Posted by: Harold Ennulat | September 20, 2010

OPC UA -> PLCopen Interoperability Demonstrated

The OPC and PLCopen foundations have been working together with HMI, PLC and even MES System vendors and have rolled out version 1 of a new open PLC communications standard that implements IEC 61131-3 PLC programming in a platform independent way.  OPC UA is the standard by which PLCs, HMIs, and MES systems can communicate with each other.

The new OPC standard suite is called collectively OPC UA.  UA stands for Unified Architecture.  Among other things, OPC UA attempts to define a mapping of data so that vendors can communicate much more easily to each other.

A very good introductory video of OPC UA on YouTube can be viewed at: and an introductory recorded webinar on OPC UA in connection with PLCopen, presented by 2 of the OPC UA developers, can be viewed at

The example shown in the webinar shows 6 HMI vendors talking to 6 different PLCs each running an identically structured boiler control program.  Each HMI contained a matching faceplate screen for the boiler control that required only that one data structure was mapped (a single click and drag operation) from each PLC to the HMI and that 6 instances of the template HMI screen be created for each selected data structure.  The webinar suggests that PLCs will likely have the OPC UA server built in but will also be able to use dedicated OPC UA servers for systems with a lot of HMI’s accessing a single PLC.

The old OPC specifications are now called OPC Classic or OPC COM since they are based on Microsoft DCOM communications specification and drivers.  OPC UA is now based on .NET communications and is no longer dependent on operating system functionality directly like DCOM drivers are.

The OPC foundation is making tools and training available to migrate OPC Classic applications in the new OPC UA format.

While OPC UA version 1 has now been officially released it currently appears to only supports structured Text (ST) which is only one (1) of the 5 IEC 61131-3 PLC languages.  For Data Access typical in HMI to PLC communications this does not matter, however the plan is to implement the full IEC 61131-3 PLC programming capabilities using OPC UA as the communications interface between PLCs and PC based programming tools.  This gives OPC UA a much longer reach than OPC Classic.

Final Thoughts

OPC UA and PLCopen are what consumers (controls engineers and end users) are looking for, as this makes PLC platforms increasingly a commodity which should continue to drive control solutions down in costs.  Making the communications configuration and programming efforts more streamlined will also serve to reduce control systems costs.  This can not come to soon.  However it will take some time for a critical mass to build before products based on these standards will effectively compete with the likes of PLC giants like Allen-Bradley and Siemens.  If these 2 major suppliers get on board with this then things should move very quickly to get more solutions using the OPC UA and PLCopen standards.  For now it appears to be some key smaller players seeking to gain competitive advantage in an arena that for now at least does not include Allen-Bradley (Rockwell Automation) and Siemens.


The key organizations working together on OPC UA <-> PLCopen functionality are:  supplier of SDKs and tools for developers

For a list of OPC UA videos and webinars see

Additional Information about OPC UA and PLCopen communication see the links at

Updated: September 30, 2010 10:12am  |  Created: September 16, 2010 1:58pm CST for Publishing September 20, 2010


  1. For a definition of OPC see the end of the article at:

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