Choose the right programming language

Which language should you choose for use with your programmable controller? Among the five languages defined in IEC 61131-3, generally ladder diagrams or ladder logic is most widely applied in North America. Other languages have practical applications and should not be overlooked. Choice depends on programmer's skill, the programming task, the level and structure of the problem and control syst...

07/01/2003


Which language should you choose for use with your programmable controller? Among the five languages defined in IEC 61131-3, generally ladder diagrams or ladder logic is most widely applied in North America. Other languages have practical applications and should not be overlooked. Choice depends on programmer's skill, the programming task, the level and structure of the problem and control system, who needs to interact with the program, and, perhaps, how often it's modified.

Since inception in 1992, PLCopen has helped promote and support programming standards, which allows, the association says, for less training, more logical organization, modularization, and use of modern software techniques. "Each program is structured, increasing its reusability, reducing errors, and increasing programming and user efficiency," according to the group.


Four languages describe the same piece of code.

"Also, the standard allows two ways of developing your program: top down and bottom up. Either you specify your whole application and divide it into subparts, declare your variables, and so on. Or you start programming your application at the bottom, for instance via derived functions and function blocks. Whichever you choose, the development environment will help you through the whole process," PLCopen says.

The five elements of IEC 61131-3 are:

  • Sequential function charts (SFC)—Rather than a language, SFC is more of a graphical method of organizing control programs.

  • Ladder diagram (LD)—most used in North America, it graphically represents rungs of contacts, coils, and special instruction blocks. Its origin is relay-ladder logic.

  • Instruction list (IL)—a text-based language similar to assembler. This is the European counterpart to LD.

  • Structured text (ST)—a text-based language similar to Pascal.

  • Function block diagram (FBD)—a graphical language corresponding to a circuit diagram. FBD is widely used in process industries.

Other resources

Several IEC standards provide more information about function blocks: IEC 61499 and IEC 61804, which focuses on the process industry. Function blocks encapsulate algorithms so they can be more easily understood and applied by those who aren't software specialists.

For more on function blocks, see www.controleng.com/issues , 2002, September, "Component Automation Enables Modeling and Control." Also, in the August 2003 issue, look for an article on multiple-platform programming software. See related items at www.controleng.com/tutorials.

IEC, at www.iec.org , publishes "Programmable controllers - Part 3: Programming languages." IEC 61131-3 "specifies syntax and semantics of programming languages for programmable controllers as defined in part 1 of IEC 61131." Price is about $205. A related IEC publication is "Programmable controllers - Part 8: Guidelines for the application and implementation of programming languages."

PLCopen, at www.PLCopen.org focuses on control programming and participates on technical committees to evolve programming standards.

Comments email MHoske@cfemedia.com



Pros and cons of IEC 61131-3

Benefits and drawbacks of IEC 61131-3 include the following, according to Wolfgang Langer, Schneider Electric software product manager:

Benefits are:

Less retraining costs—IEC looks and feel similar among vendors;

Greater focus on problem solving and software reusability;

Fewer misunderstandings and errors in programming when switching between languages; all IEC languages work the same; and

Greater community—many tools from independent suppliers can be used. PLCopen drives IEC standard with vendors to comply with interoperability standard.

Drawbacks include:

Too many optional features;

Does not define implementation limitations for the size of a page value to define a program;

Doesn't define the minimum of subsets needed to implement;

Doesn't define minimum limitations while implementing, such as how many rungs must be supported in one section; and

Doesn't define conversion among languages.

David Greenfield dgreenfield@reedbusiness.com



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
2015 Top Plant: Phoenix Contact, Middletown, Pa.; 2015 Best Practices: Automation, Electrical Safety, Electrical Systems, Pneumatics, Material Handling, Mechanical Systems
A cool solution: Collaboration, chemistry leads to foundry coat product development; See the 2015 Product of the Year Finalists
Raising the standard: What's new with NFPA 70E; A global view of manufacturing; Maintenance data; Fit bearings properly
Special report: U.S. natural gas; LNG transport technologies evolve to meet market demand; Understanding new methane regulations; Predictive maintenance for gas pipeline compressors
Cyber security cost-efficient for industrial control systems; Extracting full value from operational data; Managing cyber security risks
Drilling for Big Data: Managing the flow of information; Big data drilldown series: Challenge and opportunity; OT to IT: Creating a circle of improvement; Industry loses best workers, again
Migrating industrial networks; Tracking HMI advances; Making the right automation changes
Understanding transfer switch operation; Coordinating protective devices; Analyzing NEC 2014 changes; Cooling data centers
Upgrading secondary control systems; Keeping enclosures conditioned; Diagnostics increase equipment uptime; Mechatronics simplifies machine design

Annual Salary Survey

After almost a decade of uncertainty, the confidence of plant floor managers is soaring. Even with a number of challenges and while implementing new technologies, there is a renewed sense of optimism among plant managers about their business and their future.

The respondents to the 2014 Plant Engineering Salary Survey come from throughout the U.S. and serve a variety of industries, but they are uniform in their optimism about manufacturing. This year’s survey found 79% consider manufacturing a secure career. That’s up from 75% in 2013 and significantly higher than the 63% figure when Plant Engineering first started asking that question a decade ago.

Read more: 2014 Salary Survey: Confidence rises amid the challenges

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.