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Waterfall plot acquired in real time doesn't match when it is read offline.

Dear fellow LabVIEW experts,

 

 

I'm in need of help regarding the waterfall plot in LabVIEW. I acquired vibration signals of a CNC router during idling. The accelerometer was attached to the tool spindle in proximity to the rotating tool. Using a LabVIEW program (LV 2010),  I saved my data (using write to spreasheet function) and I also had a waterfall plot showing the vibration spectrum built up as I was collecting the data. I used the Print Screen function on the keyboard to copy the waterfall plot (collected during real time data acquisition) and pasted it in a Word document.  Then, I had another LabVIEW program that was able to read back all the data that I've saved including a waterfall plot that was used to reproduce the vibration spectrum that I've collected. After I read back my data (offline), I compared the vibration spectra between the real time and offline. The vibration spectrum that is collected during real time is supposed to match with the vibration spectrum that is reproduced when reading back the same data.

 

My problem is this, when I changed the location of the accelerometer or the vibration sensor to a new location (a bit far up and away from the rotating tool), the real time and offline vibration spectra didn't match in that the offline one showed some additional frequencies or peaks that weren''t there when I was collecting it in real time. Does anyone know why this happens?...Is it something to do with the buffer?

 

I've tried my best to explain and I hope someone out there is able to explain this situation.

 

Really appreciate any helps.

 

Thanks.

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Can you post you VIs or at least a screenshot of your block diagrams (the one that acquires and save the data and the one that read the file)


We have two ears and one mouth so that we can listen twice as much as we speak.

Epictetus

Antoine Chalons

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TiTou is right some screen shots would be helpful,

 

But these are good references too: http://zone.ni.com/devzone/cda/epd/p/id/5607   http://zone.ni.com/devzone/cda/epd/p/id/1425   http://zone.ni.com/devzone/cda/epd/p/id/5523 🙂

Sam S
Applications Engineer
National Instruments
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