Industrial Engineer · phase 6 of 16
Major Fault
Serious controller or program fault that can stop task execution or place the controller in a faulted state.
The Explain card
- Plain English
- A major fault is a problem serious enough that the controller stops executing logic. Outputs go to their fault state and the fault light comes on.
- Example
- A routine indexes past the end of an array. The controller faults, the line stops, and the fault log records the type, the code, and which routine did it.
- Why it matters
- A major fault is a hard stop on the whole machine, so a bug that would be harmless on a laptop takes production down. Fault handlers can catch some kinds and let the controller continue, which is a choice that has to be made on purpose.
- Hook
- The controller would rather stop than guess.
Where it sits in the deck
Phase 6: PLC Operating Modes, Safety, and Diagnostics
Run, program and fault: what a controller does when something goes wrong, and the safety functions that decide how much that costs.
