Industrial Engineer · phase 3 of 16 · noun

Sequence / State Machine

Logic that advances equipment through defined operating states based on commands, conditions, and transitions.

The Explain card

Plain English: A state machine holds the machine in one named state at a time and moves to the next only when a defined condition is met. Each state decides which outputs are on.
Example: Idle waits for start, Filling runs the pump until the level is reached, Mixing runs the agitator for two minutes, and Draining opens the valve until empty before returning to Idle.
Why it matters: A machine with a single state variable can always answer the question of where it is and why it stopped. Logic without one tends to have three phases fighting over the same valve and a technician guessing which won.
Hook: One number that says exactly what the machine is doing.

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

In a sentence

The PLC sequence starts the conveyor after the guard circuit is healthy, waits for the photoeye, and then advances to the indexing step.

How it is built

Where it came from

Origin: Middle English from Old French sequence and Medieval Latin sequentia, from Latin sequi, meaning to follow
Entered the language: 14th century
What changed: It first referred to a continuation or liturgical passage, then to an ordered succession, and later to stepwise program organization.

How it is spelled

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Broken into chunks

What it sits beside

Same subject

Same shape

step-control terms

sequence implementations

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.