# How to find out if any signal has a noise signal and if so in what range?

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Mehmet Rizelioglu on 12 Dec 2021
Commented: Mehmet Rizelioglu on 14 Dec 2021
Hi guys,
I have an accelerometer signal and how do I know if there is no noise signal in this signal. Also, if there is noise, in what frequency range was it?
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Mehmet Rizelioglu on 12 Dec 2021
Frankly, I did not fully understand.

Matt Gaidica on 12 Dec 2021
Edited: Matt Gaidica on 12 Dec 2021
Mehmet, do you have a recording from the accelerometer at rest and is that the condition which you want to test for 'noise' against? I think you might find some help here: https://stackoverflow.com/questions/67992691/how-to-calculate-95-confidence-level-of-fourier-transform-in-python
If it were me, I might record 1,000 seconds from the accelerometer, split that into 1-second recordings, perform an FFT on each, and create my own confidence interval for each frequency bin (this, of course, depends on your sampling rate). Then you could easily apply your own criteria to determine if there is some extra signal and at which frequencies it exceeds some confidence/alpha/p-value of your choosing.
Mehmet Rizelioglu on 13 Dec 2021
I understand bit because i am new here

Walter Roberson on 12 Dec 2021
I have an accelerometer signal and how do I know if there is no noise signal in this signal.
There is noise in all accelerometer signals, even the very best of them.
You cannot use only an accelerometer for accurate "dead reckoning": you need an Inertial Navigation System (INS) for that, and it takes a fair bit of work to combine information from multiple sensor types in order to get accurate position information. https://en.wikipedia.org/wiki/Inertial_navigation_system#Drift_rate
If you ever see a manufacturer claim that they have "no" noise in their accelerometers, then they are... mistaken.

Image Analyst on 13 Dec 2021
Yes, your accelerometer has noise -- all instruments do.
You can look at the signal spectrum with the device not moving. Presumably this signal is just all noise. Use fft() or pwelch(). However the noise may be different when it's still versus when it's moving. So then do that again with the accelerometer moving in a typical motion that you will use. Compare the two spectra and see what frequency range they are different in. Attach your signals if you need more help.
Mehmet Rizelioglu on 14 Dec 2021
Hi, not moving as 2 seconds, then starts moving. i have sent you my data's FFT and PSD. I would be very grateful if you could take a look at it in your free time.