cross power spectrum

[chanakya]

hi

I'm trying to obtain cross power spectrum of two time domain data (signal conditioned accelerometer o/p's) using 'cross power spectrum.vi'. The vi o/p one being the 'cross power xy spectrum mag' & the other being the 'cross power xy spectrum phase'. I need to plot the frequency with 'cross power xy spectrum phase' or in other words, I need the corresponding frequency value for the calculated 'cross power xy spectrum phase'. This is required for the calculation of phase delay (phase diff / corresponding frequency) and inturn calculate phase velocity


Regards
Ajit

[ElSmitho]

Salutations Ajit,

So, you want to calculate the "cross power xy spectrum phase" and also obtain the frequencies... Well, go to "Analyze" --> "Signal Processing" -->

"Frequency Domain" --> "Cross power spectrum.vi"

This VI should enable you to find the spectrum mag and phase, along with the "df" values. From these df values, you could always build a waveform ("Waveform" --> "Build Waveform"), using whatever you pleased along with df. Then plot this (or get a chart) on a waveform plot, giving you the frequencies and other necessary information.

I do not believe this is in the base package of labview, i'm not sure what package it is in.

I hope this is what you desire.

Sincerely,
ElSmitho

[chanakya]

Hi EISmitho

thanks for the suggestion, accordingly I've incorporated the vi you had suggested. The result obtained from the changes made above contained the frequency values also. But I was bit secpticle about the result as the tabulated frequency was just like a serial no. (1,2,3,...)Is it just a coincidence or have I gone wrong anywhere??Would u pls go through it once and respond to me.

thaks for the help

regards
Ajit

[ElSmitho]

Salutations,

After you get your cross power xy spectrum phase and magnitude, you pull out df and then take the inverse of it. I forsee no legit reason for taking the inverse, just plug that "df" value from the function straight into the dt value for putting the waveform back together.

Also, you don't need a t=zero spot, if you don't want it there. Just reshape the function or click on one of the build waveform spots and change it to what you desire. Hopefully, if you make that modification all will work well.

Have fun now and good luck,
ElSmitho