Signal Conditioning

cancel
Showing results for 
Search instead for 
Did you mean: 

Octave analysis Hz /dB to Amplitude /Hz

Hello,

i have uff file with data from accelerometr. I want to do octave analysis on that data. Is is possible to have for every Hz listed in octave max value of that Hz. I don't know what to do with this task. I have Sound and Vibration addon.
Below is screen from my program. This is for X axis.one.png

0 Kudos
Message 1 of 4
(2,651 Views)

Hi,
I have stuck with my program.. I have uff file with vibration data. In this file I have data in m/s^2(t) units. And i want to do a 1/3 octave analize on it, so I would like to have on x axis from 0,5 Hz to 100 Hz and on y axis value in m/s^2. How can i do it, with setting proper reference value from my recorder. So in other words I don't want to have dB/Hz but( m/s^2)/Hz.

0 Kudos
Message 2 of 4
(2,629 Views)

Dear TWatroba,

 

unfortunately it is not possible to set the bandwidth to 1 Hz for the Octave Analysis Express VI, for conceptual reasons, since being an "octave" analysis, it divides the frequency domain in a logarithmic way. The available options are 1 Octave; 1/3 Octave; 1/6 Octave; 1/12 Octave or 1/24 Octave

 

http://zone.ni.com/reference/en-XX/help/372416J-01/sndvibtk/octave/

 

In general, if you set the bandwidth to 1/N Octave, then two consecutive bins will have the frequency ratio of Nth root of 2. That's the mathematical reason, that one cannot set the bandwidth to any constant value.

 

Some background for the Octave Analysis might also help you succeed:

https://www.castlegroup.co.uk/guidance/octave-bands/

 

If you need to have the 1 Hz bandwidth, I propose, you use FFT-based functions like the

Window FFT PtByPt.vi:

 

http://www.ni.com/white-paper/4278/en/

 

Best Regards,

NI Applications Engineer

 

 

0 Kudos
Message 3 of 4
(2,538 Views)

Dear Twatroba,

 

first of all I propose to scale up your signal frequency with a factor of 100 by dividing dt parameter in the input waveform by 100, so the lowest frequency will be shifted from 0.5 Hz to 50 Hz, the highest will be shifted from 100 Hz to 10 kHz, so both will be in the range of 20 Hz to 20 kHz. 

 

Use the SVT Third-octave Analysis VI with the following parameters:

low band=50 Hz

high band=10000 Hz

dB On=FALSE so you get a linear output: "band power [dB EU] returns the power associated with each 1/n octave band expressed in decibels rms, if dB On is TRUE and EU^2 rms if dB On is FALSE."

 

http://zone.ni.com/reference/en-XX/help/372416G-01/sndvibtk/iec_third_octave_analysis/

 

After getting the octave spectrum as the output, scale back the nominal frequencies to their real values, i.e. back between 0.5 Hz and 100 Hz thru dividing the nominal "frequencies [Hz]" by 100.

 

Best regards,

NI Applications Engineering

 

 

 

 

 

low band=0.5 

 

http://zone.ni.com/reference/en-XX/help/372416G-01/sndvibtk/iec_third_octave_analysis/

0 Kudos
Message 4 of 4
(2,536 Views)