Industrial Engineer · phase 4 of 16 · noun

Local / Global Tag

Tag scoped to one program or made accessible across the controller project.

The Explain card

Plain English: A global tag is visible to every program in the controller, and a local tag belongs to one program and is invisible outside it. The scope decides who can read and write it.
Example: Plant_Estop is global because every program needs it. Filler_Step is local to the Filler program because nobody else has any business changing it.
Why it matters: Keeping tags local is how two programs avoid stepping on each other, and it is how a program can be copied to another controller without dragging a hundred dependencies along. Global by default is convenient for a week and a mess for a decade.
Hook: Who is allowed to know.

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

During commissioning, the conveyor routine moves the photoeye state from a Local tag to a Global Tag for HMI display.

How it is built

Where it came from

Origin: Middle English local, from Late Latin localis, based on Latin locus, meaning place
Entered the language: 15th century
What changed: The word moved from physical place to nearby operation, then gained specialized uses in computing and automation.

How it is spelled

Pattern: The ending -al marks a word formed with the common relating-to suffix.
Pattern: The letter c before a keeps its hard /k/ sound.

Spelled like

Broken into chunks

What it sits beside

Same subject

Same shape

tag visibility terms

PLC tag types

Phase 4: PLC Memory, Tags, and Instructions

The data a program moves and the instructions that move it, from a single true or false value up to a structured array.