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Vibration FFT from accelerometer

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Vibration FFT from accelerometer

Postby jmack » Wed Apr 09, 2003 1:58 pm

I am looking at the PICO ADC-212/3 to be used to collect vibration data from our test stand and I really do not know what I need to do this. Anybody that has advice is welcome.

We need to print a spectrum of the vibration from 0 to 80k hz in db or ins/sec and also the over-all level. What do I need to do this?

Can anyone recommend an accelerometer to be used with this system? I would like to get 3 of them for three different locations.

That is the basic requirements and then I few general questions.
Are there any filters available to remove low end and high end vibration?
Where is the vibration data stored before the FFT is used? I was reading that data storage rate to the disk drive is 240Hz and that is too slow if the FFT is done after the data is transfered to the disk. Will that limit the useful range of the FFT?
jmack
 

Postby matthew » Thu Apr 10, 2003 9:18 am

Hi,

The ADC-212/3 should be fine for this if the 12-bit resolution is sufficient. A better unit would be the ADC-216, this has a more accurate clock, and 16-bit resolution.

All of our scopes are two channel, so you won't be able to measure 3 sensors simultaneously ... I can't offer any advice on the sensors since we don't make these but http://www.rswww.com may be able to help.

The data is collected into a buffer at high speed, then downloaded to the PC (much faster than 240Hz), and the FFT is applied. It is not a continuous process, so if you need continuous highspeed data capture, our products will not be suitable.

You can buy analogue high/low pass filters from many electronics vendors, but you'll need to source these yourself.

Best Regards,
Matt Everett

Pico Software Engineer
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Postby jmack » Thu Apr 10, 2003 12:51 pm

Does the software allow FFT spectrum averaging? Our machines do not have discrete frequenices and the amplitudes vary. Without averaging overtime we may not get meaningful results.
jmack
 

Postby matthew » Mon Apr 14, 2003 8:34 am

Yes,

The free PicoScope software does incorporate an FFT averaging mode from Settings|Options|Advanced.

Best Regards,
Matt Everett

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