Industrial Engineer · phase 6 of 16
Redundancy / Hot Standby
Architecture using a synchronized backup controller or component that can assume control after a primary failure.
The Explain card
- Plain English
- A redundant system keeps a second controller running in step with the first, ready to take over the moment the primary fails. Hot standby means it is powered, synchronised and current, with no restart needed.
- Example
- A water treatment plant runs paired controllers with a fibre link between them. The primary loses power, the secondary takes control in a fraction of a second, and the pumps never change speed.
- Why it matters
- Redundancy buys availability, and it buys complexity, since I/O has to be reachable from both sides and a switchover that was never tested is a switchover that will not work. It is for processes where a stop costs more than the second controller.
- Hook
- Two pilots, one of them ready to grab the stick.
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.
