Condition monitoring is a process of using a technology to detect changes in machine health over time in order to make a prognosis about when the machine will likely fail and to plan repairs or overhaul before that point. The frequency with which one takes measurements will depend on the machine, its current condition, and how quickly it typically degrades. Typically, one will test a machine more frequently (perhaps monthly) at the beginning of the monitoring program in order to develop a baseline and verify that the machine condition is stable. If the machine seems to be stable and healthy then the test frequency will be reduced to once quarterly for a typical machine.
If after a year or two, for example, the machine begins to develop problems one will want to increase the test frequency in order to better monitor changes in condition, perhaps down to monthly or once every two months. If the condition of the machine continues to worsen, but one wishes to wait as long as possible before overhauling it, then one should reduce the test frequency even more in order to detect any additional changes and avoid catastrophic failure. The important point here is that the test frequency depends on the machine’s typical failure rate and the test frequency should be adjusted as the machine begins to show signs of wear.