One third octave alaysis

Hello everybody.
First, I'm sorry for my bad english. Hope everybody understands!
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).
Note that the VC curves axis are Vrms (um/s) X 1/3 octave band Frequency (Hz). Well, I am able to do some integration of my raw data and get the values in velocity X time.
If I use a FFT, I can go to frequency domain. But I don´t know how to express my data using this 1/3 octave band.
I would appreciate a lot if someone could help me!
Thanks in advance!
Henrique

Hello Henrique,
To have a function to do 1/3 Octave analisys direct you need have installed LabVIEW Sound and Vibration Toolkit or Sound and Vibration Measurement Suite.
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
The following link have an example using Sound and Vibration Toolkit functions, but only open if you have this toolkit installed.
https://decibel.ni.com/content/docs/DOC-2085
Best regards,
Abel Souza
Engenheiro de Aplicações
National Instruments Brasil

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There is a thorough explanation of the algorithms and details of the ANSI S1.11-1986 specification to which the toolkit is built around in the reference manual for the Signal Processing Toolkit. Here is a link to it:
http://www.ni.com/pdf/manuals/322142a.pdf
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I would like to analyze steady state, low frequency (0.1Hz to 80Hz) data that has been aquire over several minutes of acquisition at a rate not exceeding 1000Hz. I am using the Third Octave Filtering Tools in the Signal Processing Toolkit, but it is unclear to me that if I just change the sample rate input into the Third Octave Filtering.vi if that will give me the octave bands that correspond to the ranges that I am interested in. Is the any other way to calculate this? For example, if I wanted to find the band power of an individual octave band, say band 0, which has a center frequency of 1Hz, how would I do that?

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Attachments:
Power spectra and third octave.zip ‏1225 KB

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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
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Octave Analysis VIs, settling time, and ANSI and IEC standards.
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QoS - realtime traffic must be less than one-third of link bandwidth capacity

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"misunderstanding" - yes and no
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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.
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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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One third octave alaysis

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