Industrial Engineer · phase 3 of 16
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.
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.
