Glossary · ISA-18.2
What is ISA-18.2?
The alarm management standard for process industries: the alarm lifecycle from design to review, and the alarm rates considered acceptable.
The core principle is that every alarm must call for an operator action. An alarm the operator can do nothing about is not an alarm, it is information.
The standard puts numbers on it: no more than two alarms an hour in steady state, and fewer than ten in the first ten minutes of an upset. Meeting that needs on-delays, deadbands, priorities and suppression of consequential alarms.
Related terms
- Alarm deadband
- A gap between the value that raises an alarm and the value that clears it, so the alarm does not chatter around the trip point.
- On-delay timer (TON)
- A standard function block whose output Q becomes true after IN has stayed true for PT without interruption, and resets as soon as IN drops.