The use of proper minimum frequency and maximum frequency (hereinafter referred to as f-min and f-max) is crucial in order to have an adequate frequency range for seeing and identifying frequencies for the faults of interest, such as rolling element defects, rotor bar and stator slot pass, vane pass on turbo-machinery wheels, etc. Normally, setting an f-max around 50× turning speed for equipment running 30hz/1800 rpm or less, and 70× turning speed for equipment running 60hz/3600 rpm is adequate. The reason is that one would normally want to see at least the 6th or 7th harmonic of the highest generated bearing frequency, which is the ball pass frequency inner race, which is around 12 to 16× turning speed typical. This is usually the highest frequency of interest.

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