Real FFT vi - output units?

[Mike]

Is the output units of the Real FFT vi in rms?
So, if my input signal in in volts the output is in Volts rms or if my input
signal is in PSI
my output is in PSI rms?

The help file does not specify, but I think it is in units rms.

Thanks

MIke

[Photon_Dan]

If your time-based signal is unit X, then the real FFT function will give you X rms^2. Use Spectrum Unit Conversion.vi to get you the X peak-to-peak if that's what you want.

You can find that VI from the Function palette at Analyze >> Signal Processing >> Frequency Domain >> Spectrum Unit Conversion.vi (bottom row, second from left usually).

Are you trying to analyze the signal from a dynamic pressure transducer? Perhaps trying for combustion dynamics monitoring? We do that stuff.

Daniel L. Press
PrimeTest Corp.
www.primetest.com

[Mike]

Thanks for the pointer Dan. That makes my results look more like they
should.
I will probably not use the Real FFT vi in my final version. I will use the
Mag-Phase FFT.
But the Real FFT was the easiest one to use to get me started, as I have
only been using
Lab View for a couple of weeks.

I am gathering data from a pressure transducer on the output of a small gear
pump,
looking for small pressure fluctuations and the associated frequecies. I
gather the data
on a standalone Data acq. system, then post process the data as we do not
have a data acq.
system compatible with Lab View yet.

Again, thanks for the help and I may need more......

Have a good weekend,

Mike
"Photon Dan" wrote in message
news:506500000005000000098B0000-1023576873000@exchange.
ni.com...
> If your time-based signal is unit X, then the real FFT function will
> give you X rms^2. Use Spectrum Unit Conversion.vi to get you the X
> peak-to-peak if that's what you want.
>
> You can find that VI from the Function palette at Analyze >> Signal
> Processing >> Frequency Domain >> Spectrum Unit Conversion.vi (bottom
> row, second from left usually).
>
> Are you trying to analyze the signal from a dynamic pressure
> transducer? Perhaps trying for combustion dynamics monitoring? We do
> that stuff.
>
> Daniel L. Press
> PrimeTest Corp.
> www.primetest.com