How to Calculate F-MAX

Do you know how to calculate F-MAX or even what F-MAX is? Knowing how to calculate F-MAX is an important part of vibration analysis because many different types of faults can be shown at multiples of the running speed, which is otherwise known as 1x.

But first, what is F-MAX?

F-MAX means “Frequency Max.” This is the maximum frequency range used when capturing vibration data on a spectrum.

For example, with a rolling element bearing, F-MAX should be set to 70 times the run speed.

Why F-MAX should be set at 70 times the run speed ?

The reason why F-MAX should be set at 70 times the run speed is because bearing default frequencies are different for each bearing type and number. These differences are based on the bearings’ geometric construction. This means that we need to ensure enough defect frequencies are being captured to generate a fault in the software based on predefined bearing bands and alarm values.

Another reason why F-MAX should be set at 70 times the run speed is due to the electrical nature of the machine. It is helpful to collect data that includes rotor bar pass frequencies and their sidebands for determination of some electrical fault types.

For machines with a gearbox, however, the general rule is different. On these machines, the general rule is to set F-MAX at 200 times the run speed.

If the number of teeth in the gear are known, the formula is 3.25 times the teeth number, multiplied by the RPM.

An example of this would be if the number of teeth was 17, and the RPM was 1750, F-MAX would be 97,000x.

Calculating F-MAX will also be different if you are using the ACCUREX auto-diagnostic software, which is what our FALCON and SMC use. Bearing defect determination via ACCUREX is accomplished with the use of an algorithm rather than bearing bands. ACCUREX uses the full time period of the waveform in order to determine faults, instead of using only a portion (bands) of the spectral data.

by Bertrand Wascat | | August 14, 2019
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