CEMB USA N300 - Manual (Page 27)

Vibrometer function 5 - 3
5. Type of vibration
Like all physical sizes, vibration has a value that can vary from one moment to the next;
mathematically it can be described by a function of time. Its overall value can therefore be
calculated in three different types:
− RMS (Root Mean Square): mean square value
the mean value of the previously squared vibration;
the most commonly used, especially for acceleration or velocity measurements. It is
a direct indication of the vibration’s “energy” content: in practice it represents the
power brought with the vibration and discharged onto the supports or bases of the
vibrating structure.
− PK (Peak): peak value
the maximum value reached by the vibration in a certain period of time.
− PP (Peak-to-Peak): peak-to-peak value
the difference between the maximum value and the minimum value reached by the
vibration in a certain period of time;
normally used for movement measurements.
6. 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