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Torsional Vibration Analysis (TVA) - NI Hardware/Software

I have an application were I need to perform a TVA on an engine using two encoders.  One of the encoders is coming in at 720 pulses/rev (360 tooth disk with sync signal) and the other is coming in at 40 pulses per rev (20 tooth disk with 2 missing teeth).  The maximum speed of the engine is 10,000 rpm.  Based on my calculations this puts the required sample frequency at over 120kHz.  The pulses are TTL level.


I am trying to find out if anyone has any recommendations for this application as far as NI hardware and software tools.  Also would like to hear if you have performed this type of analysis before using NI hardware/software.

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Isn't the 120 kHz the frequency you get by the first encoder (720 pulses/rev) ? with about twice the samplerate you would just get the signal if you sample long enougth. But to get torsional vibaration you would need to measure the phase relation of both signals. If you capture long time you migth get e reproduceable phase measurement, but you need it faster to measure the TV ...

I would use counters...

depending on the missing teeth on the second wheel W2 (the missing teeth are not so nice)

-use index to arm the a start tigger with delay according to the next missing tooth of W2.

-use two timers to measure  the duration to up to 18  tooth on W1.

-retrigger on W2

-repeat to get 40 values 

the timer 'jitter' is your torsion...


since the encoder will have individual spacings,



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Thanks, for you input.  Much appreciated!!!

Yes 120 kHz is what I get from the first encoder.  This would be the fastest.


What would you recommend for sample rate to get TV?


Do you have recommendations on NI counter hardware to accomplish this?


What about adding the two teeth back into the W2 encoder.  Would that help?


Also, I like your quote.  So true!

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