measuring torsional vibration / frequency

[walter-donovan]

Hi all. I hate to ask for peoples' time on this board if I haven't well researched it but.... I have a one shot measurement project that has to be done ASAP and just want a little basic info. I have done a half dozen project in Labview (mostly analog), some digital triggering. I don't know by heart the LV toolbox.

I have to measure backlash, more precisely the variation from perfect steady rotation of a belt driven timing pulley (48 tooth) due to varying torsional load. Equipment id LV 8.5 full dev, bare USB 6211 or 6212 with SCC-2345 (no frequency module),  a laser position sensor capable of over 100 kHz w/0-5v output. I have never tried to reduce analog signals to realtime frequency or period.

This is a one shot test so I am not looking for a pretty interface or automation. I just need to take a sample from the laser and have LV process the semi square wave signal so that I can retrieve period or frequency and fill and array with one revolution. 48 teeth, 5000 RPMs, 100kHz sampling rate will give good enough resolution of ~1200 data points. I can dump the array into a .csv to analyze so I just need to sample and get the period or frequency.

So.... question is - what are the best LV tools in my box to get the period or frequency info out of the raw signal?

[Kira_T]

Hi Walter,

I would suggest using the Signal Processing tools from the functions palette.  From here you will find VIs to perform calculations on the waveform you get out of your DAQ task.  Here is a link a list of functions that perform Waveform Measurements. 

http://zone.ni.com/reference/en-XX/help/371361E-01/lvwave/waveform_measurement_vis/

This would be a good place to start.  Hope this helps.

Regards,

Kira T

[walter-donovan]

Thank Kira. Which one of these tools did you have in mind? I spent time looking at them and tried the only 2 that looked like they gave either period or frequency info - Timing and Transitions.vi & Pulse Measurement.vi. Both seemed to have the same limitation - They would take only one period or frequency measurement per group of samples. I am trying to quantify rotational speed variation through each revolution so I need to keep polling the ferquency or period throughout a revolution. Is there something that does that?

[preston_johnson]

There is a LabVIEW toolkit which converts pulses from tachometers (yuour laser) to speed, and also goes the next step and analyzes variations in the speed to produce a torsional vibration frequency.  This toolkit for LabVIEW is the Sound and Vibration Measurement Suite.  http://sine.ni.com/nips/cds/view/p/lang/en/nid/209061

[walter-donovan]

Thanks. That's a big ticket for one measurement and I'm already past my deadline. I think I'll buy a TC9400 F/V chip for about $4111 less. Unless someone here has got an idea how the Labview I already own can do this.