analyzing signal

[mosquito]

how to change the incoming signal from time domain to frequency domain for ac signal? then how to analyze it to get the frequency of the peak magnitude?tq for the help

[Norbert_B]

The transition from time to frequency domain is the fourier transformation. Usually, we use the fast fourier transformation, short FFT.

The peak search is rather simple since the result of the FFT is an array of frequencies with f0 as first element and each next element is deltaf "higher" (so index 2 is 2*deltaf + f0)

You should do a short search for "FFT" and "Maximum" in the palette (maybe quick drop).

hope this helps,

Norbert

[MarcoMauri]

Compute the FFT of the time domain signal.

There are many VIs you can use to to this, simply search for them in the Labview help.

Once you get the frequency spectrum, in order to find the peaks use for instance the "peak detector" VI (more infos in the Labview Help).

Marco

[mosquito]

do we need to change our signal from analog to digital signal first?

[mosquito]

we are connecting the hardware to the computer using respected VI. from there we straightly connect it FFT VI, but there's an error..they said the error is because of array..how we can fix it?

[Dennis_Knutson]

You should at least attach an image of the block diagram (or the actual VI) since it's impossible to know what you have done.

[mosquito]

ok, i will attach it..once i go back to my university next week..tq

[mosquito]

this is the input we get from our circuit..from the frequency graph, we are required to find the frequency of the 1st and the 2nd peak amplitude of the signal..but how to do it?

[johnsold]

It is hard to do much with a fuzzy picture.  Also, many people on this Forum cannot or will not look at proprietary file formats such as .doc (other than NI files, of course).  Please run your VI to get data like you have shown.  Then Make Current Values Default and save the VI.  Post that VI.

From the time domain graph it looks like your frequency is about 3-4 Hz.  On your frequency graph that data is all lumped together at the far left edge.  From the image it is not possible to tell whether you have enough resolution to separate the low frequencies.

Your question is also not clear: Do you mean the frequencies of the two highest amplitude peaks in the spectrum?  Your DC component will likely be one of them.  Is it intended to exclude that?

Lynn

[mosquito]

actually from the signal, obviously the freq for the highest amplitude is at 0Hz, because it's the frequency of our supply, right? the problem now is i want to know how to detect the frequency of the 2nd highest amplitude from the graph..in other word, how can i find automatically the frequency of the highest y-value (other than at the 0 Hz) so that after detecting, i can use other IV to analyze that frequency..tq 😃