One core activity on which his organization focuses is the International Electrotechnical Commission’s (IEC, www.iec.ch) “Standard 61131, Programmable Controllers,” particularly “Part 3, Programming languages.”
The best benefit users derive from IEC 61131-3 is its structured approach to software development, van der Wal believes. Programming now involves a group of people with different disciplines or backgrounds. “And that means there are people in software development, process, maintenance, installation and elsewhere for whom you have to provide a software tool with which they feel comfortable. IEC 61131 provides such an environment,” he says.
Perfect sense
This standard is the basis for nearly every new project, says Rob Dussault, automation product manager for Schneider Electric’s U.S. automation operations (www.schneiderelectric.com), located in North Andover, Mass. “The concept of 61131 makes perfect sense. By adopting this standard, end-users are free to choose any compliant, best-in-class automation vendor.”
There are two current industry trends, says Dussault. One is a distributed programming environment. What had been missing in distributed control systems (DCSs) was the software to connect devices, he explains. “Now we put the intelligence into one piece of software, press a button and it figures out where it is supposed to reside in the automation architecture.”
The second trend is that end-users want staff to know many programming languages, states Dussault. Traditionally, end-users standardized on one vendor. That led to use of outside contract services or resources from elsewhere in a company. It also limited end-users’ selection of the best-in-class machinery from original equipment manufacturers, he says.
This new situation has led end-users to move to standard object-oriented programming, Dussault explains. Implementing that comes through the function-block diagram, which is a language supported by IEC 61131-3, he notes. Object-oriented functionality also makes it easier for maintenance staff to identify process problems, he says. “The operator and the maintenance people will feel more comfortable with such a standardized environment,” adds van der Wal. “Also, there is major cost and risk reduction for a machine. For installation, time is reduced from weeks to days.”
The IEC standard finds use in the Dallas office of Camp, Dresser & McKee Inc. (www.cdm.com), a full-service consulting, engineering, construction and operations firm. It currently uses IEC 61131-3’s programming environment on municipal water/wastewater projects throughout the Southcentral United States, says Rick Hildago, a Dallas-based instrumentation and control specialist. He notes that CDM uses Schneider Electric’s Concept software.
Remote heartbeats
“On some projects, we have standardized on the format for the various sections that encompass an overall PLC program,” he says. In addition to the process-specific control logic, other sections are developed for specific functions such as monitoring of a remote PLC’s heartbeat for peer-to-peer communication, monitoring of PLC diagnostics information, data packing/memory mapping and the like, Hildago notes.
The development of each section can be assigned to individual programmers, says Hildago. Once programming is completed, the team can merge a section into the overall program of each PLC, as needed. “This allows for a standardized section to be used throughout the entirety of the plant and reduces the program development time, because the logic is only created once,” he explains.
IEC 61131 ensures that the programming environment is on an even playing field for all vendors, Hildago believes. “End-users can now use specific vendors’ hardware features to determine the appropriate technical and cost-effective solutions for their needs.”
Kenna Amos, [email protected], is an Automation World contributing editor.
