HRV FFT Spectrum

Hello, Iam trying to perform HRV FFT Spetrcum analysis on filtered ECG Signal, i am facing 1 major problem which is acquiring the RR intervals from the filtered rectified ECG Signal, i have tried to look this up a lot on the internet and tried a lot of things that did not yield to promissing results. Can somebody suggest the most efficient way to extract RR intervals from filtered rectified ECG wave?

Hi Ayman162,
What software are you using? Would it be possible to use arrays to analyze the data? If so, you can use logic combinations to look at the y-values in the array. If we are expecting the peak of the QRS complex to be about 1 mV, we can start using comparison logic when the values exceed .8 mV for example. Then when the y-value (n) is LESS than y-value (n-1), we can store the timestamp associated with the (n-1) value. The next time we get a timestamp from the peak of the QRS complex, we just subtract the first timestamp from it to get the RR interval.
I didn't get a chance to look through this page, but at first glance it seems like it might be helpful, so I thought I'd include it:
http://www.physionet.org/tutorials/hrv/
Jeff Munn
Applications Engineer
National Instruments

Similar Messages

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 .
Thank you for helping.
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?
Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)

Adding a 'minimum hold' option to fft spectrum vi

Hello
I wish to add a 'minimum hold' function to the averaging parameters in
the fft spectrum vis in labview in order to display a continously
updating spectrum displaying the running minimum value across a given
spectrum, but am having some difficulty. I have tracked down the code
in sml averaged fft power spectrum vi where the 'peak hold' option
originates, and can see it is all ready there for me to create a 'sml
min-hold vi' from the 'sml peak-hold vi' and just wire the min output
instead of the max output, but I cannot edit these files, I guess
because they are contained within the _nisml.llb? Any advice would be
greatly appreciated.
Cheers
Ramsey

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.
Thanks
Rob L
NI Applications Engineer
UK & Ireland
It only takes a click to rate this message ;-)

Fft spectrum (mag-phase).vi: dependencies

Dear,
I'm having trouble using FFT Spectrum vi's. When I'm trying to add them to my vi, I get a 'Add to Project and Update Dependencies' error (see attached).
I can use the VI though.
Each time I open the project I keep getting the window to resolve the dependencies. When done, I save the project but the next time I have to start all over again.
Its like the settings aren't saved?
Can this be solved please?
Kind regards,
Ronny Comyn
Belgium
Attachments:
dependencies problem.jpg ‏444 KB

No yellow excalamtion marks.
Screenshots enclosed
kind regards
Ronny
Attachments:
proj_1.jpg ‏465 KB
proj_2.jpg ‏488 KB
proj_7.jpg ‏469 KB

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.
Multiplying the voltage and current waveforms will give you instantaneous power - almost. If you are using a multiplexed A/D converter, then there is a small time delay between channels. That produces a phase shift that will introduce errors in the instantaneous power and other results like power factor. For example sampling two channels at 8 kHz means that each sample on one channel is 12.5 us apart. Consecutive voltage and current samples may be separated by half that much (assuming you are only sampling two channels). The phase shift at 50 Hz from a 6.25 us delay is 0.11 degrees. You will need to decide it that introduces more error than you can tolerate. Faster sampling will reduce that. Using a simultaneous sampling DAQ device (which contains one A/D converter per channel) will eliminate it.
Lynn

SVT 3.1 FFT Spectrum Magnitude VI output is RMS or Peak (db OFF)

Please help with my SVT problem:
1. With db OFF, what magnitude EU value does the SVT 3.1 FFT Spectrum VI output? More to the point, is the EU an rms value or peak value? I thought it was rms but now I'm not sure.
2. When I double integrate acceleration values to get displacement then feed the displacement waveform to this FFT Spectrum VI, I seem to get high displacement values compared to other portable analyzers in our shop. If the output of the FFT Spectrum VI is for example, mils rms (single sided) I have to convert this to peak-to-peak values. So I multiply the each spectrum value by 1.414 (to get peak) then by 2 for peak-to-peak. Is there a more accurate way to get peak-to-peak displacement values from an acceleration waveform?
thanks,
Glen

