Cross power spectrum
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
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
Attachments:
crs.zip 97 KB
Similar Messages
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Hello
I can not figure out how to use "Cross Power Spectral Density" (CPSD)
in Labview. I know that Labview has something about
"Cross Power Spectrum" but I need Cross Power Spectral
Density, because I am going to measure the coherence which
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Thaks for your help.The following example code should be helpful. Please take a look, thanks!
Analyzing Two Input Signals Using the Cross Power Spectrum VI -
How to calcualte Cross power spectral denstiy in Labveiw??
Hi all,
I unable to figure out how to calculate the cross power spectral density(cpsd) in labview ??? I'm able to calculate crosspower by using
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i know that, we can get that through script node function cpsd(x,y) but i shouldn't use that it is my functional requirement.
And one more, Is this right?? psd=power spectrum/ df. where df is frequency resolution.
could any one please help me...
Thanks and regards
GiridharHi girikavali,
does this help you? cross power spectral density and Analyzing Two Input Signals Using the Cross Power Spectrum VI.
Note: The "cross power spectral density" should mean the same as "cross power spectrum", says Wikipedia - CPS/CPSD.
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Cheers, -
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Attachments:
soundgen.vi 15 KBTo start do a search in the examples that came with LV for FFT. This will show you a good cross-section of what LV has to offer in terms of analysis capabilities. The thing to remember is that you can perform this analysis on data directly from a device or post-process data that you read from a datafile. After going through the examples if you have specific questions, we'll be able to give more specific answers...
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Power Spectrum no longer working correctly after upgrading to 8.0.1
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In addtion to Altenbach's comments -
I'd recommend trying another VI function to get the power spectrum for
your signal to see if the behavior is the same. You can find some
examples of VIs using the power spectrum functions using the NI Example
Finder.
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National Instruments -
Signal-to-Noise ratio from Power Spectrum?
Hi,
I have a feeling this is a basic issue but for some reason I'm not getting it. I hope this forum can help.
I have a Power Spectrum (freq on the x-axis and power on the y-axis) and I am trying to determine the signal to noist ratio of the rf signal live.
I am using LV 8.5 and have the spectrum toolkit and am using an RFSA in a PXI chassis.
Any suggestions?
Thanks
- rf curiousHi Rf Curious,
This questions does not have a simple
answer but let me share my thoughts and you can decide what it makes
most sense for your application. For signal to noise ratio (SNR) you
should have ideally the power of the signal and divide it by the power
of the noise. The problem here is that you are looking at both at the
same time (rf live signal). Depending of what type of signal is it, you
can recreate it and substract it from the spectrum (you will need to
recreate the phase and magnitude and delete it from the phase and
magnitude of the spectrum). This is normally done with simple signals
such as a tone.
If you don't have access to the magnitude and
phase of the data, and you only see the spectrum, then you will have to
do things different. You can probably measure the power of the signal
by measuring the power of the band where the signal is located. Then,
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instrument (with same attenuation and RBW settings) and have a rough
estimate. This method should have better results when S >> N. You
can also take the adjacent channel (or further) noise reference.
Finally,
if your signal has a pretty flat spectrum, then you can only take the
difference between the noise and the signal since they both have the
same RBW.
If by now, you have found other methods, feel free to post your ideas here for any other person that come across this problem.
Regards,
Gerardo O.
RF Systems Engineering
National Instruments -
Basic accelerometer-power spectrum readings
Hi all,
I'm new to Labview and am trying to create a simple power spectrum logger. I've had a look at multiple tutorials but am stuck getting to places (most of the tutorials require sound and vibration toolkit, are really old and incompatible with Labview 2011 etc). The program I'm trying to do is:
1) Collect signals from accelerometer (4kS/s)
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3) Save to disk (on board the cRIO)
My setup is:
- cRIO 9014
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- Labview 2011
So far, I've managed to get the signal readings (XYZ axis) and merge them, put them into a 'Collector' block and then output them to the power spectrum block. I've very crudely used a 'Time Delay' block to set the sample rate (which I know is probably not accurate, but I cannot figure out how else to do it). I'm having a problem figuring out how to input the sample rate into the collector, which is why my power spectrum is giving me 0 to 0.5Hz (it's likely assuming the sample rate is 1Hz). I've attached my .vi.
Would someone be able to point me to a tutorial/example/alternative solution? Thank you very much in advance.
Attachments:
accelero.vi 93 KBI think what you want is the CompactRIO vibration data logger. It does not require the S&V measurement suite, though you will find it very useful.
Check this out!
http://zone.ni.com/devzone/cda/epd/p/id/6388
It has a waveform acquisition template for the FPGA. It has a data logging state design.
You can see a Video of it working here
http://www.ni.com/mcm/wind/
Let us know if this helps.
Preston Johnson
Principal Sales Engineer
Condition Monitoring Systems
Vibration Analyst III - www.vibinst.org, www.mobiusinstitute.com
National Instruments
[email protected]
www.ni.com/mcm
www.ni.com/soundandvibration
www.ni.com/biganalogdata
512-683-5444 -
Hi
I would like to save a power spectrum ( about 80000 lines of data) as a file that i can later plot. When i write the cluster (coming out of FFT Powerspewctrum.vi) to an excel (excel works only upt o 56000 or something like that, so i can´t use it anyways) or .txt file using the a combination of open -write -close file i get weird number and letters and not the data i´d like to have. Which data format ( iwould like to make graphs in origin) and vi´s should i use to export the spectrum or is it the best to extract the y-value of the spectrum (magnitude) using the unbundle by name .vi and export it as txt?
