Frequency separation without any filters

[shjukheter]

Hello,

             I tried many ways with TDMS signal and with spectrum also but I did not achieve good results. This is my lost hope to finish it. I have a spectrum with highest frequency component at 8kHz and I have full noise after 500Hz which always not constant at particular frequency. The noise varies from 500Hz to KHz. I would like to do it in two ways.

First way is I would like to put a threshold on amplitude(Vrms^2) after 500Hz until KHz but I don't want to use any filter for this.

Second way is I would separate the frequency band after 500Hz to smaller bands and look for the amplitude levels in each band.

Please give me some hints how can I do this in labview  after FFT.

[johnsold]

The output of the FFT is an array. Each element of the array is a complex value representing the contents of one frequency bin.  The spacing of the bins is df.  The value of df is defined in the detailed help for the FFT.  So to do what you want, you need to calculate df, then determine which array elements are in the frequency bands you want, and apply the thresholds to each.  Read the help and try it.

Lynn

[shjukheter]

I did not understand much about df in Labview help. Can you clear me or give some other link which tells about df.

[johnsold]

Do you understand dt? dt represents the difference in time between two adjacent samples in the output of the A/D converter (Analog Input device). In an analogous way df represents the difference in frequency between adjacent elements in the spectrum array.  df is also called the frequency resolution and is defined as df = fs/N where fs is the sampling frequency and N is the number of samples.  The detailed help file for the FFT VI has a table showing the frequency of every element in the output array.

Lynn

[Coq_Rouge]

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@johnsold wrote:

Do you understand dt? dt represents the difference in time between two adjacent samples in the output of the A/D converter (Analog Input device). In an analogous way df represents the difference in frequency between adjacent elements in the spectrum array.  df is also called the frequency resolution and is defined as df = fs/N where fs is the sampling frequency and N is the number of samples.  The detailed help file for the FFT VI has a table showing the frequency of every element in the output array.

Lynn

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http://zone.ni.com/devzone/cda/tut/p/id/4278

http://zone.ni.com/devzone/cda/tut/p/id/4541

I have already given young shjukheter these links and also tried my best to help. But shjukheter seems to just be interested in some sort of magic Express VI doing all the job.

@shjukheter Labview is a programming environment. You are supposed to do some programming with it in order to do the tasks you want done

[shjukheter]

Here I have two images which having noise and no noise. I would like to write a condition that will indicate the noise presence or not. So, How can I exactly find those noise peaks between the my frequency bins to intimate about noise. And also the amplitude is varying. Is there any Vi for this noise detection.

[shjukheter]

Hello,

            I use "TSA periodogram VI" in my FFT convertion and I got the spectrum as well. In the resulted spectrum, I have noisy frequency peaks after 400Hz. I would like to do a search in my program to see if there exist any peaks after 400Hz but so far I could not able do it my own. I am getting three components from "TSA periodogram VI" that F0, df and magnitude of the peak. How can i do a search if there is any peaks after 400Hz. Please give me some ideas. I have no idea how to do it?

[johnsold]

shjukheter,

Both Coq Rouge and I have given you several suggestions.  Have you tried to do any of these things?

If you want help about a specific issue, please do these things:

1. Try it yourself.

2. Post your VI with some data saved as default values (because we do not have your equipment to generate data).

3. Insert comments on the FP or BD of the VI you post indicating what does not work, what you expect the result to be, and any other information which might be useful to us in helping you.

4. Follow the advice you are given.

Lynn

[shjukheter]

I try to do myself and at the same time I could not fix my problem. Please help me.

I have three noise frequency peaks after 400Hz and these peaks will not stay constantly in my graph due to my connected device stroke mechanism. Whenever it touches other part these peaks will appear in frequency spectrum. I just need to write a piece of code, that will say about these peaks after 400Hz whether they exist or not. Sometimes, I need to check these amplitude levels also. 

AS far as, I just got three cluster array data after FFT which contains these data but I don't have much knowledge to make it work as I described. I attached my code in labview 2009 version.

 Please help me.

[johnsold]

I do not have the TSA Periodogram.vi and there is no data in the Waveform graph in the Sound Input loop.

Lynn