18
Window function
：
Hanning window
Frequency span
：
20kHz (Acceleration),200Hz or 500Hz (Envelope)
Number of analysis lines
：
Set up so that the frequency resolution becomes narrower than 1Hz
Operation type
：
It is used if necessary
An example of outer race defect of a bearing
：
The Ball Pass Frequency of Outer race can be observed at 77.8Hz.
5.3 Measurement of natural frequency
The natural frequencies of a structure can be measured by exciting the object. Attach an accelerometer to the
object, and excite it with an impulse hammer. In measurement, it is necessary to use the trigger function and the
linear average. Refer to the instruction manual of VA-12 about the details of the trigger function. When an
exciting point and an attached point of the accelerometer changes to the other position, the measured frequencies
may change. In this case, all the measured frequencies are considered as natural frequencies.
Fundamental settings
Sensor selection
：
PV-57I (in usual case),
A lighter accelerometer for example PV-91C (when the object is very small and light)
High-pass filter
：
10 Hz
Low-pass filter
：
20 kHz
Analysis function
：
FFT Analyzer Mode
Measurement data type
：
Acceleration
Window function
：
Rectangular window
Frequency span
：
5 kHz
（
Set up so that the whole natural frequencies are included
）
Number of analysis lines
：
3200
（
Set up so that the whole decay process of a time waveform can be
observed
）
Operation type
：
Linear average
、
Average number
：
about 5
FFT (envelope)
Time waveform
(acceleration)