Pb d'acquisition et d'analyse de signaux

Bonjour,
J'utilise labview afin d'acquérir deux signaux. Lors de l'acquisition, de manière aléatoire, il arrive que des bruits viennent perturber le signal acquis (bruits de + ou - 5V pour un signal variant de -3 à 3V) alors que lorsque je vérifie ces voies sur MAX, les signaux sont clairs. Il s'agit de deux signaux acquis à partir de jauges d'extensiométrie passant par deux ponts d'extensiométrie séparés. Pensez-vous que ce problème provienne de l'acquisition ou du traitement? Faut-il mettre un filtre spécial ou une autre fonctionnalité de LabView?
De plus, j'ai essayé de visualiser ces deux signaux sur une seule courbe et l'outil de traitement (VI-express statisques) ne me permet pas de traiter ces deux signaux de faire une c
omparaison de celles-ci séparemment. En effet, je demande les valeurs maximum et minimum et leur temps respectifs et le vi-express ne me donne les valeurs que pour une seule courbe. Pourriez-vous m'éclairer sur ce sujet? S'agit-il du vi-express qui n'est pas adapté à ces opérations?
D'avance merci
Guillaume Valentin

Similar Messages

Joint time frequency analysis in Signal Express?

Is it possible to do joint time frequency analysis in Signal Express? I didn't see it in the Analysis section, so I'm assuming it's a separate tool that has to be added, if even possible in Signal Express. Help?
Solved!
Go to Solution.

SignalExpress does not natively support joint time frequency analysis. However, check out the Sound and Vibration toolkit which expands upon SignalExpress. It may do what you want.
This account is no longer active. Contact ShadesOfGray for current posts and information.

Problem to read/write and Analyse/Regenerate Signal

hey,
i would like to do a complex platform. i have a RF signal, i would like to save it in a binary File (like TDMS file) and after that, i would like to regenerate it, but i have a problem with that.
My configuration: Labview 8.5 with modulation toolkits, OS Windows XP, PXI-5660 (Analyser) and PXI-5670 (Generator)
Find two VIs attached, please help me
Seb_MDI
France
Attachments:
Save_read_test_dynamique_trigger_IQ.vi ‏87 KB
read_emit_test_dynamique_IQ.vi ‏87 KB

Hello,
You can use the Arbitrary Waveform Generation Mode, in order to generate custom data with your RF signal generator.
You will find an example doing this with a simple file : LabVIEW » Help » Example Finder and look for RFSG Write Signal From File.vi
This will help you do what you want. You will have to retrieve the data from your TDMS file like it is done in the example with binary files.
Have a nice day.
Regards,

Pb d'acquisition et d'analyse de signaux

Bonjour,
J'utilise labview afin d'acquérir deux signaux. Lors de l'acquisition, de manière aléatoire, il arrive que des bruits viennent perturber le signal acquis (bruits de + ou - 5V pour un signal variant de -3 à 3V) alors que lorsque je vérifie ces voies sur MAX, les signaux sont clairs. Il s'agit de deux signaux acquis à partir de jauges d'extensiométrie passant par deux ponts d'extensiométrie séparés. Pensez-vous que ce problème provienne de l'acquisition ou du traitement? Faut-il mettre un filtre spécial ou une autre fonctionnalité de LabView?
De plus, j'ai essayé de visualiser ces deux signaux sur une seule courbe et l'outil de traitement (VI-express statisques) ne me permet pas de traiter ces deux signaux de faire une c
omparaison de celles-ci séparemment. En effet, je demande les valeurs maximum et minimum et leur temps respectifs et le vi-express ne me donne les valeurs que pour une seule courbe. Pourriez-vous m'éclairer sur ce sujet? S'agit-il du vi-express qui n'est pas adapté à ces opérations?
D'avance merci
Guillaume Valentin

