Electromechanical

Text Etiquette in the IEC61131 Programming Language

Text Etiquette in the IEC61131 Programming Language - Structured Text - Parker Hannifin Electromechanical We are not here to tell you the rules about everyday texting: while driving (never!), during meetings (with caution) or sending photos (with extreme caution!). On the contrary, we want to talk about Structured Text, which is a favorite IEC61131 programming language. If you are someone who started off with BASIC and Pascal, then moved to Visual Basic before sampling a variety of Basic-like motion languages, Structured Text (ST) may be in your comfort zone.

Writing code with complex evaluations

ST includes many familiar commands like WHILE loops, IF-THEN-ELSE blocks, FOR loops and the very useful CASE statement. In most IEC61131 platforms like the ACR9600 series, you will also find a full set of built-in functions for math operations (SIN, SQRT), string manipulation (LEN, LEFT) and data type conversions. When it comes to writing code with complex evaluations, ST is easier and more efficient than the graphical languages like ladder. 

Structured Text acts like a PLC

But now for the important thing to remember: ST acts like a PLC! You need to consider that the code will scan and run over and over, without stopping and without the need for looping. A common practice in many motion text languages is to dwell or wait for an event to happen before moving to the next line of code. You won't find the dwell or wait statements in ST and please do not try to create them! A PLC program should be designed so that it completes in a finite and fairly short and consistent time. 

That said, resist the urge to create a WHILE loop that spins in place until a condition is met, such as an input being pressed by an operator. That could take seconds or even minutes. If the ST code is "waiting" for that input, the task will not complete. In many cases, other tasks will not run and background services required for communications will be stalled. Instead of waiting for that event, let the task run freely and evaluate that input condition each scan with, say, an IF statement. Once the condition evaluates true, the code can take the next step in the machine operation.

Remember to keep both your text messages and PLC programs short and clean. You don't want the machine to slow down. 

 

Text Etiquette in the IEC61131 Programming Language - James Willey Parker HannifinArText Etiquette in the IEC61131 Programming language - Mario Mitchellticle contributed by Jim Wiley, Applications Engineer, and Mario Mitchell, Product Manager, Electronic Business Unit, Electromechanical Automation North America, Parker Hannifin. This was originally posted on the Parker Motion blog August 3, 2011.

 

 

 

 

Related posts on motion control solutions.

How to Remotely Control Your Plant With a Mobile App

Developing Custom Motion Control Solutions

You Don’t Need a Cloud for IIoT! Just a Centralized Control Scheme

Is Industry 4.0 Driving the Need for Smarter Motion Control Products?

 

 

 

 

 

 

Categories
Recent Posts by Author

High-load Rodless Actuators Powering the Factory Automation Revolution

The arguments advocating more automation in our factories and process plants are gaining momentum and translating into a revolution in production environments.  Parker designs automated linear motion...

Shift in Linear Actuator Design Fueled by Newer Generation

It’s no secret that the Millennial Generation’s practices and preferences are shifting consumer product design and marketing messages across the board. But how does that trend affect product design in...

Automated Bottle Sorting | Simplifying Returnable Assets

Most people of a certain age have childhood memories of returning beverage bottles to their neighborhood store and getting back their deposit coins, which were usually just enough to invest in an...
Comments

Have a question about Parker products or services? We can help: Contact Us!

Comments for Text Etiquette in the IEC61131 Programming Language


Please note that, in an effort to combat spam, comments with hyperlinks will not be published.

Leave a comment





Captcha