FFT Power Spectrum VI in Runtime Engine

Hi,
I am trying to deploy a couple of EXEs on a colleague's PC (of VIs I have written).
He has successfuly installed the runtime engine.
One of the EXEs works fine. However, the other produces a number of error messages concerning the FFT Power Spectrum VI.
Why would this be? Do I need to install any additional drivers in order for this to work?
Cheers,
Dan
Dan
CLD

Dear Dan,
I have just tried this myself, and can not see any problems.
I have also searched National Instruments' internal database, and can not find any previous issues with this particular vi.
Could you provide us with more information regarding the errors you have encounterred, and maybe some steps to allow us to replicate the issue.
Also try rebuilding the exe.
Lastly, if you have not done so already, please try distributing the "Data" folder which is created with the .exe to the target machine (it will contain a lvanlys.dll).
Best wishes,
Rich R
Applications Engineer
National Instruments UK & Ireland

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FFT Power spectrum

It appears that the project I'm working on will end up teaching me a lot about labview because the project is complicated. Using labview, I am spinning two objects at two different speeds, which makes up the signal. One object is being spun at 1200rpms and the other at 2400rpms. This should yield a spike at 20Hz and one at 40Hz. I have a spectrum analyzer which is giving me the results I expect, but I can't seem to get it with labview. I tried using FFT and then taking the real portion of the signal and graphing it, which didn't work. I then tried the power spectrum, which also didn't work. I need some help/suggestions. Any and all are appreciated.
Thanks,
JB

JB,
To help you, we need some help. Specifically, some specifics about your application.
How are you acquiring the signals from your spinning objects? What is your sampling rate? Are the signals sinusoidal, pulses from an encoder, something else?
What did not work? Did you not get any spectrum, was the frequency wrong, was the amplitude wrong, was the resolution poor?
If you post your VI with some typical data saved as default (because we do not have your spinning objects), someone will probably be able to help you.
Lynn

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
Agnivesh

Sir 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

Optimizing Power Spectrum Performance

I'm continuously acquiring data from two channels on a PXIe-5122 at a rate of 50 MS/s (100 MS/s total). I would like to compute the power spectral density of each channel while acquiring the data. I'm currently using the FFT Power Spectrum and PSD VI. I benchmarked the performance of the FFT Power Spectrum and PSD VI on its own and was processing at a rate of about 3 MS/s per channel.
Is there a more efficient VI should I should be using to calculate the PSD?
Is calculating the PSD at these rates even feasible? If not, any suggestions for alternatives? (Would an LV FPGA be an option?)
Thanks!
geoff
Geoffrey Schmit
Fermi National Accelerator Laborary

Hello Geoff,
This is Andrew Brown, an Applications Engineer from National Instruments. The FFT Power Spectrum and PSD VI you mentioned is the recommended method of determining the PSD of data channels. Calculating the PSD given your sampling rates (100 MS/s) would definitely be much faster using the LabVIEW process. However, I was unable to find a specific benchmark.
Some additional resources on using LabVIEW FPGA are located at NI LabVIEW FPGA and in the LabVIEW FPGA Help for FFT. Please let me know if you have related questions on this issue. Thanks, and have a great day!
Regards,
Andrew Brown
Applications Engineer
National Instruments

Windowing and Power Spectrum

Hi,
I have a simple .vi that is attempting to calculate the total PSD over a 500Hz bandwidth. My question pertains to the Windowing function and
what affect it has on the power calculation. I have much on windowing etc. in the NI's help but cannot seem to arrive at the value I am simulating to. I have including my .VI and the associated input file. (this file represents Pulse Densisty Modulated data output from an ADC)
thanks for any help
Attachments:
PSD of PDM.zip ‏127 KB

You may want to try "FFT Power Spectrum and PSD.vi". it takes care of the compensation for the window effect automatically.
Be careful that "Amplitude" compensation is used for Power Spectrum, and "Energy" compensation for PSD. The difference is a scaling factor of 1.5 for Hanning window.
Attachments:
psd.vi ‏20 KB

Power Spectrum peak calculator

Hi,
I am using the "fft power spectrum.vi" to calculate an FFT on a wave and the output of that is some bundled wire called power spectrum. I was wondering is there an easy way to take this output and find and display all the various peaks in the power spectrum? Thanks.
Intern NSWCCD Carderock.

Yes, I did try that, but the problem is I don't understand the inputs required for it as it requires
"X" a set of points, but when you run the power spectrum you get a bundled wire with various parts and I'm not
sure which of these to wire into the peak detector as everything I have tried has given me wierd values. Thanks for
any help.
Intern NSWCCD Carderock.

Keeping Power Spectrum Peaks on a Graph

Hello,
I am trying to read in a signal which varies in frequency as time progresses. I am taking this function and running a real time power spectrum (FFT Power Spectrum.vi) on it. As time goes the peaks move around according to teh frequency which is coming in. What I want to do is to keep the old peaks on the graph as the new peaks come in. So for example if I had a signal which was at 50 htz then 75 htz, at the end of the run I want to see both peaks on my grpah. Is this possible? Thanks.
Intern NSWCCD Carderock.

