engineering

Structured text

Structured text is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Structured text rather than just read about it. In short: Structured text, abbreviated as ST or STX, is one of the five languages supported by the IEC 61131-3 standard, designed for programmable logic controllers (PLCs). It is a high-level language that is block structured and syntactically resembles Pascal, on which it is based.

Key takeaways

Structured text belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Structured text to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Structured text from memory before moving on to harder problems.

Reference excerpt

Structured text, abbreviated as ST or STX, is one of the five languages supported by the IEC 61131-3 standard, designed for programmable logic controllers (PLCs). It is a high-level language that is block structured and syntactically resembles Pascal, on which it is based. All of the languages share IEC61131 Common Elements. The variables and function calls are defined by the common elements so different languages within the IEC 61131-3 standard can be used in the same program. Complex statements and nested instructions are supported:

Iteration loops (REPEAT-UNTIL; WHILE-DO) Conditional execution (IF-THEN-ELSE; CASE) Functions (SQRT(), SIN())

Sample program

Unlike in some other programming languages, there is no fall through for the CASE statement: the first matching condition is entered, and after running its statements, the CASE block is left without checking other conditions.

Additional ST programming examples

Function block example

References

Worked examples

Example 1 — a first encounter with Structured text

Start with the simplest possible case. Write down what Structured text claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Structured text before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Structured text ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Structured text

In research: Structured text appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Structured text in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Structured text is common in secondary-school and first-year university syllabi. It links to neighbouring topics IEC standards, Pascal programming language family, Programmable logic controllers, so understanding it makes those chapters shorter.
In everyday life: Look for Structured text outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Structured text in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Structured text means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Structured text out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Structured text in simple terms?

Why does Structured text matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Structured text?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Structured text.