9233: Vibration signal contains dc offset

Hai all,
Am using cRIO 9012 controller and 9233 vibraiton module for acquiring vibration data from vehicle using IEPE accelerometers. Data iam acquiring is not symmetric about zero and the FFT of this acquired data shows a dominent peak (than any other peak) @ .1hz which means that signal has a dc offset. But from the specs 9233 has an ac coupling which means that dc signal should be filetered. Am getting problem in analysis due this behavious. Why is this behaviour? Can anyone help me out in this.
Any quick response will be appreciated.
With best regards,
JK
With regards,
JK
(Certified LabVIEW Developer)
Give Kudos for Good Answers, and Mark it a solution if your problem is solved.

Hi JK,
The DC offset comes from the amplifiers and the ADC.
You shouldn't have any useful data below 5Hz, so you can just ignore any bins that are 5Hz and below. For idle channel noise tests (and others) we ignore any bins that are 20Hz and below.
The DC offset is expected and you should ignore your really low frequency bins. Out of curiosity, why are you worried about the 0.1Hz bin anyway?
Hopefully this helps!!
Aashish M
Applications Engineer
National Instruments
http://www.ni.com/support/

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Solved!
Go to Solution.

Hi CracKatoA.
Take a look at the link bellow:
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mhed wrote:
Hi,
i capture an analog signal (a sine) with labview and i want to extract several informations from the signal like : Amplitude, offset, peak value, frequency, etc.
I almost get what i want, but i can't get the correct value of AC / DC components of my signal.
For example, i receive a signal like this one :
y = 1.25 + 1.25 * sin (2*Pi*3000*t).
I except the following value :
f = 3000 Hz (I got it)
Peak = 2.5 (I got it)
Ampl = 2.5 (I got It)
DC = 1.25 (I got it)
AC = 1.25 and there is the problem. I don't have this value.
Maybe i forgot a vi in my design, or maybe labview can't process this value or maybe i'm do it wrong because i don't exactly talk about AC value.
Look at the terms you reported and compare to your equation. There is a "DC=1.25" and an "Ampl=2.5" in your list. Your equation describes a sine wave with an amplitude of 2.5 units (peak-to-peak) centered at 1.25 units. I believe you are trying to solve for an extra term!
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9233: Vibration signal contains dc offset

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