The P-F interval: what it is and how to use it
The P-F interval is the time, running hours, or cycles between a detectable potential failure (P) and the functional failure (F) you are trying to avoid. An on-condition or predictive task has to be done on an interval shorter than the P-F interval you believe you have — with enough margin that you can still act — or the warning will arrive between inspections, or too late to use.
Two common mistakes: treating a vendor’s “typical” P-F interval as a measurement of your machine, and setting a route frequency from technician availability rather than from the failure mode. If you do not know the interval, say so, use a conservative assumption, and look for data (history of detected defects, known degradation rates, or a trial period with a tighter route) rather than inventing precision.
Not every failure has a useful P. Some modes go from healthy to failed with little warning. Those modes need a different task type, a redesign, or a run-to-failure decision, not a tighter vibration route. That is the same task-selection logic you will meet in RCM and in PdM program design.