FFT Spectrum (Mag-Phase) unit

Hi,
I used the VI "FFT Spectrum (Mag-Phase) " for 1 Chanfor 1 channel with input data in V.
The magnitude seems to be in volts-rms (Vrms).
Is it possible to have the result of the magnitude in V?
I have seen different topics about that, but no clearly reponse.
Regards
Julien
link to LabVIEW help
http://zone.ni.com/reference/en-XX/help/371361D-01/lvwave/fft_spectrum_mag_phase/

Hi Massif,
Please Read the following KB - What is the definition of root mean square (RMS) voltage?
Here it mentions how you can convert the Vrms value to a V peak value.
I have attached a small VI which you can use to do this conversion.
Enjoy.
Message Edited by Kabul on 06-10-2008 01:09 PM
CLA | LabVIEW 7.1... 2013
www.renishaw.com
Attachments:
VRms to Vpeak1.vi ‏13 KB

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How can i create an indicator to read the RMS value of my FFT using FFT Spectrum (Mag-Phase).vi

Hai to all,
how can i create an indicator to read the RMS value of my FFT using FFT Spectrum (Mag-Phase).vi.
as u can see in my block diagram(attached), i can use statistic to read the RMS value for the data but i cant's use it on the FFT Spectrum (mag-Phase).vi .
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Attachments:
block diagram.jpg ‏48 KB

hafizzuddin wrote:
thank you for the opinions, for now i am not using any express Vi..
In the long run you will benefit from this. Anyway is your problem solved, or do you need more help?
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Dear,
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FFT Spectrum

Hello Everyone,
I am using the FFT Spectrum (Mag-Phase).vi
But whatever avering parameters I use, I always get the same Magnitude Spectrum. I also wonder if I am using the VI in the correct way. I included an example.
Can anybody help me on this please?
Attachments:
SpectrumAnalyzer.vi ‏104 KB

There are two problems in the way your are using the VI. First, the re-start averaging is set to "True" which mean you actually re-start your averaging every time. Next, to average correctly you need to place the VI in a loop (Typically a "For" loop if you are doing linear averaging or a "While" loop for exponential averaging). The VI automatically reset (restarts) it self the first time it is called. Then you can activate the restart boolean when you want to restart the avergaging. I have made a simple VI that shows how it work (see attachement).
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Averaged_FFT.vi ‏51 KB

Svt frequency response (mag-phase).vi

Hello people
I want to find out the peaks from the specrum which get from magnitude output of svt frequency response (mag-phase).vi.
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Dear Lisa,
Are you still here for supporting.
I have installed Sound and Vibration Suite 2011 (SV) to use with LabVIEW Professional 2009 SP1. I have a concerns.
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Normalization of FFT Spectrum

Dear Sir
I take FFT of my real time data that I collect from current probe. I successfully get the FFT spectrum. But my supervisor ask me to normalize the harmonic component present at 25 Hz in the FFT spectrum with fundamental component. Can you please guide me how I should do this task.
Also what is normalization and what are its benefits.
The frequency of fundamental component is 50 Hz.
Your attention and consideration will be highly appreciated.
Kind Regards
Urfee
Solved!
Go to Solution.
Attachments:
LabVIEW 6281-50.vi ‏61 KB

The problem is to know what to use as a reference for the normalization. The image below shows an expanded view of the Instantaneous Current Spectrum with the display style set to show the actual data points. I also moved the frequency indicator wired to the Tone Measurements VI into the image. The frequency as detected is not exactly 50 Hz. Note that the data points in the spectrum are not symmetrical about 50 Hz. This is another indication that the sampling is not perfectly synchronous. The result is that the spectrum contains 11 points fro 49 to 51 Hz which are within 60 dB of the highest point. If you want to normaize to the fundamental, you need to determine the total energy in the fundamental component. That probably includes the data points in that 2 Hz range or maybe slightly more.
Although you stated that you are sampling at 25 kHz, the latest VI you posted shows 8 kHz sampling.
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SVT 3.1 FFT Spectrum Magnitude VI output is RMS or Peak (db OFF)