If you use the Spectral Measurements Express VI, you can configure it to do peak hold. In the configuration screen, turn averaging on, click on the Peak Hold radio button, and set the averaging number to 1. Then all your peaks will be displayed as they come and go. See attached vi. If you want to see how the express vi does it, you can convert the express vi to a normal vi and then look into the block diagram. I believe one of the functions has a peak hold input.
- tbob
Inventor of the WORM Global
Attachments:
SpectralMeasure.vi ‏98 KB

What is the difference between power spectrum and PSD?

Hi all,
I input a time domain signal to the FFT power spectrum VI and FFT PSD VI seperately, and got two outputs in frequency domain with similar shapes but different magnitudes.
I refer to some signal and system textbook, and find PSD(w)=1/pi*Power Specrum or equivalently PSD(f)=2* Power Specrum.But as I observed from the LabVIEW outputs, this relation is not correct. I input a 1KHz sin wave with amplitude=1, Fs=512KHz, #s=2048 , the PS peak is 0.5 and the PSD peak is around 0.013.
So I wondered what's the real formula LabVIEW is using to calculate PSD?
Sunny

PSD is related to spectrum resolution, thus related to sample rate.
df= Sample rate/ #samples
I think they follow this relationship:
Amplitude FFT power spectrum = Amplitude PSD * df * 1.5

LabVIEW Runtime Engine 2010 NI_AALPro Error

Hi All,
I have an problem with the executable version of my LabVIEW program. I just created an LabVIEW program in LabVIEW Professional 2010 version to acquire some FFT spectrums so it also use some function palettes of Sound and Vibrations toolkit like Power Spectrum, Peak Search, Power in Band etc.
Then I just created an executable version of the program to run on a different system (Tools>>Build Executable Verion(EXE)). But when I tried to run the executable verion on a different system is showed some errors. I am attaching a printscreen of all errors showed.
So, the executable version of the program is working fine in the develoment system but showed some errors when we try to run it on a different system. We have already installed the LabVIEW runtime engine 2010 as well in the second system.
My one more question is when we build an executable version of a LabVIEW program then it should run on all PC without any other software (Runtime engine) because it got an extension of .exe
so is there any chance or way to build a totally standalone executable version of the program without using any runtime engine as well.
Thanks
Attachments:
error.JPG ‏28 KB
dll & lvlib.JPG ‏41 KB

Hi PSBRRR,
It seems like you didn't include all the dependencies of your VI or project to your build specification. Can you send a screenshot of the Source Files Setting page of the Application Properties dialog box ? You have to add all the VIs and DLLs that are used in the Sound & Vibration toolkit and any others you are using to your executable file or support directory.
For the last question : no you can't. Since LabVIEW 2010, the Run-Time Engine is like the "Java Virtual Machine". The compiled code inside your EXE is interpreted by the "LabVIEW Virtual Machine" included in the LabVIEW Run-Time Engine. That's why it requires the Run-Time Engine to be executed or at least the development environment (previous versions of LabVIEW didn't use this principle but it was also required to have the Run-Time Engine installed).
Regards,
Da Helmut

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

SMT Power Spectrum to IQ Data

I have a 20 MHz IF Signal.
I used SMT Basic Zoom Power Spectrum to zoom in
and capture 5 MHz of that Spectrum.
Can I get back IQ data corresponding to this Zoomed 5 MHz Spectrum.
I tried using IFFT to get back IQ data from the Spectrum,
but the results are not correct
Which VI should I use to convert Power Spectrum to IQ Data. ?

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 no longer working correctly after upgrading to 8.0.1

Recently, I installed Labview 8.0.1 to correct a problem I was experiencing in 8.0. The installation resolved my problem, but now the Power Spectrum no longer gives the correct result. My program has not changed other than the update. I checked my circuit and everything is functioning properly. Before changing to 8.0.1 the power spectrum peaked at 40Hz and 80Hz, which was correct, and now it peaks at 0Hz and 10Hz. On top of everything, the peaks are much higher than they should be. I expect peaks with a max of 2.5millivolts and now they are 1volt. I don't understand what is going on. Nothing changed, but the software version. Can someone please help me?

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.
You can go to LabVIEW's Example Finder by going to Help >> Find Examples.
Then search for FFT. There should be some results that include FFT and
Power Spectrum Units.vi, Power Spectrum Measurement.vi, Basic Spectral Measurements.vi, and Spectrum Measurements.vi. Try opening and
running these examples to see if the VIs are returning the proper
results.
Mark Walters
Application Engineer
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 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
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,
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

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?
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

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 Williams

Hate 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.

FFT Power Spectrum VI in Runtime Engine

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