Industrial Engineer · phase 3 of 16 · noun
Structured Text (ST)
IEC 61131-3 textual language used for expressions, calculations, loops, and structured control logic.
The Explain card
- Plain English
- Structured text is the typed language of the IEC family. It looks like Pascal, with IF, CASE, FOR and assignments, and it fits anything that is easier to write than to draw.
- Example
- A recipe lookup that steps through an array of setpoints and picks the one matching the product code is four lines of ST. In ladder it is a page.
- Why it matters
- Math, string handling, loops and structured data belong here. The cost is that maintenance cannot watch power flow through it the way they watch a rung, so keep it in well named blocks and leave the machine sequence in a language the floor can read.
- Hook
- When the rung would be a paragraph, write the paragraph.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
The PLC programmer used Structured Text to scale a 4 to 20 mA pressure input before sending the result to the pump-speed controller.
Why these words
- structured Latin structura, arrangement or construction modifies text to emphasize an organized form
- text Latin textus, woven material or written composition names the written medium
Where it came from
- Origin
- English technical compound formed from structured and text, ultimately drawing on Latin struere, to build, and texere, to weave
- Entered the language
- 1980s
- What changed
- Structure developed from physical construction to organized arrangement, while text shifted from woven material to connected written words; the compound became the standardized language name.
How it is spelled
- Pattern
- structured follows the silent-e pattern in which a word ending in e takes only d
- Pattern
- text retains the uncommon final consonant cluster -xt
Spelled like
- configured
- sequenced
- next
- pretext
Broken into chunks
-
struct
- construct
- instruct
- infrastructure
-
-ed
- configured
- sequenced
- organized
-
text
- textile
- texture
- context
What it sits beside
Same subject
- Ladder Diagram
- Function Block Diagram
- Sequential Function Chart
- programmable logic controller
Same shape
- structured data
- structured programming
- plain text
- source text
IEC 61131-3 programming languages
textual programming languages
Where it sits in the deck
Phase 3: PLC Program Organization and Execution
How the logic is arranged and how the scan actually runs it, which is the difference between code that works and code that works every time.
