Definition:
Demand Interval (DI) is the inverse of demand rate. It is expressed in time based units as for most people this is more intuitive than a rate.
This is not a formal term defined by IEC 61511-1. The inverse term demand rate is the proper IEC term. DI is used by some practitioners for specific pieces of guidance.
Key Points:
- Expressed as year between demands.
- DI is the inverse of demand rate.
Example:
A process that sees a potential overpressure event once every five years has a Demand Rate of 0.2 demands/year. This would be a low demand mode. It’s DI would be 5 years.
See also: mode of operation, demand rate