belongs" to an OPC server.

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