Power Spectrum with RFSA

Hi all,
I have some question about fetching power spectrum with RFSA drivers.
when i set span and resolution bandwidth as 100M and 1M respective in ni5660 Configure for Spectrum,and use ni5660 Read Averaged Power Spectrum to fetch the power spectrum,does averaged power spectrum output the 100M signal once?
if so,how can i draw the spectrum in Waveform Chart as RFSA demo show us?RFSA demo did use Waveform Chart to draw spectrum,did't it?
Thanks
Liu Yuan

Hello Liu Yuan,
If you take a look at ni5660 Power in Band example in the LabView Example Finder ( Help -> Find Examples ), you will notice it uses a Waveform Graph. The Read Averaged Power Spectrum vi is contained within a while loop which means that it will continuously output the averaged power spectrum. If you want to use the RFSA drivers, I suggest looking at the RFSA Getting Started Spectrum example in the example finder. This example only reads the spectrum once, but you could put a while loop around the read vi to get continuous spectrum output. If you have any more questions feel free to post back.
Regards,
Benjamin Cook

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Memory leak with Power Spectrum function

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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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Attachments:
DesktopExecutionTraceToolkit.png ‏82 KB
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Hi 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
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Find the rest of the peaks and identify them. Why the peaks are where they are?
Attachments:
soundgen.vi ‏15 KB

To 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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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 curious

Hi 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
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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
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you can terminate your input and measure the power of the noise of the
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

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
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Finder.
You can go to LabVIEW's Example Finder by going to Help >> Find Examples.
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Application Engineer
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)
2) Generate power spectrum
3) Save to disk (on board the cRIO)
My setup is:
- cRIO 9014
- NI 9234
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Attachments:
accelero.vi ‏93 KB

I 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

Save Power spectrum

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?
Thanks for any help

I believe this is also something i can use for my application, however, when trying to recreate the code in LabVIEW 2011 SP1, the connections between the For Loop and the Close File return an error that the data types are different.The Path wire returns that the source is 1-D array of byte stream file reference with the sink being byte stream file reference. The Error wire returns that the source is 1-D array of cluster of 3 elements with the sink being a cluster of 3 elements. How would i go about fixing this?
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Attachments:
Save Power Spectrum.vi ‏55 KB

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Attachments:
array_indexing.jpg ‏4 KB

Power Spectrum

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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 KB

Strokes,
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.

Power spectrum not enough memory

I have a binary file that I want to plot the power spectrum of. The thing is.. the .bin file is about 100MB. When I run the attached .vi, it says out of memory. However, I could open the .bin file and plot it with amplitude versus time. Is there a problem with my setup or something I don't know about? Thanks for your time~
Jud~
Attachments:
Powerspectrum.vi ‏25 KB

Hi Jud,
why do you attach a BMP renamed to JPG? Please attach real JPGs or (even better because of lossless compression) use PNG format! There's a reason why BMPs aren't allowed as attachment...
I attached your pic converted to PNG. Do you spot the difference?
Message Edited by GerdW on 08-02-2008 03:40 PM
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome
Attachments:
Error3.png ‏13 KB

Power Spectrum VI Performance

I am looking to accelerate the performance of the Power Spectrum and
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not huge, when doing 3000 of these analyses in a shot, it gets large,
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speed it up. For example, the nubmers i am sending it are fairly
small Single Precision Floats, would it work better with larger
numbers?...
Thanks for all your thoughts in advance.
Eugene

Hi
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"Qod natura non dat, Salmantica non praestat"

Number of cycles using power spectrum for getting frequency

Hi,
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Thanks,
Jennifer

Sorry for the vague first post. The software was already written for the device and I am just trying to understand a few things in order to make some changes.
I am measuring the speed of a turning rotor using the square wave signal generated from a pattern on the turning rotor. I need to know the frequency of the square wave in order to determine the speed of the rotor. The pulse pattern is used in power spectrum and estimate frequency icons (appears to be similar to an example program for spectrum analyzer). The speed of the rotor is variable until it reaches steady state which can take minutes or hours. Speeds are not too high (Freq 1-100Hz). Right now the measurement is set up to sample a given number of points at a given scan rate. This means that the data most likely does not end exactly as a pulse cycle ends but somewhere in the middle of a cycle.
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In the future I will work with completing pulse width measurements which most likely would be the fastest I can complete a transient measurement although my data will have a bit more fluctuations. That's due to each pulse not being exactly the same width.
Hope that gives you a better idea what's going on here.