En ce qui concerne votre problème de traitement avec le VI Express Statistiques, le résultat obtenu est tout à fait normal car comme le spécifie l'aide de la fonction, elle ne prend en compte que le premier signal et non l'ensemble des courbes. Si vous désirez faire ce traitement sur tous vos signaux, utilisez les fonctions d'indexation de tableaux pour récupérer chaque courbe séparément et faire le traitement pour chaque courbe.
Pour votre problème de bruit, comment connectez vous vos capteurs sur la carte, êtes vous en référencé à la masse, en différentiel. La connexion effectuée correspond elle à celle définie sous MAX?
Le mode différentiel est mieux adapté lorsque vous travaillez dans un environnement bruité, mais il faut voir si vos capteurs le supportent.
De plus, pourriez-vous faire un test sur la fréquence du bruit généré pour savoir s'il s'agit du 50Hz.
vous trouverez en fichier attaché une image expliquant les différents mode de connection.
J'espère que cela vous aidera, n'hésitez pas à me tenir inofrmée des résultats de vos tests.
Attachments:
connections.bmp ‏221 KB

FFT analysis of a spectrometer signal

Hi all,
I am acquiring spectrometer (Ocean optics hardware) signal via USB data acquisition into LabVIEW.
The signal is
Wavelength(nm)        Intensity
xyz                              xyz
xyz                              xyz
xyz                              xyz
xyz                              xyz
The set up is as follows. The light is incedent on the PET film which has a thin coating of dielectric material using Ocean optics spectrometer.
Now i need to analyse this signal to find the thickness of the dielectric material and frequency components using FFT.
Excuse me if i am not clear about anything.
Regards,
KM

Hi ejkaiser,
Sorry i was little bit confused with the data set i posted before. let me make it clear.
The spectral data set (Raw Data) is as shown below.
The thickness data is shown below. I need to increase the resolution of the thickness data. Excuse me if i am not clear about anything.
Raw data from Spectrometer
Wavelength (nm)
Intensity
344.16
1257.45
344.381
1257.45
344.603
1257.45
344.824
1273.84
345.045
1232.88
345.267
1671.14
345.488
1605.61
345.709
1634.28
               continues uptil
1041.76
1693.67
1041.91
1621.99
1042.07
1638.37
1042.23
1716.2
1042.39
1708.01
Output after FFT
Thichness (X-Axis)
150.2n
Amplitude (Y-Axis)
15.0889
300.4n
22.9708
450.7n
11.9293
600.9n
13.9295
751.1n
37.245
901.3n
81.2098
1.052u
122.347
1.202u
111.464
1.352u
48.7365
1.502u
27.3915
1.652u
value continues
19.6806
Regards,
KM

How lab view can be used for signal analysis of hf signals recrded in field

im interested in using labview tool to analyse hf signals in terms of removing noise ,amplipying signal strand identify modulation schemes used

The kind of things you mention are certainly within LV's capabilities. When you say "HF" what frequencies do you mean?
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
Be thinking ahead and mark your dance card for NI Week 2015 now: TS 6139 - Object Oriented First Steps

Signal analysis for DAQ

Hello,
what is the easiest way in performing signal analysis on a signal from a DAQ device?
For example if i can obtain a sine wave signal from a DAQ ,how can i program labview to give me a indication if the signal is correct ie. sine wave, ampltude, frequency, etc etc
with the option of setting the error of eg. 3%
and also if the curve is unorthordox, can you plot points if the ideal signal, to determine and compare it to the signal obtained from the DAQ and say if it is ok ? with the option of error.

Hi Labviewwuser3,
Good afternoon and I hope your well. Thanks for your post.
You have many options to analyses your signal.
The easiest is maybe an express VI called Equal, it allows you test if two waveforms are the same, greater, less and within tolerance (error).
More in depth you could use some of the VIs in the maths>> Signal processing >>Signal Operation such as peak detection. You could then compare the locations of peaks and amplitude.
You could also do this on a point by point basses or on a complete waveform...
Hope this helps to get you started,
Message Edited by Hillman on 12-18-2008 01:31 PM
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help!

