accessing array elements

[Norbert_B]

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tinamoli wrote:

Hello UliB,

You are the only one ,who understood my question,and solved my problem.[...]

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tinamoli,

UliB answered the question therefore nothing was to say about that anymore. But as Christian, Dennis and i am saying: The background of your question remains complete in the dark. In one post you are saying that you come from biomed and Dennis gave very valuable tips on this. But you keep blocking those tips and asking very obscure questions.

So i suggest that either you'd explain why you want to know this or please listen to us!

I'll explain in a very short way why you will not get the correct results from your approach if your aim is to get the frequency, the amlitude and so on from the signal:

a) You asume that the signal repeats itself 100% identically. But this is not true. So even if you take a non-simulated sine as signal, this will not be the case. There are always errors in your acquistion like samplingerrors and noise Those affect only the amplitude of the signal. The frequency itself will stay the same, but those errors will prevent your algorithm from finding repetitions.

Try your algorithm if you add noise to your signal. I promise that you will have a real hard time to get the correct frequency!

b) Since your signal (ECG) is from a living organism, the signal itself changes all the time and therefore worsen the possiblity that your algorithm will work. So not only the amplitude of all those peaks will change, but the frequency as well.

I promise you that going on asking those questions of yours, you will stumble from one question to the next. You have entered a maze and it is obvious for me that you cannot proceed in there on your own. It is a good thing trying to get a helping hand, so please dont misunderstand me here. But if you ask for help, dont make the mistake to stay in the maze and insist that someone has to guide you all the way through it if some other can take you to a good road to bypass the whole maze!

hope this helps,

Norbert 

[tinamoli]

Message Edited by tinamoli on 10-13-2008 01:39 PM

[tinamoli]

Right Norbert B,

i will discuss to my professor( project supervisor) about this maze!

[tinamoli]

Hello Norbert B,

The biomedical start up kit is not available for me,so can you tell me how to know the period for ECG waveform,or any non_periodic signal with this labview 8.2??

also i would be very happy if somebody suggest me a forum for biomedical engineering?

[Norbert_B]

tinamoli,

Fourier set up a theorem a long time ago. This theorem is nowadays very valuable since it proofed to get the expected results in many, many application.

The theorem states:

All peroidic signals are a sum of sinewaves with different frequency, amplitude and phase.

Fourier didn't only postulated this theorem but created the mathematical basics for solving this. This basics are now used in the Fouriertransformation which i already linked. Some guys (more intelligent than me) modified and optimized that algorithm and build the Fast Fourier Transformation, in short FFT.

FFT is the most common technique to retrieve frequencies from signals.

Regarding the biomedical start up kit: It is simply a toolset using those basics in order to analyze biomed-signals. You can, with appropriate knowledge, program all the features on your own. I am not 100% sure, but i would guess that the toolkit is written completly in LV.

There are many knowledge bases and tutorials on frequency-analysis available.

The most important thing for you to find out about is what are the results you have to look at. If you use ECG signals, there will be many sinewaves included in order to create that signal. But most of those waveforms are not for interest for you. So you have to extract the information out of the timedomain (the ECG) a well as out of the frequencydomain (result of FFT).

hope this helps,

Norbert 

[tinamoli]

Hello UliB,

can you show me how to take the difference(subtract) between each two alternative array elements,example:element1-element2,then element2-element3,,element3-element4,,and so on.

and then comparing these differences to find the minimum difference between which two element?

thanks,

Message Edited by tinamoli on 10-20-2008 03:52 PM

[altenbach]

You can use "rotate array" to shift all element by one position, subtract this array from the unshifted array, then wire to to "array min/max". (You might need to trim the ends, depending on the data)

(You can also use a while loop and a shift register. Have you tried. ;))

[UliB]

Hello tinamoli,

here is an example saved for LV8.0.

I delete the first element from the array, subtract this array from the original array and use 'Array Max & Min' to get the min value and index of the min value. Maybe you want to use the absolut minimum value?

Hope this helps.

Uli

Message Edited by UliB on 10-21-2008 12:49 PM

[tinamoli]

That's it UliB,thanks a lot

May you help me in :

how to search  the array element to find the first maximum value,and knowing the index then continue searching  the array again exactly from the maximum index,to find the index for other desire value,

For example if first maximum Is 0.8 mv with index X ,then from this maximum index I continue searching for 0.5 mv,then again from this 0.5 mv index I search for the next maximum index which can be another 0.8 mv (maximum)also,

As shown below i want to find two successive R amplitude at which index,of course this wave is for one period only and the waveform is continuosly  repeating.

[tinamoli]

UliB,

can you see this vi please,may be I am in right path according to previous message