Strange vibration shaker acceleration frequency response test result

[flyeagle]

Hi There,
I have a VTS(vibration test system)-100 shaker. To make sure it works correctly, I have done a acceleration frequency response test for the bare shaker. In which, I place an accelerometer on the top of the shaker platform, use a function generator and amplifier to drive the shaker at sweeping frequency from 2 Hz to 6000 Hz. I also use a polytech laser vibrometer to detect the displacement of the point on the shaker platform close to the location of the accelerometer. Attached are my result. From the acceleration frequency response graph, I see several peaks indicating the "resonance" frequency, according to the vibration theory, the acceleration should be a continuous function of the frequency, it should be a smooth line without any resonance peaks. What is wrong with my measurement? or the shaker is bad? I have make sure the accelerometer is good.

Thanks.

Mike

 

[BrianE22]

I see several peaks indicating the "resonance" frequency, according to the vibration theory, the acceleration should be a continuous function of the frequency, it should be a smooth line without any resonance peaks.

I'm not sure what you mean by that. There will be resonance peaks. Is it the sharpness (looks to be discontinuous) of the peaks that bothers you?

 

[flyeagle]

I think the acceleration frequency response should be like the attached figure. It should be a smooth line, no sharp peaks. This is the result for another same shaker which is good.

 

[GregLocock]

At least one of the two measurements in the first post is complete rubbish. 7mm at 4 kHz is not a believable figure.

Also it is impossible for the displacement to be flat between 1 and 3 kHz and ththe accelerationa laso to be flat between the same frequency limits.

Cheers

Greg Locock


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[BrianE22]

The sharp peaks are likely due to the display resolution. Try zeroing in on the peaks - they'll appear more rounded.