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.
If you have doubts about the units returned on a specific function I recommend using the Context Help in LabVIEW. As shown on the image below this gives you more information about the function and the variables used/returned by it. You can open Context Help by going to Help>>Context Help in LabVIEW.
Hope this helps. Regards,
Tica T
Applications Engineer
Message Edited by Tica T on 04-04-2006 10:38 AM
Attachments:
units.JPG ‏50 KB
functions.JPG ‏85 KB

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
solution over a limited band. I think SVT stands for Sound and Vibration Toolset.

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).
Attachments:
Averaged_FFT.vi ‏51 KB

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

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.
For example
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
up to Mic 10
Now i want to be able to average these spectrums so that I can regenerate the time series that would be found (or heard) if the listener was to perceive all 10 mics timeseries at the ear without the phase cancellation effects of the time domain.
So I take all 10 mics complex FFTs and I average across every column. I do this by summing all ten mics complex bin values and diving by 10 + 0i.
The result I get is very close to what I would expect in the frequency domain. I would imagine that if i was to take all ten signals with the same time series what is rengenerated in the frequency and time domain would be the same...
However the iFFT returns NaN
There must be a problem with my averaging process - can anyone shed any light?
Thanks
Greg

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.
2. Are there any NaN values in your array of means?
Can you post a small subset of the data (10 x 1000 rather than 10 x 133210) and your VI so we can see what is going on?
Lynn

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).
I am attaching the gaph in attachment 2 from where you can undersatnd what type of resolution and frequency span I want.
Attachments:
fft graph2.JPG ‏39 KB
desired values for scales.JPG ‏35 KB

FFT Spectrum from 2D array

Hello everyone,
I am trying to make the Spectrum analysis from a 2D array. In this case is Amplitude (Y) vs Depth (X). The problem is that the depth (X) doesnt have a constant dt so I cannot create a normal waveform as an input for the Power Spectrum analyzer or Spectral Measurements vi.
This is an example of some of the data that we have:
Depth (x) Amplitude (y)
8390.7
-15.767
8391.2
15.767
8391.7
6.8555
8392.2
-6.8555
8392.7
25.754
8393.2
-25.754
8393.7
2.8505
8394.2
-2.8505
8394.7
-8.574
8395.2
8.574
8395.7
-16.145
8396.2
16.145
8396.7
-0.063
8397.2
0.063
8397.7
3.3945
8398.2
-3.3945
8398.7
7.712
8399.2
-7.712
8399.7
-6.267
Thanks for any help
Solved!
Go to Solution.

I gave you a portion of the signal that always have a constant dt. Sorry ... There is another part of the signal where there are different dt's :
8407.5
-26.08
8408
-15.189
8408.5
15.189
8409
6.5495
8409.5
-6.5495
8410
54.577
8410.5
-54.577
8411.2
-24.185
8411.5
24.185
8412.3
-41.445
8412.5
41.445
8413.4
25.7285
8413.5
-25.7285
8414.1
12.4975
8414.5
-12.4975
8415.2
-16.5155
8416.1
16.5155
8416.6
-24.4

Need help with FFT for Vibration Analysis

Hello all,
I am acquiring data into LabVIEW from an accelerometer. The acceleration (in g's as determined within MAX) time domain graph works fine. However, I wish to do analysis using an FFT spectrum. All my attemps at wiring my time domain acceleration data into various FFT.vi's have resulted in blank graphs, including the sound and vibration module VI's. I am accquiring at 2000Hz. Obviously I am doing something wrong. Can anybody shed some light on how I can get a successful FFT working?
Kind Regards
Adam

