Schneider Electric makes XML sources available to PLCopen

Hannover, Germany - Clive Smith, representing Schneider Automation, presented to Eelco van der Wal, managing director of PLCopen, XML sources for converting graphical PLC languages to XML format along with the preliminary draft of a 49-page technical specification XML Formats for Graphical Languages that details their implementation.



Clive Smith (left), Schneider Electric, presents XML sources to PLCopen managing director Eelco van der Wal at Hannover Fair.

Hannover, Germany - Clive Smith, representing Schneider Automation , presented to Eelco van der Wal, managing director of PLCopen , XML sources for converting graphical PLC languages to XML format along with the preliminary draft of a 49-page technical specification XML Formats for Graphical Languages that details their implementation.

The "XML sources" that Schneider has donated are a set of definitions that describe how elements from the three graphical PLC languages-Function Block Diagram (FBD), Sequential Function Chart (SFC), and Ladder Diagram (LD)-can be described in XML format. The specification, which is being distributed to PLCopen members, will remain an internal document until members decide what to do with it. It is said to provide XML definitions for all elements of all three graphical languages.

Mr. Smith said Schneider Automation has been working on the XML sources for some time as a means of bridging the software from various programmable controller product lines in his company. Schneider currently supports April, AEG, Modicon, and Telemecanique PLC brands as well as SyMax, a Square D controller in the U.S.A.

Mr. van der Wal said that, as a result of Schneider's donation, a new technical committee called TC6 - XML will be formed to evaluate the materials.

"In reality this means that the XML sources, as being provided now by a single source, will be tested and adapted to a quite extensive set of tools and suppliers. This is an excellent fit with the idea of XML, and is of particular interest for the graphical languages."

The TC6 - XML technical committee will hold its first meeting on 26 June, at Schneider's Seligenstadt office in Germany. There will be about 15 to 20 representatives of the major PLC and software companies at the meeting. The proposal for Schneider to donate the materials was made at PLCopen's general assembly in June 2001 at Infoteam in Germany.

"Schneider Electric has laid the groundwork," commented Mr. van der Wal. "How well it will fit into our systems remains to be seen. That is for the TC6 committee to decide. They may consider the document nearly complete and require only a few amendments, or they may want to set up individual task forces to investigate more closely certain areas. We definitely won't be publishing anything until after the June meeting.

"If nothing else, it will be good feedback for Schneider," said Mr. van der Wal.

PLCopen goals

The goal of IEC 61131 was to provide harmonisation of the representation of PLC programming languages across various brands, not specifically to provide code portability among different vendors' PLCs. Portability has been more in the hands of PLCopen.

But PLCopen's ambitions of portability has been difficult to achieve, and in reality, has only been partially realised by exchanging code compiled in Instruction List (IL). It is quite difficult to translate from one graphical language to another, and attempts to do this have involved IL in combination with C or C++, or C language code by itself. "There is probably more C code going between PLCs than anything else," admits Mr. van der Wal.

He said PLCopen members are very much interested in the XML specification, because it provides a way to solve the exchange within graphical languages "which is now 10 years under discussion, and not solved.

"If you create a graphical program in one environment, export it, and import it in another environment, you want to see a similar program," said Mr. van der Wal. "As much as possible, the graphical construct should be the same on both systems.

"Take FBD, for example. For FBD it means that the size, positioning, order, and the way the connections go, should be the same on both systems. To do this one needs extensive graphical information, far beyond what IL, or any compiled code, can provide."

The next possible step: "Since XML code can be represented in any browser, this means any browser will be able to 'see' the same graphical program. It cannot change the program, because it is not an editor. But if you store the program in XML code on your target system, this means you can check it with any browser," he said.

"Also, independent XML code gives the possibility of having a separate graphical editor with the compiler part. The editor could be something like Microsoft Visio. And the compiler can be a component running somewhere on the web - or even in the PLC," he added.

"Overall, if we succeed, this certainly creates a basis for different architectures in the field."

Control Engineering Daily News Desk
Michael Babb, editor, Control Engineering-Europe

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