How can I perform continuous acquisition of a repetitive waveform?

I want to synchronously acquire a repetitive waveform where there is little or no dead time between cycles. I plan to use an external trigger and scan clock. I need to store each cycle of the waveform as a separate record so I need to know the start and stop sample for each cycle.
I considered putting an N sample acquisition inside a Do While loop, but I can't afford to drop cycles.
I'm considering doing a continuous acquisition and calculating the correct number samples to read from the buffer for each waveform cycle. My concern with this method is that I need to acquire waveforms for a long time (many hours) and I'm concerned about losing synchronization. I've thought that maybe I could acqu
ire say a 1000 cycles and then restart the process, which would minimize dropping cycles and maintain synchronization.
Any suggestions? Am I making this harder than it really is? I probably should say that I'm using a 6052E DAQ sampling at 100ksps.

Hi
I am trying to solve a similar problem at the moment (I have a discussion going in the 'Dynamic Signal Acquisition and Analysis' section) but have not found a completely satisfactory solution so far.
I am acquiring an analogue signal from a rotating machine from which I also have a TTL signal which gives me a once per revolution (OPR) marker. I want to continuously acquire the analogue signal and use the OPR pulsing signal to 'chop up' my continuous analogue signal into a set of data for each rev.
I have used a method similar to the one you have described - I use continuous double-buffered acquisition to acquire the analogue signal and the counter values, with the OPR pulse signal as the counter gate. However, I have been unable to synchronise the s
tart of the signal and counter acquisitions together. I can start the signal acquisition using the OPR signal as a trigger but not the counter. I tried using GPCTR_Change_Parameter() to set the start trigger to external (ND_ENABLED) but this is not permitted with my E Series device (PCI-6111E with DAQ-STC).
Do you know a way round this? And even if I could start my counter acquisition using the OPR signal, how do I ensure that I haven't missed any revs between starting the signal and counter acquisitions (in tests where I use immediate software triggers for the signal then the counter in successive lines of C++ code, my counter is already 2 cycles behind at just 100Hz OPR).

How to acquire analog signal and send a TTL pulse at the same time based on PXI 6123

Hi,
I am using a PXI-6123 data acquisition card, as the picture show in the attachment ,I want to acquire the analog signal of ai0 through reference analog window and at the same time send a TTL signal to trigger my camera. I have tried two methods, one is using the DAQmx Export signal.vi another is using DAQmx connect terminals, but when the data acquisition card acquire the analog signal, the DAQmx Export signal.vi and the DAQmx connect terminals sometime can send an TTL pulse ,sometime can not.
I don’t know why? or some other method that can achieve my arm is appreciated.
Regards
chunlei
Attachments:
method export signal.vi ‏21 KB
method connect terminal.vi ‏36 KB
Send a TTL pulse.JPG ‏288 KB

Hi,
Have things changed over the years?
I need to syncronise a digital output (Modul NI9474) and an analoge input (AI-Modul NI9203) module. I need to measure time intervals from a flank in signal A to a flank in signal B. I would like accuracies of the order of 1 ms. Currently, the signals are not synchronised, with errors of the order of 2 times the block length (block size x sample rate), sometimes much higher. The best I got so far was a block size of around 20 with a sample rate of 1 kHz.
If I use the master and slave settings on the RTSL settings, my program doesn't run properly.
If I use digital signals for input and output, I can syncronise them with RTSL settings and everything is good, but I can't always do that.
Also, if I do anything in the GUI (such as scrollowing something or going to another window), my output gets screwed up properly.
1. What can be done to synchronise AI with DO?
2. Is there something that can be done to avoid messing up the output when something happens in the user interface? (I know that I am messing up the outputs as they make some valves switch and that is loud).
Thanks in advance!

