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Fixed-Interval
One of a variety of different types of intervals (time periods) between events.

In time-based maintenance, this is a strategy that relies upon clearly defined frequencies for maintenance events.


A fixed schedule generally results in the work being done at the same time each calendar year.

Some examples of fixed interval activities for routine maintenance, include:  
  • “Lubricate pumps every 2,000 hours”;
  • "Wash the windows twice a year". 
There are two types of fixed intervals:
Some examples of fixed interval task for major maintenance include:
  • Replace batteries on the emergency generator every 4 years
  • Conduct elevator safety tests every 5 years
  • Conduct hydrostatic tests of extinguishers every 6 years
  • Replacement of pressure relief valves every three years
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Fig 1. Fixed interval events that are uniform at 3-year spans, with escalation.


Fixed interval events that are clustered
Fig 2. Variable interval events that are clustered, with escalation


fixed interval events mapped onto the P-F curve to illustrate the relationship between time and resistance to failure
Fig. Fixed interval events mapped onto the P-F curve to illustrate the relationship between time and resistance to failure.


Fixed Interval with Delayed Start AssetInsights.net
Fig 3. Fixed interval (shown in "green") with delayed start (shown in "red").

See also:
Compare with:

I Care is juggling various cycles (seasonal, fiscal, meetings, maintenance and renewals)
Fig. I. Care is juggling various cycles (seasonal, fiscal, meetings, maintenance and projects).

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