Control Engineering Newsletter for Software -- February 2002

06/04/2002


In this issue:


 

Coming in Control Engineering

When you receive this, the January issue will still be posted on our web site. Look for the February issue in mid-month. In the cover article, I explore ways that technologies from the Internet are used in manufacturing. It is amazing how quickly these are being adopted. Read it when it hits the streets and let me know how much you are using these technologies or whether you plan to adopt in the future.

The January article on controllers by senior editor, Dave Harrold discussed the broad controller survey and trends in controller technology. My February controller article discusses specifying and applying controllers.

A comprehensive controller matrix with all the responding suppliers can be found at /archives/2002/ctl0102.01/020100matrix/CTL020100WE1.htm . Take a look and let us know your thoughts on the changing face of controllers. How have your control designs changed? Smaller controllers? More software intensive?

Reply to: gmintchell@cahners.com

 

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Feedback - programming and question of the month

I asked in January about programming and what languages you use. This started as reader feedback on using Visual Basic for control. There were many very thoughtful responses. Most readers report a preference of Ladder Diagram for typical control purposes. Only one writer used VB for control and doesn't now. While there are some C/C++ programmers, one person uses Delphi for control and HMI. Many think that programmers need to get organized and document their code.

Some quotes (edited for length):

'Control ideologies come from experience. I am primarily a PLC Ladder Logic proponent because that is what I have been exposed to. Even amongst the ladder logic community, people have their preferences from manufacturer to manufacturer. I think it is always interesting to learn and broaden one's understanding.'

'I am using IEC 61131 structured text language. We are doing PLC and motion with it. I used to program all kind of PLCs using ladder logic. I use VB for non-deterministic control tasks.'

'I feel that ladder, IEC 61131, or some form of function block programming are suitable for lower level controls. Ladder has been a standard for years in the U.S. and is suitable in diagnosis of machine and process control. VB is good for data acquisition and manipulation, as it does not make sense to use programmable controllers to accomplish this.'

'I've switched almost exclusively to Grafcet/SFC for sequential logic development. After the Grafcets are developed they can be implemented in almost anything, depending on the controller being used.'

'First of all I feel that you have to make a distinction between 'machine control programming' and 'supervisory control programming.' Machine control programming relates to the hardware aspect of control (turning motors on/off, sensing I/O devices, etc.). Supervisory control programming relates to the decision-making logic based on data, or the 'software' aspect of control still at real time (millisecond).

For machine control I still favor IEC-1131, of which Relay Ladder Logic is a component. For supervisory control programming, I feel that C or C++ is the most appropriate. It is better designed for the data manipulation and complex decision making than IEC-1131 languages. It also allows the use of databases for data access and information management.'

No one talked about Linux. Its popularity for use in servers is growing. Are you looking at servers to house all that manufacturing data you're collecting? Are you evaluating or using Linux for control?

Let me know what you use and why it's good at gmintchell@cahners.com

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Future of Ideas

The most important book I've read in a long time is Lawrence Lessig's 'The Future of Ideas.' For all who are concerned about who will control the Internet and the web, or just freedom in general, this book is a must read. Lessig is a professor of law at Stanford, but this does not read like a law book. The scholarship is great. Included are the origins of the Internet and the World Wide Web and the legal issues of copyright, patent, and intellectual property. He also discusses how the Internet has spurred innovation and how innovation in the future may be impacted.

'The Future of Ideas: the fate of the commons in a connected world,' is by Lawrence Lessig, Random House.

If you have thoughts on this topic, let me know. Oh, and Lessig's views? He's on the side of freedom of expression and innovation.

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Collaborative manufacturing software

I remember when setting up Rockwell's ControlView with a PLC 5 was a pain. You essentially had to type in tag names in ControlView to correspond to bits or words in the PLC. I thought that some of the newer programming editors that allow you to enter a tag once and use it everywhere were like heaven.

I pick on Rockwell Automation partly because that's what I was trained in and partly because it has released a product designed to go far beyond the integration needs of a single programmer. FactoryTalk is designed to provide the platform for integrated manufacturing enterprise data sharing. The components include a Directory providing a common namespace, Live Data providing services for data transfer, Audit tracks changes made to the system, Portal provides access to data and reports from a browser, and Data Model provides a framework to capture data about how a manufacturing process operates. Data Model is based on ISA's S95 specification.

Among the important features:

  • operations-based modeling approach

  • single view of the factory based on the ISA S95 specification

  • foundation for building multi-vendor solutions

  • consistent, neutral information infrastructure

The product wasn't up on the Rockwell Automation web site yet as I write this, but check back at www.rockwellsoftware.com .

For more on FactoryTalk from Control Engineering, see Feb. 1 'Today's News' at /archives/news/2002/February/mh0201a.htm

For more about ISA's S95 see www.controleng.com/archives/2001/ctl0101.01/010100.htm

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Design and modeling software for processes

I first wrote about One Step Generator (OSG) from Schneider Electric with input from Intellution in an article in December 2000 and followed up with some comments in July 2001. It is a design tool for process control systems and automation tasks involving networked PLCs and supervisory workstations. Using the S88 physical model to design system architecture, it generates code as Function Block Diagram and the supervisory system within Intellution's iFix. See www.gsia.org .

I recently caught up with product manager Paul Bennison. He relates that the product is still alive and well. The scope has been enhanced to include interface with Intellution's iBatch and iHistorian. It has also been integrated with Rebis Auto Plant P&ID software, which means that it can associate control loops in Rebis and generate software building blocks for control. Schneider is also working with ECT and its PromisE electrical schematic software allowing generation of PLC I/O card schematics.

This type of integrated design is something to keep an eye on.

For more about ISA's S88 standard, see Dave Harrold's article from April 1999 at /archives/1999/ctl0401.99/04g403.htm for S88

Further Control Engineering descriptions of OSG are found in a July 2001 article on integrated control at /archives/2001/ctl0701.01/010700.htm and a graphical modeling article in December 2000 at /archives/2000/ctl1201.00/001202.htm

 

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