CEMB USA N100 - Manual (Page 27)

Vibrometer function 5 - 3
5. Units of frequency
Indicates how to display the velocity and frequencies, and can be chosen from:
- Hz – cycles (revs) per second
− RPM – revs per minute
Note:
The relation 1 Hz = 60 RPM clearly exists between the two units
Settings only valid for overall measurements
1. Frequency range:
The overall vibration value usually originates from the sum of various contributions, caused
by various phenomena, which are therefore associated with different frequencies.
Depending on the situation, you may only wish to consider those corresponding to a
certain range of frequencies in overall measurement:
− 1-100 Hz if the interest is limited to phenomena with low frequencies
− 2-200 Hz if the interest is limited to phenomena with relatively low frequencies
− 5-500 Hz if the phenomenon also involves average frequencies
− 10-1000 Hz to comply with the conditions set forth in the ISO 10816-1 standard
(typical)
Note:
A commonly used practical consideration is to check that the maximum frequency
is set to at least 20-30 times that of the rotation of the shaft examined. This means
that even the high-frequency zone, where bearing-related problems usually occur,
can be included in the spectrum.
Note:
Other things being equal, the selection of a low maximum frequency (less than
1000 Hz) considerably lengthens the amount of time required for acquisition and
measurement.
2. No. of averages
Shown next to the N symbol, it indicates the number of spectrums that must be calculated
and averaged to increase the stability of the measurement. All values between 1 and 16 are
acceptable, but 4 averages are more than enough for normal vibration measurements on
rotating machines.