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PLCopen XML Standard Update

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August 5, 2009 PLCopen finalized release 2.1 of the PLCopen Technical Committee 6 – XML Standard. This release 2.1 is based version 2.0 published in December 2008, as well as the feedback received from PLCopen members and the AutomationML organization.

PLCopen’s XML standard provides an open non-propriety linkage to other software that has not been available until now. The only option leading edge manufacturers had before this standard was to develop their own software creating interfaces to a single vendors proprietary control products. This could only be done on large projects at high cost and with the compromise of being tied to a single control vendor. PLCopen’s XML standard now provides an open playing field to lower costs and foster innovation in the same way open industrial networks, CAD interchange standards, OPC, and other standards have already done.

The PLCopen XML standard is an open interface for these other software tools, and provides the ability to transfer the information that is on the screen to other platforms. This screen information does not only contain textual information, but also graphical information. This can include the position and size of the function blocks, and how they are connected. The design of the ‘transferred’ program itself has to remain the same after the transfer, so not to be altered in look and feel.

The goal is to transfer a control project without much additional effort, from one development environment to another without loosing information even when it is incomplete, e.g. not compatible without errors. This of course is also valid for the POUs, and especially for the User Derived Function Block libraries. XML provides the right technology for this using an industry accepting interchange method.

This is more than an export / import tool from one development environment to another. All relevant information is exported. With this approach, PLCopen creates a complete new market, in which the focus is on reusability of software development from libraries up to complete control projects.

The standard allows the representation of a complete project within the IEC 61131-3 environment based on current XML technologies, including the common elements with Sequential Function Chart (SFC), the two textual languages Structured Text (ST) and Instruction List (IL), and the two graphical languages Function Block Diagram (FBD), and Ladder Diagram (LD). The formats are specified through corresponding XML schema. This is an independent file, with the .xsd extension, and as such part of this specification. The described formats are for the import and export of IEC 61131-3 Projects and Program Organization Units (POUs).

Concerning the exchange of graphical language constructs between different Programming Systems, the focus is on logical information with optional explicit graphics.

Using XML there are many possible uses for the PLCopen XML standard and these the “Use Cases” presently anticipated:

Use Case – Exchange format for programming tools (all IEC languages)

The exchange or POU(s) or complete projects.

(One time) migration to another system.

Parallel use of multiple systems.

Use Case: Interface to producers of graphical and logical information
In this case the XML scheme provides an interface to a producing tool. An example of such a producer is a high level engineering tool that creates graphics and logical information on FB, program, and /or project level. The producer of graphical and logical information will generate an XML file.
Use Case: Interface to consumer of graphical and logical information.
This use case provides an interface to supporting tools during the development phases, and is the counterpart of the use case above. Examples of consumers of information are validation tools, compilers, SCADA and HMI tools, as well as documentation generators; document management; source code database, version control, and document translation tools.

Use Case – Distribution format for function block libraries
This use case is focused to a format for distribution of (user derived) functions and function blocks specifically. With this, a user can create its own source library of their functions and function blocks as basis for different development systems.

The XML standard is becoming increasingly important due to innovations in Product Life Cycle Management (PLM), modeling and simulation software that enable virtual designs of machine, production lines and processes to avoid costly mistakes in actual implementation. The entire virtual plant and controls can be commissioned virtually to find problems before committing to real machines and controls reducing the time it takes to start manufacturing process and avoids costly rework at production startup time.

The PLCopen standard has been adopted by the AutomationML organization ( www.AutomationML.org ). This cooperation closes the gaps between production design (virtual factory) and the shop floor resulting in reduced time to market and lower costs for manufacturers. A number of PLCopen member companies are supporting the XML standard.

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Automation.com Real-time Information for the Automation Professional May. 25, 2012

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