Accelerometer Noise
Accelerometer Noise
(OP)
Hello my EE friends,
First, I'm sorry for the amateur question. Second, I'm hoping this is the correct forum, since double posting is a grievous sin.
I set up what I thought was plain vanilla instrumentation to measure and record structural vibrations.
Teensy 4.1 (with simple Arduino code) and an 3-axis ADXL 335 accelerometer (+/- 3.0g with 3.3V input) on an Adafruit board.
https://www.adafruit.com/product/163
I am getting a lot of apparent noise with my application.
So I attached my accelerometer to my bike crank and collected some plain vanilla data (i.e. about 2 Hz). Still getting way too much noise. That is, I see lots of jitters - many reversals in the acceleration that are unrealistic. I am also getting a couple of high spikes in acceleration that are unrealistic. See figure below (better resolution in attached Excel graph).
Could this be my code, or the accelerometer? I've got nothing fancy at all. Thanks in advance for any suggestions.

https://res.cloudinary.com/engineering-com/image/upload/v1615993342/tips/X_ACCDATA_BikeCrank_01-20210316b_tvaymu.pdf
First, I'm sorry for the amateur question. Second, I'm hoping this is the correct forum, since double posting is a grievous sin.
I set up what I thought was plain vanilla instrumentation to measure and record structural vibrations.
Teensy 4.1 (with simple Arduino code) and an 3-axis ADXL 335 accelerometer (+/- 3.0g with 3.3V input) on an Adafruit board.
https://www.adafruit.com/product/163
I am getting a lot of apparent noise with my application.
So I attached my accelerometer to my bike crank and collected some plain vanilla data (i.e. about 2 Hz). Still getting way too much noise. That is, I see lots of jitters - many reversals in the acceleration that are unrealistic. I am also getting a couple of high spikes in acceleration that are unrealistic. See figure below (better resolution in attached Excel graph).
Could this be my code, or the accelerometer? I've got nothing fancy at all. Thanks in advance for any suggestions.

https://res.cloudinary.com/engineering-com/image/upload/v1615993342/tips/X_ACCDATA_BikeCrank_01-20210316b_tvaymu.pdf
RE: Accelerometer Noise
Got a picture of your on-bike setup?
If you set the accelerometer on a piece of foam rubber and hold your breath what do you get?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Accelerometer Noise
-AK2DM
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"It's the questions that drive us"
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RE: Accelerometer Noise
Little noise when sitting still.
Much noise with even very small movement.
1. do I have the wrong accelerometer? It costs about $20 thru Adafruit. I can spend $7 or $100 on an accelerometer. Not sure how to differentiate based on data sheets. All appear to have capacitors on board and very little noise.
2. Is this level of noise - especially the slow movement in the 6 to 8s range - typical? Unfortunately, this doesn't work for me, as I'm trying to measure structural vibrations and the different between 0.05g and 0.08g is non-trivial.
3. Calibration drift. I manually calibrate the accelerometer "by hand" flipping the accelerometer 180 deg for each axis and viewing the output pins (if there's an easier way, I'd like to know). I did notice drift in a short time. A lot of drift even after 3 minutes. The accelerometer was getting warm after 10 minutes, so I disconnected. Is that normal?
What's the best path forward if I'm trying to measure +/- 2.0 g with 2% accuracy, and sampling systems with less than 10 Hz?
https://res.cloudinary.com/engineering-com/image/upload/v1616080672/tips/ACCDATA_desktop20210318_n6enea.pdf
RE: Accelerometer Noise
RE: Accelerometer Noise
See https://www.analog.com/media/en/technical-document...
RE: Accelerometer Noise
Wonder if you are picking up extraneous noise from the sprockets/chain system?
-AK2DM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
RE: Accelerometer Noise
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Accelerometer Noise
This is actually serious and professional.
The bike crank in my garage was my attempt at trouble-shooting. To be clear, this is not about bike cranks but instead structural instrumentation on a shake table.
Attached is the shake table accel data, which is the source of my troubles. The bike crank test just provided a confirmation that noise was not just a function of the table.
Shake table input: f = 2.0Hz, A = 5mm. Nema 34 Servo (Teknic) has been auto-tuned already.
https://res.cloudinary.com/engineering-com/image/upload/v1616097386/tips/ACCDATA_2.0Hz5mm_post-AutoTune20210315_wwuhap.pdf
RE: Accelerometer Noise
RE: Accelerometer Noise
If you take a small loop of wire and hook it to a sensitive scope or meter just waving it around cuts DC magnetic field lines caused by things around you including the earth's own field. The more of the earth's field you encompass the more noise you 'create' with movement.
Typically you'd go to great pains to the shield your setup to prevent this. Then you'd do things like amplify the signal to 0-10V and send that down the long wires to the 'input'. Then any uV or mV noise is washed out.
Ideally you get your seismic system setup such that you send power out to the sensor it does all the G sensing right at that spot then pumps out data RS485 type data (numbers) that can't be bugged by wire runs at all. One normally wouldn't take the raw analog data very far and by far I mean more than 6 inches. If you want a noiseless system don't take it more than 2 inches and do that carefully.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Accelerometer Noise
I've mounted my accelerometer right next to my board with jumper wires about 4". Noise is significantly reduced to the equivalent of about 0.02g (which is good enough for my application of -1.0 to 1.0g range).
Rookie mistake. Next time I'll come to the forum with better questions.
RE: Accelerometer Noise
Keith Cress
kcress - http://www.flaminsystems.com