OPC-UA client function blocks for IEC 61131-3

15 April 2014

Cooperation between PLCopen and OPC Foundation began in 2008 to map the IEC 61131-3 Software Model to the OPC UA information model, which was released in March 2010 by both organisations. 

In 2011 the working groups initiated the next step, adding the OPC UA client functionality in the controller by defining a set of Function Blocks for IEC 61131-3. This specification has just been released, making the controller an intelligent part in the IT communication. 

In terms of communication, this model represents the assumption that a controller, as a main component of the automation system, is ‘dumb’ towards the higher level, and only responds to requests from these higher levels. The higher level is always the client and initiates the data requests – the lower layer is always the server and courteously responds to the requests. The strict separation of levels, as well as the top-down approach of the information flow is softened and more and more flat models appear. For example, in a smart network every device or service must be able to initiate independent communication with all other services. 

The result of the working group is about OPC-UA client functionality out of the IEC 61131-3 controller: A controller can exchange complex data structures horizontally with other controllers independently from fieldbus system or vertically with other devices using an OPC-UA server call in an MES/ERP system in order to collect data or write new production orders to the cloud. It allows a production line to be independently active in combination with integrated OPC UA Security features.

An OPC-UA client functionality in a controller does not provide hard deterministic real time and so it’s not a deterministic fieldbus – but OPC UA provides fast and secure fieldbus independent communication, and provides modelling mechanism for information models.

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