Please help with my SVT problem:
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Hi Glen,
There are several FFT-based VIs in LabVIEW and the output units of each function is different.
The following table will give you a better idea of what each function does. In your case you might be better off using the FFT VI that comes with the Signal Processing toolkit since you are looking for Volts output instead of the Vrms given by the FFT Spectrum functions.
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Message Edited by Tica T on 04-04-2006 10:38 AM
Attachments:
units.JPG ‏50 KB
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Adding a 'minimum hold' option to fft spectrum vi

Hello
I wish to add a 'minimum hold' function to the averaging parameters in
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Hi ramsey,
I have been trying to find the VI's that you mentioneed but don't seem to be able tofind them in my pallettes. I believe they may be from the modulation toolkit in LV 7.1? Is this the setup that you have? Please let me know as there have been some significant changes with the analysis VI's since that revision.
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What is the difference between SMT zoom FFT, FFT spectrum, SVT FFT spectrum, complex FFT vi, real FFT vi

what is the difference between SMT zoom FFT, FFT spectrum, SVT FFT spectrum, complex FFT vi, real FFT vi in the labview functions palette. I am getting different spectrums on performing the above mentioned ffts on the same time domain data

Complex FFT takes a complex input array and gives a complex output array. Real FFT assumes the input data is real valued only, ie imaginary parts are zero. It can be computed quicker than the complex FFT so if data is real it is better to use this. There is a Power Spectrum vi that computes normalised power of the complex output of the FFT for a real input sequence(sum of squares of real and imaginary parts). Auto Power spectrum gives a single sided output ie positive frequencies only. This is normalised as well. Just check the help on the vis for the normalisation factor. The Zoom FFT isn't in the professional edition of LV. I know zoom FFT comes with the S&V toolkit. It allows one to measure the spectrum of a signal with improved frequency re
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FFT(mag phase) and sample count

I am using the FFT(mag and Phase) VI in version 6.1. When the sample count sent to the fft vi is increased the magnitudes decrease. What is causing this? Does the VI divide by the sample count?
In advance, thank you!

The resolution of FFT depends on the sampling rate as well as the number of samples used to compute FFT (Fs/N). When you reduce the number of samples, the resolution of FFT comes down. This means that the peak that you detected prevously might have gone undetected.
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Finding the mean of a series of complex numbes to generate an avergage FFT spectrum

Hi All
I have a a 2d array of complex numbers. In fact I have a 10 x 133210 array that represents the complex result of a series of ffts taken from the time series of 10 mics.
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Frequency ::::::                 1Hz 2 Hz 3Hz   4Hz 5Hz      ad infinitum(!)
Amplitude for Mic 1             2+2i    2+2i   2+2i 7+2i 2+2i
Amplitude for Mic 2             3+2i    5+2i   2+2i 2+2i 2+2i
Amplitude for Mic 3             4+2i    2+2i   2+2i 8+2i 2+2i
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Greg,
1. The phase effects due to the spacing of the microphones is already in the data. Unless you have a point source, it will be very difficult to sort out which components came from where.
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How to enhance frequency resolution of fft spectrum on x-axis

Dear Sir
I get the frequency spectrum of my real time signal. Frequency span that I want to analyze is 0~500hz. I get that span by setting the sampling rate. But the frequency resolution coming on graph is of 100hz (as shown in attachment). My requirement is to have frequency resolution of 10hz with same frequency span. Please guide me how can I achieve this.
I shall be thankful to you
Kind Regards
Muhammad Irfan
Student
UTP Malaysia
0060149087570
Solved!
Go to Solution.
Attachments:
fft graph1.JPG ‏40 KB

I set the dt value to 0.002. For this I set sampling rate 2000hz and no.of samples 1000000. In this way I achieve frequency span of 250hz. But resolution is still 100hz (as shown in attach 1). My question is how can I set resolution to 10hz? I increase the number of samples but from doing this only the frequency span changes and resolution remain same as 100hz. Resolution become 10hz only when I set total frequency span to 50 hz (but My frequency span of intrest is 0~500hz or 0~250hz not below thos).
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Attachments:
fft graph2.JPG ‏39 KB
desired values for scales.JPG ‏35 KB

What are the units for the power spectrum output? (units in)^2/Hz?

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FFT Spectrum (Mag-Phase​) unit

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