speed calculation

[ziasaga]

Hi,

Can anybody let me know, why I am getting constant speed from my VI calculations?

I am using 60 pulse/rev encoder disk for a ramp up speed calculations? Where I am making mistakes?

Regards, Niaz

[A_Person]

You're pulling one value out of the speed profile.  What are you getting at the speed output of the Analog Tacho Processing function?

[ziasaga]

Alex,From Analog tacho processing, I am getting many values of speed that sounds okay for only single speed operation. I am trying to collect 5 sec of data for vibration and speed at 5E-5 time interval. I noticed the saved data file for the relevant column has a delta_X of 0.001 for speed and all the other columns including vibration have delta_x of 5E-5 that includes 100000 data. The relevant column of speed I am getting total of 4988 items at 0.001 second intervals gives about 5 seconds worth of data.If you need anything more please let me know. /Niaz

[preston_johnson]

your speed chart is a recreation of your pulse waveform added to the frequency in hz of rotation.  Is this what you are looking for?  Do you want to know speed over time in RPM? are you looking for changes in Speed that might indication torsional vibration?  Are you looking for the angular position of the shaft for each analog acceleration value?

I am not sure what you want your graphic to show.  The speed VI calculates a speed for every pulse from your encoder.  Since your incoder pulses occur at 0.001 (1Khz) that is the number of speed measurements that are made. 

I look forward to your reply.

[ziasaga]

Hi Preston,

I am looking for speed that might indicate torsional vibration?

However, is the any way to change encoder pulses data from 0.001 (1KHz) to 5E-5 (20KHz) for all time, vibration, encoder and speed data?

Thank you, Niaz

[preston_johnson]

Thanks for the clarification regarding the torsional vibration.  In our current release of the Sound and Vibration Measurement Suite, we have Torsional Vibration analysis which uses a multi-pulse per revolution encoder. 

See these links

http://zone.ni.com/reference/en-XX/help/372416B-01/svtconcepts/perform_tv/

http://zone.ni.com/reference/en-XX/help/372416B-01/svtconcepts/use_tv_vis/

These VIs, will perform the interpolation of speed between tach pulses.  Again, the tachometer VI can only determine speed at the presence of a tach pulse.  The way to upsample the speed measurement is to perform an interpolation (spline or cubic) using the speed array and the timestamp array as the Y and X respectively.  

http://zone.ni.com/reference/en-XX/help/371361E-01/gmath/interpolate_1d/

You provide the xi array (with delta-x what yuo need) to get the yi array - and you can rebuild your waveform.  This upsampling is done as needed in the torsional VIs listed above. 

Preston