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I plan on using this to write to the file from an accelerometer connected to a NI-9234 c-series module through a cDAQ-9178 usb chasssis. So my intention is to use this as a subVI to connect the accelerometer signal from the DAQ Assist of another VI. I am trying to record the spectral data. Attached is the attempt at recreating your code.
Attachments:
Save Power Spectrum.vi 55 KB -
Memory leak with Power Spectrum function
Hi
I have a memory leak on my application. By observing with the "Desktop Execution Trace Toolkit", the Power Spectrum function (from NI_AALPro.lvlib) seems to have two "Reference leak".
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Any idea ?
Thanks...
(See attachments : Desktop Execution Trace + code)
LV8.6.1 + Desktop Execution Trace Toolkit 2009
Same problem with LV2012 + Desktop Execution Trace Toolkit 2012
Attachments:
DesktopExecutionTraceToolkit.png 82 KB
MemoryLeakPowerSpectrum.zip 7 KBHi Mathilde,
Thank you for using NI Discussion Forums!
I reproduce this problem with LV2012 + Desktop Execution Trace Toolkit 2012. I will look further into this.
Are there many calls of this function in your code? Could it be a problem for you?
Thank you.
Regards,
Audrey_P
National Instruments France
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Journées techniques : des fondamentaux aux dernières technologies pour la mesure et le contrôle/comm... -
I am trying to find out what is the equation for the Low Sidelobe Window which is mentioned in the Power Spectrum VI. Hanning second sidelobe is around -32dB of the first. What is that for Low Sidelobe?
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In SPT's implementation, the time interval controls the shift in number of samples. The scales indicate the wavelet coefficients at integer scales 1,2,3,...,"scales" are contained in the output scalogram.
NISH DSP
Medical ultrasound and signal processing -
Need Help related to Power Spectrum of two signal
Hello Sir,
I have two signals of different frequencies but i want to take the FFT power spectrum of both signals at same graph . So for that case i take the FFT power spectrum of both signal indivisualy and after this build the array. so i got the one graph and all the components in same graph. Now
The problem is that in that graph i want to extract the magnitudes at each frequency, but when i extract the information from final graph it will be the " 1D array of Cluster of 3 Elements" so its information is saprate for these two signal. but i want to tale the magnitude at each frequency , how can i got this sir . Please Help me
AgniveshSir it works thanks but there is one new problem is that wahen i am going to extract the magnitude for every frequency it is also works, but my question is that if my frequency is in floating point then how can i extract magnitude for that frequency. i mean i extracted the magnitude for every frequency component starting from 0 to 1...2..3...4.............so on (Frequency ) but if my frwquency id 2.3Hz so how can i do this.i am sending you my VI also
Agnivesh
Attachments:
Analysis HP Compressor test 1.vit 3485 KB -
Power Spectrum Density conversion to Time Series Data
Hi,
This may seem an odd request but is there a way to convert power spectrum density data back to the time series data that generated it in the first place. I have lost the original time series data but still have the PSD and need the time series to do other analysis.
Thanks,
Rhys WilliamsHate to be the bearer of bad news, but there are an infinite number of time series that will generate a given PSD. You lose all phase information upon taking the PSD. For this reason I almost always save time domain data, or at least complex FFT values.
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Read Text row by row, plot them and find the max of its Power spectrum
Hi, everyone,
I have to read data from a text file, plot as a time serie and find the frequency to its max power spectrum. I found a previous post related to my issue so I revised his example a little bit. But once I decide to store the data into an array, the Labview reported:' Error 1 occurred at Scan From String (arg 1)'. Can anyone help me out?
Thanks in Advance!
Gab
Attachments:
ReadXYZmine.vi 18 KBAgain my attachment got missed out.
- Partha
LabVIEW - Wires that catch bugs!
Attachments:
ReadXYZmine_Trim Whitespaces.vi 19 KB -
Switching 2D array for Avg Power Spectrum?
I have a 4 channel 2D array signal which is now indexed so that I can feed 1 channel to the Avg Power Spectrum. It would be much better to have the switching done by radio buttons instead of wired in the Block Diagram. How are the Radio Buttons positioned between a 2D array and the 1D array required by the Avg Power Spectrum?
Regards,
RaymondI answered your question here. Since the radio button control is just a numeric control, replace your hard coded indexing with a front panel one. Here's a picture of what I mean.
Attachments:
array_indexing.jpg 4 KB -
Ok here's the deal.. I acquire data (of type numeric array) from an acuqisition unit (the specifics of it aren't important for the problem) at a known sampling rate and wish to perform a power spectrum on this data. I've used the build waveform function to build a waveform from the 1D array of data with the addition of the dt value (1/Fs) and a timestamp and fed this waveform into the power spectrum vi. The spectrum is then plotted on a waveform chart.
However each time a new data set arrives from the acuqisition unit, the chart is overwritten.I would like to keep the previous data but would prefer not to use shift registers due to the possible size of the array. I thought if the chart's type was a "strip chart" it would hold the data until the buffer is reached but this doesn't seem to be the case.
Another possible issue is with the timestamp but I think I've accounted for that.
Note: The attached vi won't run successfully due to not being connected the the acquisition unit. I was hoping the problem might be clear to someone with more experience using the power spectrum function. I have used it successfully with generic sine waves.
Strokes
Attachments:
Power Spectrum.vi 19 KBStrokes,
you listen to mp3 music from time to time? Maybe, you have configured your application playing those mp3 to display something called "Bars and Waves" (at least, Microsoft calls it like this in Media Player). This display is comparable to an equalizer view.
Your display of the power spectrum analysis is really comparable to this
Does it make sense that the graph does not replace (read: update) instead of "concatenating"?
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.
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