## Accelerometer data post processing

## Accelerometer data post processing

(OP)

Hi,

I would like to extract out of acceleration measuring data a chart, which consists acceleration value, its existance length in seconds and the occuring frequency. I think it is called interval average acceleration versus time chart.

The acceleration data is basicly noise filtered values of acceleration in g-s, measured with 512Hz frequency.

Signal processing is new field for me. Is FFT time domain is the right track where to continue?

PS. I am a mechanical engineer, thats-why its unknown field for me.

Is there a simple solution in MATLAB or Excel for that?

Best Regards,

Henrik

I would like to extract out of acceleration measuring data a chart, which consists acceleration value, its existance length in seconds and the occuring frequency. I think it is called interval average acceleration versus time chart.

The acceleration data is basicly noise filtered values of acceleration in g-s, measured with 512Hz frequency.

Signal processing is new field for me. Is FFT time domain is the right track where to continue?

PS. I am a mechanical engineer, thats-why its unknown field for me.

Is there a simple solution in MATLAB or Excel for that?

Best Regards,

Henrik

## RE: Accelerometer data post processing

Matlab or Scilab (free) have many frequency analysis and plotting functions. Excel is also a possible way to go, but you need a little more than the standard package.

Do not understand "FFT time domain". Looks like you are mixing two things there.

Gunnar Englund

www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

## RE: Accelerometer data post processing

## RE: Accelerometer data post processing

When you say 512 hertz, I assume that's your sample frequency?

## RE: Accelerometer data post processing

What you are describing sounds a bit like wavelet analysis, or STFT. it would be easy to do it in Matlab Scilab or Octave, but it would also be easy to get it wrong.

It'd probably help if you could give more detail of what the data looks like, and what you actually want in the way of results, as a general solution would be quite laborious to describe, and i suspect you don't need that.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

## RE: Accelerometer data post processing

-0.0367906

-0.00433198

-0.00831627

....

There is 1025243 lines in this file. Its the resuts of accelerometer from automotive vibrations. Measured with sampling rate 512Hz.

I would like to get a chart which describes which acceleration levels have the longest duration and occur most often.

## RE: Accelerometer data post processing

I recently had 28 gigabytes of data to analyse. Too much for any available(to us) analysis package. So, my colleague wrote a simple routine that sorted out regions that were above a certain, settable limit. We then got a set of smaller files that we could look at and plot from our ARCUS.

That was a very effective way of finding extreme vibration levels in data collected during about one month. We found six occasions that had lasted between two and five seconds each and I think you could do a similar thing. FFT and variations thereof is good for many things, but not necessarily for all things.

Gunnar Englund

www.gke.org

--------------------------------------

100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

## RE: Accelerometer data post processing

Gunnar Englund

www.gke.org

--------------------------------------

100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

## RE: Accelerometer data post processing

x - intervals of acceleration duration in seconds

y - average value of acceleration in these intervals

z - probability density of these intervals or the count how often did the average acceleration did occur

I am developing a device, which is supposed to extract with pendulum-like mechanism maximum amount of energy from random road accelerations. So in order to get max efficency for this this device I have to optimize the pendulum inertia and resistance to acceleration + acceleration duration values. It is not a vibration energy harvester, its swinging or bouncing energy harvester.

## RE: Accelerometer data post processing

## RE: Accelerometer data post processing

## RE: Accelerometer data post processing

The area under the acceleration curve (accel vs time) is the velocity.

## RE: Accelerometer data post processing

Are your data instantaneous acceleration values or are they rms values? I have the impression they are rms. Even if the negative values contradict that. Sampling with 512 Sa/s does not seem meaningful otherwise, since vibration data usually contain components in the kHz range.

I think it would be good to have all information possible instead of 'free thinking' in different directions.

www.gke.org

--------------------------------------

100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

## RE: Accelerometer data post processing

OK, you don't need FFTs. With a million points I wouldn't use Excel. I haven't seen a plot like the one you describe, although it is very similar to what we'd look at when taking roadloads for durability. There we don't bin by the length of each event, we just use a cumulative frequency plot.

Your proposed analysis needs a bit more definition.

Is the thing you are looking for describable as "duration of event in which RMS level (measured over what time?) exceeds a given level". You are going to have to define an averaging time for the RMS measurement, and I suspect you will end up binning the amplitude data.

I suggest you play around with a short sample to iron out the definition.

And I still think this is the wrong forum.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

## RE: Accelerometer data post processing

I haven't charted the final result. Also note that the sorting and histogramming are not live functions in excel, so this spreadsheet would need a lot of work before it was useable.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

## RE: Accelerometer data post processing

www.gke.org

--------------------------------------

100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

## RE: Accelerometer data post processing

This data post-processing field is too unknown for me :). I should do my homework properly. I´ll just start seeking handbooks and articles. Then I´ll get back to you if I am still in trouble.

Greglock, thanks for the spreadsheet. Question about it:

range F12 - there should be instead of A4 a B4 range?

## RE: Accelerometer data post processing

Range F12 - there should be inside equation instead of $A$4 a $B$4 range?

## RE: Accelerometer data post processing

There may be smarter ways to time each 'event' but since it is just proof of concept I didn't bother working out a neat method.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

## RE: Accelerometer data post processing

John D