Affect of background vibration

The Laser Doppler Vibrometer can measure the target without contact. It means the background vibrations (background noises) affect the measurement target and sensor separately.

The background vibration frequency is low but its displacement is unexpectedly big.

When you measure the target with high vibration frequency and minute displacement, it is difficult to detect accuracy and resolution as the dynamic range of indicator or analyzer is buried in the background vibration amplitude.

 

 

■The velocity detection for the target which has high background vibration frequency is more effective method.

We recommend the velocity detection rather than the displacement detection when the amplitude waveform is buried in the background vibration amplitude to increase the voltage range of FFT analyzer or oscilloscope.
Once measured by velocity, it is possible to covert to the integrated displacement
The velocity detection is advantage to the less affection of background vibration, it means the displacement of background vibration is high but
the velocity is low. The more high frequency, the more advantageous the velocity detection is.
For example, when the ultrasonic horn of ultrasonic welding machine is used;


  Frequency Displacement Velocity
Background vibration

5Hz

(peak)

 500μm
(half amplitude)
Approx. 16mm/s
Ultrasonic horn

60kHz

(sine wave)

1μm

(half amplitude)

Approx. 380mm/s

Compared background vibrations and ultrasonic horn, there is 500 times differences by displacement output.
The displacement of ultrasonic horn is output to be superposed by the big background vibrations.
The voltage range of analyzer will be set by background displacement, the analyzer is not able to detect minute displacement of horn.

 

 

While the measurement by velocity is able to set the voltage output as the measured target.
Once measured by velocity, it is more accurate to measure to covert to the integrated displacement with FFT analyzer.
The velocity detection for the target which has high vibration frequency and minute displacement is more effective method.


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