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I'm streaming data to disk in one loop, however once this finishes I'd like to read the data into power spectrum vi/Octave analysis vi in another loop. The data from the read vi is a string and power spectrum vi needs 1d waveform. Does anyone have experience with this process?

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Taking your data as text is very inefficient. What you really want to do is read the data as binary, use that for your analysis, and use something like the Write to Spreadsheet File.vi to save text data to disk.
This account is no longer active. Contact ShadesOfGray for current posts and information.

WAV power spectrum

I am conducting a sound measurement test using a IEPE microphone and the NI USB 9233. I used the SVXMPL_WAV Recorder (DAQmx).vi to record a Wav file of the sound and then the SVXMPL.WAV Power Spectrum.vi to produce a power spectrum of the wave file. I had a concern that scaling was occurring because the spectrum seemed louder than expected. I read in another thread that no scaling occurs in the vi. Next I used SVMPL_FFT Subset (DAQmx).vi to produce a power spectrum over the same frequency range (20 to 20,000 Hz). In general, the two method agree well except that the peaks in the spectrum are at lower frequencies for the WAV Power spectrum vi than that obtained for the SVMPL_FFT vi. I was wondering if any one could please explain why this is occurring?
Regards,
Bill

Hello Bill!
Thanks for your posts back and the information. So what I have done is I ran approx 1 KHz signal through a series of different programs to see if I could reproduce anything you were seeing. I also used the program you posted as well. However when I run the WAV Recorder (DAQmx) vi and then put that wave file into the WAV Power SPectrum I see the signal at about 1KHz like I expect. Then I aslo use your program to see if I can get the same results with the same function generated signal. I always se my signal in the same matter and the frequency components line up accordingly. See the pictures attached below. Thanks for posting your code and it seems like I am unable to reproduce what you are seeing. Did you make any changes to the VI's in your code? If you could perhaps post the wav files that you are producing to see what I can make of them? Take a look at the screen shots that I was able to produce.
Cheers!
Corby_B
http://www.ni.com/support
Attachments:
Power Spectral Density.jpg ‏225 KB
WAV Power Spec.jpg ‏202 KB
Power Spectrum.jpg ‏142 KB

Zoom power spectrum

Hola a todos, durante el desarrollo de un programa para analisis de vibraciones con un acelerometro triaxial, he encontrado que "zoom power spectrum" funciona normalmente hasta que ha mostrado un nº determinado de espectros, momento en el cual se borra el último espectro y empieza de nuevo a mostrar una nueva serie de espectro adquiridos y haciendo medias si tiene activado está opción.
He provado vi de ejemplo con la misma frecuencia y nº de samples y mismo equipo y no lo hace. ¿a que se puede deber este comportamiento anomalo de este subvi
Gracias

Hi Walban,
I would like to ask for clarification about what you are
looking to do. I understand that you have an inverse FFT, but can you expand on
the definition of ‘different distributions’ ? I am puzzled by how we can have
different data, but the same spectrum. Lastly, what version of LabVIEW are you
using? Are you using the Spectral Measurement Toolkit (SMT)? This knowledgebase: How Do I Use the FFT and Inverse
FFT VIs in LabVIEW? (http://digital.ni.com/public.nsf/allkb/549BCD6B247012F686256E00002509E5?OpenDocument)
may help with using the FFT and Inverse FFT functions in LabVIEW.
David L.
Systems Engineering
National Instruments

Power Spectrum with RFSA

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