I attached an example that works well for me - gens a signal, converts to waveform data type, does FFT
Preston Johnson
Principal Sales Engineer
Condition Monitoring Systems
Vibration Analyst III - www.vibinst.org, www.mobiusinstitute.com
National Instruments
[email protected]
www.ni.com/mcm
www.ni.com/soundandvibration
www.ni.com/biganalogdata
512-683-5444
Attachments:
Generate Signal and SV FFT.vi ‏20 KB
gen sig and fft.JPG ‏32 KB
gen sig and fft.JPG ‏32 KB

Frequency Response Function & FFT & Inverse FFT (problem of unit Volts-RMS)

Hello everyone,
I am currently working on a VI in order to compare two analog signals : the first one corresponds to the output signal (my reference) which is sent by my data acquisition card to a shaker and the second one corresponds to the input signal recorded by an accelerometer fixed on the same shaker. The final goal of the VI is to correct the analog output signal by using the analog input recorded signal in order to have the vibrations on the shaker which corresponds to what we really want.
To summary, I have a problem of unit with the Volts-RMS...
So this is my method for the VI :
First, I have to calculate the Frequency Response Function between the two analog signals (output and input). For it, I use the " Frequency Response Function (Real-Im).vi " which returns the complex values of the FRF in Volts-RMS (but I don't want to use this unit).
Then, I want to calculate the FFT of the analog output signal (my reference). There are two different blocs which can be used : " FFT Spectrum (Real-Im).vi " and " FFT.vi ".
The " FFT Spectrum (Real-Im).vi " returns the FFT complex values of the signal in Volts-RMS and the " FFT.vi " returns the FFT complex values in Volts (or say me if I am wrong, thank you). I really would like to use the second one because of the unit.
Then, I divide the FFT just calculated with the Frequency Response Function calculated just before.
For the end, I calculate the inverse FFT of that with the " Inverse FFT.vi " which use the complex values with the same unit than for the " FFT.vi ".
I don't want to use the Volts-RMS unit because I absolutly want to use the blocs " FFT.vi " and " Inverse FFT.vi ".
The problem is that I don't find a bloc which use the same unit for the Frequency Response Function. The " Frequency Response Function (Real-Im).vi " returns only the complex values in Volts-RMS unit. Maybe it is possible to convert it correctly? Or maybe there is an other bloc which can be used in order to calculate the Frequency Response Function with the same init than for the FFT and Inverse FFT ? Because I can't mix everything for the moment...
Thank you for your help,
Best regards,
Sebastien

Hello Preston,
No, I have not use the Sound and Vibration toolkit. I have only used the signal processing toolkit with the two toolboxes " Waveform measurement " and " Transforms ".
But I think that what I have done for the moment in my VI is correct (I have finished the complete VI). But I am not sure of the units (Volts, Volts-RMS...) and I would like to understand.
I have tried with the Sound and Vibration toolkit for the frequency response function (because you say me that it deals with all the unit conversion) and I can obtain the same results than with the " Frequency Response Function.vi " of the toolbox " Waveform measurement ".
But I would like to understand the units (see my previous post please). For example, for the FFT (the result is a complex), why sometimes it is in Volts, sometimes it is in Volts-RMS ? Is it possible to convert it ? How ?
If you want, I can attach on the forum my VI and that will maybe help you to explain me. Maybe it will help other people interested.
And if someone else can give me other precisions or advices about it, do not hesitate.
Thank you for your help,
Sebastien

How to increase the number of samples in my fft?

Hi,
In my Labview environment I receive sampled data of a sinus function where one period consists of 4096 samples. How can I increase or control the number of samples which the fft spectrum is using for calculating its results?
Best regards
Jonny

Hi,
The sinus signal is generated to have a fixed frequency, but as seen in the figures the fft has a big SNDR. I hope do decrease this with adding the number of samples.
Thanks
Attachments:
power_spec.JPG ‏50 KB
power_spec_block.JPG ‏9 KB

HRV FFT Spectrum

Similar Messages

Maybe you are looking for