ONO SOKKI Application - Measuring natural vibration frequency and damping ratio by hammering test

FFT Application

FFT

Vibration analysis

FFT V-1-1

Measuring natural vibration frequency and damping ratio by hammering test

This example shows how to measure natural vibration frequency and damping ratio etc. Suspend a measurement object in a free vibration (or place it on something soft) and perform hammering test by the GK-3100 Impulse hammer. And then detect the free damping vibration by an accelerometer. The DS-3000 series calculates the frequency response function of acceleration (A) and hitting force (F) by applying them to the following calculation, and obtains the resonant frequency at the peak of (A) / (F). (In this example, the peak value of (A)/(F) equals to the resonant frequency, natural vibration.)
Frequency response function = Acceleration (A) / Hitting force by the GK-3100 (F) (Accelerance < Inertance >)
You can see several peak values depending on a shape of a measurement object. Damping ratio also can be calculated by using half-power bandwidth method. Moreover, integrating function of the DS-3000 series enables display and evaluation of velocity/power (mobility), displacement/force (compliance), force/acceleration (dynamic mass), force/velocity (mechanical impedance) or force/displacement (dynamic rigidity).

Model	Product name	Remarks
DS-3000 series	Multi-channel Data Station	DS-3204 4ch Main unit DS-0321 FFT Analysis function DS-0350 Recording function USB 3.0 Cable (2 m)
GK-3100	Impulse force hammer	Frequency range:: up to 8 kHz, resonance frequency: 31 kHz, hammer cable (3 m) & signal output cable (0.9 m) (included)
NP-3211	Accelerometer with built-in preamplifier	Ultra compact, lightweight (0.5 g), frequency range: 0.3 Hz to 20 kHz ±3dB, signal cable (3 m) (included)
NP-0020	Signal cable extension adapter	The adapter for signal cable extension (between the NP-0153 and the cable for the NP-3211).
NP-0153	Signal cable for the NP-0020	5 m, -25 to +160˚C
NP-0021	Miniature/BNC conversion connector	Converts the NP-0153 signal cable terminal to BNC connector and input to the DS-3000 series BNC connector.

Remarks
The DS-3000 series needs a PC separately.
Other models of FFT analyzer can be applicable (the DS-3000 with tracking analysis function, octave analysis function, the CF-3650/3850, the CF-7200A, the CF-9200/9400 series).