NI-4461+Signal Analysis

[G_BHASKAR]

Hi,
We have a NI-4461 Dynamic Signal Analysis card.I need to plot a Freq Spectrum & Bode Plot(Gain Vs Freq & phase Vs Freq).I am able to acquire data using DAQmx functions,but the DAQmx library does not support Signal  Analysis functions such as FFT,gain and phase plotting.I would like to know if a DSA library is available for this card and how do I download it and use it with the card?
Thanks in Advance
G.Bhaskar

[preston_johnson]

The Sound and Vibration Measurement Suite provides a vast selection of sound and vibration related signal processing, including frequency response.

https://www.ni.com/en-us/shop/product/labview-sound-and-vibration-toolkit.html

There are many signal processing functions available for LabVIEW

https://www.ni.com/en/shop/labview/analysis-and-signal-processing-with-labview.html

And if you are using traditional programming languages, take a look at LabWindows CVI, Measurement Studio, and the Advanced Signal Processing tools

https://www.ni.com/en/shop/electronic-test-instrumentation/programming-environments-for-electronic-t...

https://www.ni.com/en/shop/electronic-test-instrumentation/application-software-for-electronic-test-...

[G_BHASKAR]

Thanks for the info.I understand that LabView modules are available for analysis.But I am interested in libraries(independent of labview) which can be called from traditional programming environments like Visual Basic or VisualC++ .

G Bhaskar

[PBear]

Hi Bhaskar,

The DAQmx library is a tool to aquire data and therefore doesn't contain any analysis tools. It's a very robust driver for hardware communication but as the name applies, it's meant soley for data aqcuisition. Our Sound and Vibration Toolkit is extremely powerul and is exclusive to LabVIEW. You could create a wrapper DLL and make calls to it in C on a computer with LabVIEW. Also, if you have DAQmx installed, you have a data logging tool called Signal Express which can aquire and analyze your data, including FFT. If neither of these are options, you could do a search for libraries containing FFT code.

[G_BHASKAR]

Hi Patrick/All,

Neiher Signal Express nor Labview is a option for me.So I decided to do it in code.I could implement FFT.Next on my agenda is Bode plot consisting of magnitude plot and phase plot of Transfer function(Vo/Vi).I am using the following logic.Pl let me know if this is the correct way of plotting the magitude and phase of the transfer function.??

Vi[ ] --input sample array
Vo[ ] -- output sample array

Vo/Vi[ ]  -- Sample array by dividing each output sample by corresponding input sample

X[ ]=FFT(Vo/Vi[ ])          results in array X[ ] with each index with complex values (x+iy)

Amplitude [ ] =square root of x*x +y*y   of each sample.
Phase [ ] =tan inverse of y/x of each sample

The  amplitude is the maximum value of Amplitude[ ] array (at index z).
The phase is the value in Phase[ ] array at index z. --Is this the way of calculating phase??

I plot the magnitude and phase to get a bode plot.

Any other way of plotting Bode plot??

Thanks in Advance
Bhaskar

[PBear]

Hi Bhaskar,

There's a difference between studying a signal's frequency response and a signals frequency spectrum. For example if you are interested in the response of Vo/Vi as the frequency changes, you would use a Bode plot. A Bode plot is the amplitude vs. frequency or the phase vs. frequency. Usually frequency is logarithmically scaled and the two plots are stacked so you can see their relationship to each other. Phase will change with frequency as well as the amplitude. This is useful in studying transfer functions and how circuits respond to different stimuli.

If you are interested in the spectrum of frequencies that are contained in a signal, you would use an FFT. The highest amplitude would correlate to the fundamental frequency of your signal. This is not the same as phase. If you take an FFT, you will be specifying the frequency resolution (which may not be apparent but your parameters and array length, amongst other things, will set your resolution). So if you're resolution is 10Hz and you're FFT(Vo) = [.2, .2, 51, .2, .4, .3], your fundamental frequency would be 30Hz. Any other peaks above the noise floor will represent harmonics or other tones in your signal. A musical chord, for example, could contain 3 tones but many harmonics.

Please take a look at these documents
Using Fast Fourier Transforms and Power Spectra in LabVIEW

https://www.ni.com/en/shop/labview/using-fast-fourier-transforms-and-power-spectra-in-labview.html

An Overview of Frequency-Domain Measurements
https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YGJ7CAO&l=en-US

[G_BHASKAR]

Hi,
I am going through the tutorial at the links provided.It should give me a better idea.I need infomation on the  following NI product.

Dynamic Signal Analyser -software Product ID 500733D-00  

The above product provides for signal analysis using NI cards.

Is it available with the NI-4461 package?

Or is it sold seperately?

Thanks
Bhaskar

[PBear]

Hi Bhaskar,

That piece of software is a driver for our 445x line of DSA boards. These boards have been phased out as our 446x, 447x, and 449x line are superior. They used to do some processing on chip and thus they had their own driver. Since your board is not from this line, the driver will not work with your card. Instead of using a DSP on-chip, we now empower customers with the Sound and Vibration toolkit for LabVIEW to make custom analysis. For traditional programming languages, we provide great documentation of the hardware tool's functionality so that the user can successfully control it and then use the data acquired in whichever way they choose on their end.

If you are looking for an end-user solution, I would recommend searching google for pre-built libraries to analyze your data and display it.

[PBear]

Message Edited by Patrick_B on 04-11-2008 10:55 AM

[G_BHASKAR]

Thanks for the info.

Bhaskar