Continuous Trigger to sync up on burst of signal

LabVIEW 2009PXI-5122 using NI-Scope 3.4.1 How do I set up the scope to continuously trigger and sync up to a signal burst in the back ground. The signal is serial data that is transmitted in bursts with dead time in between each burst of data.This dead time is less than 20% of the duty cycle of the data. With the correct hold off and triggering settings I can lock on and sync up with the data stream,
But it take a number of iterations before it syncs up (8 to 10 iterations) But once there it is fairly solid. I would like to set up the scope to start triggering on the signal in the background.Give it time to syncThen go through all the UUT tests checking for the correct data without having to wait for the scope to re-sync each time I want to read At present I read in an array of records each time and throw away the first 7 records.
At about the 8th or 9th record the scope is in sync with the signal. It just seems that there should be an simpler way. I have tried different setup including Start and Fetch, but each time I have to read in 8 or 9 records before I get one that is sync. How do I set up the scope to continuously trigger and capture data even if I do not read in the data?Then when I need the data, make a call to get the most resent and complete record as I need it? Omar
Omar

Hello Omar,
Can you give me more details about your application? Are you doing analog or digital acquisition? What kind of signal are you trying to acquire? How does the signal that you are trying to sync to look? Can you attach any screenshots? What is the relationship between the acquired signal and the signal you are tring to sync to?
As far as your question about setting up the scope to continusously trigger and capture data even if you do not read your data, unfortunately you cannot do this on NI Scope. You must fetch all your samples from your onboard memory. You cannot just skip records to be fetched. Therefore you cannot get the most recent record only.
Regards,
Efrain G.
National Instruments
Visit http://www.ni.com/gettingstarted/ for step-by-step help in setting up your system.

Continuous data acquisition using NiDAQmx with a start and a stop trigger

I'm sorry if this has been answered many times before, I can't quite seem to find the answer I'm looking for.
I am using LabWindows CVI version 7 and NiDAQmx with a PCI6023E.
I wish to acquire data continuously using an external clock as a timebase - I am happy with this.
I wish the acquisition to start when an external signal (say on PFI7) goes high. I am also happy with this.
What I also need is for the acquisition to stop when the signal on PFI7 goes low, or possibly when a signal on say PFI8 goes high. I'm not too concerned about which approach to use.
How do I stop the acquisition with an external signal?
Thanks in advance,
Crispie

I don't have CVI installed, but I've attached screen shots of a LabVIEW program that I believe accomplishes what you are trying to do. Translating it to the C API should be straight forward. I'll try to explain what the program is doing since it's using some of the more advanced features of the driver. Also, the DAQ device you are using doesn't support a true "stop" trigger so I'm using a reference trigger to get as close to the desired functionality as possible.
First, the program configures a finite acquisition that uses both a start trigger and a reference trigger. The acquisition is using an external sample clock and will acquire 4 samples (2 pre-trigger samples and 2 post-trigger samples). Four may seem like an odd number here, but it allows us to emulate the functionality of a stop trigger as close as possible. Given this configuration, you must acquire at least 2 samples before the "stop" trigger is recognized, and you must acquire 2 more samples after the "stop" trigger is recognized. Hopefully this restriction is acceptable. You can always discard the last two data points after the stop trigger if they're not of interest, but you're stuck always acquiring at least two points between when the start and stop triggers are recognized.
The program also overrides the default buffer size and read position. By default, the DAQmx driver will pick a buffer size exactly big enough to fit the pre-trigger and post-trigger data (4 samples in this case) and will begin reading data from the start of the pre-trigger data. Explicitly allocating a larger buffer will allow your acquisition to execute without receiving buffer overflow errors, and changing the default read position will allow you to read all of the data between the start and stop triggers as it is acquired and not just the pre-trigger and post-trigger data.
Finally, the while loop takes care of reading the data. In this case, the loop continues to read data until the task is done and there are no longer samples available for reading from the buffer. The number of samples read per iteration is the lesser of the user specified amount or the number of samples available for reading from the buffer.
I hope this helps. Good luck.
Attachments:
Stop_Trigger1.JPG ‏40 KB
Stop_Trigger2.JPG ‏43 KB

