A lot of facilities assign condition monitoring intervals based upon arbitrary schedules such as 30,  90, 180 or 365 days. Often, this is due to a lack of understanding of how equipment fails, misunderstanding of how conditional tasks such as vibration analysis work, available labor, and lack of importance placed upon condition monitoring efforts. These arbitrary collection intervals can actually lead to failures that go undetected and a loss of value from the effort.

To appropriately determine monitoring intervals, a couple of things should be known. First, the point in time (P) that the potential failure becomes detectable must be known (detected with vibration monitoring, for instance.) Second, the time (F) at which the potential failure would degrade to a functional failure must be known. This difference in time (P-F Interval) is the window to take corrective action and avoid the negative consequences of the failure. This difference in time will determine how often conditional tasks such as vibration monitoring must be done to detect potential failures from such things as bearing issues, etc. Typically, the monitoring interval would be set to half of the P-F interval. This allows enough time for the technology to detect the problem and for corrective action to be taken. However, in certain circumstances, it may be necessary to collect data at shorter intervals than half of the P-F interval.
It is important not to assign monitoring intervals based upon gut feelings, arbitrary calendar intervals, and so forth. Let the equipment tell you how often monitoring must be completed. Not understanding the process above can lead to costly results!