Third octave decomposition

Hi!
I’m working about third octave decomposition with a vibration signal.
I’m using the sound and vibration toolkit.
The sample frequency of my signal is 2400 Hz.
I use the vi “1/n octave IEC decomposition” and I would like to know if I can selected the frequency range “1 to 400 Hz” in third octave decomposition? I think the results are strange in a low frequency (1 to 4 Hz)
In fact, for example, the BW of the first 1/3 octave is less of 0.3 Hz!!!!
So it’s possible to begin the third octave decomposition at 1 Hz?
Thanks for your help.
Bastien

thank...
But I would like to analyse a short signal (5 to 10 second) in the frequency range [1Hz to 400Hz].
When you begin the third octave analyse at 1 Hz you must to have a vibration signal with 17.24 s minimal length in time.
this minimum time is say in the user manual of the toolkit "sound and vibration":
Filter Settling Time :
When starting or resetting the filtering operation of the fractional-octave
filters, a certain time is required before the measurements are valid.
This time is called the settling time and is related to the bandwidth of any
particular filter. The lowest frequency band has the smallest bandwidth and
defines the settling time required before you can consider the complete
fractional-octave measurement valid. In the Sound and Vibration Toolkit,.......
settling time is defined as five divided by the bandwidth of the filter used
for the lowest frequency band.
..........The filter settled indicator returns TRUE as soon as all the filters are settled.
When you begin analyse at 1 Hz, the first BW is 0.29. So, 5/0.29 = 17.24 second.
My vibrations signals are too short (5 to 10 second) and I can't have more long because this signals are due to train course and it’s very fast.
I don’t know how to catch information in a low frequency (1 Hz) with a short signal.
Thank for your help
bastien

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Third octave operations with "sound and vibration toolkit"

Hi!
I’m working about third octave decomposition with a vibration signal.
I’m using the sound and vibration toolkit.
The sample frequency of my signal is 2400 Hz.
And I’m working with a 1 second vibration signal (so 2400 points).
Fs = 2400
N = 2400
I need to understand the different and successive operations that the “SVT Fractional-octave Analysis [IEC].vi”VI do.
In fact, I think that my frequency resolution (df = Fe/N=1Hz) is too low.
Do you have a solution?
Maybe I could turn into my 1 sec signal in 10 sec signal with 10 recopies and assemblage of my previous signal?
N’ = 10N so df = Fe/10N = 0.1Hz.
Thanks for your help.
Bastien of paris

Hello,
The first thing you have to do is to read the Chapter 7 of the user manual of the Sound and Vibration Toolset.
You can find it in : program -> National Instruments -> LabVIEW Sound and Vibration Toolset -> User Manual
This chapter discusses fractional-octave analysis, including fractional-octave analysis theory, averaging modes supported by the
Octave Analysis VIs, settling time, and ANSI and IEC standards.
regards,
Marc L.
NIF

The specs for the NI model 4552 DSA card realtime octave addon are listed as max 10KHz band for one-third octave on 4 chan

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Hello Greg,
I cannot say that I have seen a similar problem. Which version of LabVIEW are you using? Which Sound and Vibration option have you installed?
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Attachments:
Power spectra and third octave.zip ‏1225 KB

Hi again,
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How to make third-octave analysis program?

"I want to make a program which can do Third-Octave Analysis. But I haven't any DAQ device of NI company. I use a DAQ device of Nicolet company. That device can tranfer the acquired data as a file to a computer, and then I can use a software to transform the data into ASCII format. The DAQ device hasn't an anti-alias filter. How can I make the program with LabView? My version of LabView is 5.1."

The task that you are inquiring about could become quite complicated. for
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I would recommend that we take this off of the news group and work direct.
I can be reached @ [email protected]
remove no_spam_ for real address
Mike
"stewart342" wrote in message
news:[email protected]..
> The DAQ device of nicolet is called 'vision'. What I mean is how can I
> make a VI to get the analysis result from the data acquired. Because I
> am not good at LabView and signal
processing thoery, I hope you can
> give me a brief example. Though the device provides a filter, the
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I'm studying vibration analysis, and I need to use an already measured data (acceleration in g/ time in seconds) to compare with the vibration criteria curves (picture below).
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http://zone.ni.com/reference/en-XX/help/372416H-01/TOC27.htm
http://zone.ni.com/reference/en-XX/help/372416F-01/TOC20.htm
http://sine.ni.com/nips/cds/view/p/lang/pt/nid/209056
http://sine.ni.com/nips/cds/view/p/lang/pt/nid/209061
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SVT question

I need to measure the following.
I need the to measure the impact sound of a ball
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Seth B.
Staff Test Engineer | National Instruments
Certified LabVIEW Developer
Certified TestStand Developer
“Engineers like to solve problems. If there are no problems handily available, they will create their own problems.”- Scott Adams

Third octave decomposition

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