Sound level options for voice analysis

I have two questions.
I am analysing voice signals using GRAAS microphone, NI9234, cDAQ 9178 & labview 2011. I am trying to produce a two dimensional graph of the signal with SPL (DB)(y-axis) versus frequency (x-axis). I noticed that the SVT sound level.vi from the sound & vibration toolkit outputs into 4 different values;
1. exponential averaging sound level (dB),
2. Leq sound level (dB),
3. running leq sound level (dB), and
4. peak sound level (dB).
Which of this four should I use.
Is it right that I should use linear weightage for human voice analysis?
Thanks in advance

If you've put the sound level to max & still not so comprehensible audio, it could be a hardware fault. A long shot, this haps to my friend check the small hole for the speaker if there is grit/dirt blocking it.
Knowledge not shared is knowledge wasted!
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How to use wavelet analysis in labview 8

Dear everybody
how can i use wavelet analysis in labview 8
thanks in advance

Hey khairy,
There's quite a bit of information available at ni.com about wavelet analysis and how to perform this in LabVIEW. By just doing a quick search, I came up with the following links:
NI LabVIEW Advanced Signal Processing Toolkit:
http://sine.ni.com/nips/cds/view/p/lang/en/nid/1395
Advanced Signal Processing Toolkit Demo:
http://zone.ni.com/devzone/cda/epd/p/id/4765
KnowledgeBase Articles:
Custom Wavelet Analysis Using Signal Processing Toolkit in LabVIEW
http://digital.ni.com/public.nsf/allkb/11ABBF34A0D8E9BB86256E55005CA69D?OpenDocument
How Do I Use the Continuous Wavelet Transform to Produce a Scalogram?
http://digital.ni.com/public.nsf/allkb/79EABCEBCA56F65686256F340062C4D7?OpenDocument
Good Luck!!
Brian B
Field Sales Engineer
Tennessee/Southern Kentucky
National Instruments

Change form of output signal without initializing new process of output signal

Hello!
How to change form of output signal produced on the output channel without initializing new process of output signal?
Thanks
Message Edited by _Pavel_ on 10-28-2009 05:21 PM
Solved!
Go to Solution.

I'm working with LabView 8.5.1.
I have periodic TTL impulse with constant frequency – signal to start , which I'm used to start data acquisition (PCI-6251)and generation signal (PCI-6221).
When TTL signal a detection, necessary generation some analog signal (PCI-6221) and acquisition other analog signal (PCI-6251). Then wait following TTL signal.
At this moment I write the part of the program which is responsible for data acquisition. Function retriggering (In examples C:\ProgramFiles\National Instruments\LabVIEW8.5\examples\DAQmx\Synchronization\Multi-Function.llb\Multi-Function-CtrRetrigg Pulse Train Generation for AI Sample Clock.vi) is used. This function necessary,because we start data acquisition each time on arrival TTL impulse, andrepeated creation of the virtual channel of data acquisition with the newtrigger spend a lot of time.
The problem consists in the following. Generation of the data from other card should occur on the same impulse TTL as for the data acquisition card and then generation zero value.
How I can realize it? I planned to change the form of an impulse of generation when detected TTL an impulse, without reinitialize process.

Two signals at two waveform graphs

Hello Everyone!
I got some problems with my software for data acquisition.
I got two signals and I have to show two signals at two different Waveform Graph.
How to seperate signals?
Solved!
Go to Solution.
Attachments:
separate.png ‏37 KB
spearate.vi ‏23 KB

I read DAQmx help and what I know is that Each row corresponds to a channel in the task. Each column corresponds to a sample from each channel.
I really don't know how to wire Index Array... Can you explain it to me, please?
Look at the attachment, is it ok?
Attachments:
explain.png ‏8 KB

Pb d'acquisition et d'analyse de signaux

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