Convert a rpm waveform to digital/analog tach signal. Sound & Vibration

[ProgrammerTN]

Hello,

my question is: How to convert  a rpm waveform to digital/analog tach signal for use with SV application?
Or is it possible to modify the SV - VIs for the use of a rpm waveform or a speed signal?

Thanks a lot for coming answers.

Thomas Nuding

[Jochen]

Is a rpm waveform an analog waveform that is scaled to revolutions per minute instead of Hz? In this case FFTs and so on should simply work as expected. You only will need to take the scaling into account when interpreting the results. Maybe it would be simpler to do the scaling before passing the data to the analysis functions as this would make it easier to avoid errors when parametrizing the vis.

Please provide more details for the case that I didn't understand your question correctly. Are you using the Sound & Vibration Toolkit?

Best regards,

Jochen Klier
National Instruments Germany

[Jochen]

I just thought a bit more about your question. An rpm waveform seems to be a frequency domain waveform so only frequency domain functions will work properly.

[preston_johnson]

Typically an RPM waveform is the analog view of a tachometer, such as a proximity probe over a key or keyway, or an index pulse from an electric motor.  In most rotor dynamics applications, the phase of the tachometer waveform is compared to the phase of other waveforms, such as vibration, to determine the angular position of the shaft when the other waveform occurs. 

The sound and vibration tools have a function for calculating RPM from an analog tachometer waveform.  The order analysis toolset go further to add a counter as an tachometer input.  The OAT tools also allow for selection of rising edge or falling edge and voltage level for the "trigger".  A time instance is recorded when the edge occurs.  This time instance is used for phase measurements and for resampling the other waveforms into the angular domain, ie. 360 measurements per revolution.