Reliance 4: Using data structures in combination with OPC servers

2009 | Reliance SCADA

Most OPC servers enable you to browse OPC tags (items) and import them into a visualization project. Imported with each tag is all important information about it. Thus, importing OPC tags significantly eases the project development. However, if you have ever used data structures (user-defined structured data types) in a Reliance 4 project, it might have occurred to you that it would be great to be able to import even structured tags from an OPC server. Unfortunately, this is not possible since OPC servers only support the standard data types, such as Byte, Word, Integer and Float. Therefore, structured tags must be added to an OPC device individually (by using the "New Structured Tag" command in the Device Manager). Both the approaches can be combined, though. This means that you can import tags of simple data types and manually add structured tags. It saves a lot of development time even on projects with a few structured tags since each structured tag can contain tens of nested tags (data structure fields can, in turn, be data structures).

Previously, the most tedious part of the work when using data structures in combination with an OPC server was entering the value of the "OPC ItemID" property for the tags nested in structured tags. This drawback was solved in Reliance 4.0.18 by adding the "Automatically generate OPC ItemID for nested tags" property for devices of type OPC. This property substantially facilitates defining structured tags. You just specify "OPC ItemID" for structured tags and for all the nested tags, "OPC ItemID" is generated automatically based on their names. The only condition for this to work properly is that data structure fields (defined through the Data Structure Manager) must have the same names as in the OPC server configuration.

Data Structure Manager – a data structure named "Cabin" for devices of type OPC

Device Manager – a device of type OPC with the "Automatically generate OPC ItemID for nested tags" option active

Device Manager – a structured tag named "PLC.CPU.DB.Cabin3" of type "Cabin" with the "OPC ItemID" property value manually entered

Device Manager – a nested tag named "Contactor_Time" with the "OPC ItemID" property value automatically generated