How can I accurately test the variations between two accelerometers?

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Discussion Overview

The discussion revolves around methods to test and compare the performance of two accelerometers, exploring various experimental setups and the implications of different approaches. Participants consider both theoretical and practical aspects of measuring acceleration, including the effects of gravity and other forces.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests dropping the accelerometers from a height but expresses uncertainty about the calculations needed and the impact of drop height on readings.
  • Another participant proposes using a horizontal wheel to spin the accelerometers at controlled speeds to measure centripetal acceleration, arguing that dropping them could lead to damage and is difficult to control.
  • A different participant mentions using a pendulum setup with a string to test the accelerometers, questioning if the expected readings would be correct when swung from different angles.
  • It is noted that accelerometers measure proper accelerations, and the focus should be on comparing the outputs of the two devices rather than obtaining absolute values.
  • One participant points out that the accelerometers should read gravitational acceleration when stationary, and they can be tilted to measure varying values.
  • Concerns are raised about the feasibility of obtaining a horizontal wheel for controlled experiments, with suggestions for using an electric motor for speed control.
  • Another participant discusses the potential of using a toy car rolling down a slide but questions the necessity of knowing the acceleration beforehand for comparison purposes.
  • It is highlighted that various factors such as air resistance and friction complicate the measurement of acceleration in practical setups, reinforcing the preference for controlled conditions.
  • One participant raises a technical concern regarding the type of accelerometers being used, suggesting that piezo-based sensors may not be suitable for measuring constant accelerations.

Areas of Agreement / Disagreement

Participants express multiple competing views on the best experimental approach to compare accelerometers, with no consensus on a single method. There is also uncertainty regarding the implications of various factors affecting measurements.

Contextual Notes

Participants mention limitations related to air resistance, friction, and the need for precise setups, indicating that these factors could influence the accuracy of the experiments. The discussion also touches on the type of accelerometers used and their suitability for the proposed methods.

Who May Find This Useful

This discussion may be useful for individuals interested in experimental physics, engineering, or anyone looking to understand the practical challenges of measuring acceleration with different devices.

Branny12000
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Hi there I want to come up with an experiment to test two accelerometers to see how much they vary. I was thinking about dropping them each from a height but I am unsure how I could then work out what values I should be getting. Also does it matter what height I drop them from as I realize it would take some time to reach 9.8m/s2. Also would it be easier perhaps to drop them down a slide. I am very new to this area and so I am unsure about the calculations that would be needed and how they would relate to the readings which are in counts. ie 1g, 2g etc

Any help is much appreciated as I am a bit lost
Bran
 
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The best way would be by attaching them to a horizontal wheel, which you can spin with an accurately controlled angular speed. Then using the equation for centripetal acceleration you can check how far off they are at various speeds.

I would not recommend dropping, because it is too difficult to control, plus that can damage them permanently.
 
Hi there,

Well I was given a protractor and a piece of string so I suppose I could always do a simple experiment of fastening the accelerometer to the piece of string and allowing it to swing from different angles. So then for example if I allowed it to drop from 45 the maximum reading I should get it 1g in the horizontal direction (note I am testing tri-axial accelerometers). Is that correct?
 
Accelerometers measure proper accelerations, i.e., the accelerations that deviate them from free fall. In a pendulum-like set-up, those would be the accelerations due to the tension of the string; so they would be directed along the string, not horizontally (unless the angle of swing is greater than 90).

If your purpose is to compare two accelerometers, then you are not interested in absolute values of indicated accelerations. You just need to check whether they are the consistently close.
 
Just sitting still, the accelerometer should read gravitational acceleration of 9.8 m/s2.

If they are directional you can tilt them to get any reading between 0 and 9.8 m/s2
 
Thanks so much for your help. I see what you are saying about the string. The trouble is I don't know where I can get a horizonal wheel that I can alter the speed of at will.
 
Ps so in the string experiment the accelerometers should be measuring the tension in the string counteracting free fall hence if it is let go from 45 degree it should be gx(cos45)?
 
I do not know what your resources are. In principle, an electric motor with some frequency control would do it.

If you are very constrained, then the pendulum setup is probably the best you can have. You just need to make sure that you attach the accelerometers in the exact same way during all the trials, and record their output. You won't be able to calibrate them absolutely, but at least you can compare them to one another.
 
Branny12000 said:
Ps so in the string experiment the accelerometers should be measuring the tension in the string counteracting free fall hence if it is let go from 45 degree it should be gx(cos45)?

That will depend on the initial and the current position. A lot will depend on how much air resistance there is, that will also be felt as something pushing them from free fall.
 
  • #10
The other option I was thinking about was putting the accelerometer on a toy car and rolling it down a slide however, again I'm not sure how to work out the acceleration that would be experienced
 
  • #11
Why do you need to know the acceleration up front? If you only need to compare, why bother?
 
  • #12
Well we would also like to see how far off the actual value it is. It is not a definite consideration but osmething that we would ideally like to know also.
 
  • #13
That is complicated because you would need to take into account many things that you cannot easily control: air resistance, friction, varying gravity, and even centrifugal and Coriolis forces! That is why the controlled wheel is much preferred: it gives you a constant speed despite all those things, meaning a constant acceleration.
 
  • #14
I'm assuming you're using accelerometers that can measure down to dc? If they're piezo based sensors, they're designed for ac signals, so won't respond well to the relatively constant type accelerations you're discussing here. You'd need an oscillating acceleration... rotating imbalance, a sine wave played through a speaker or shaker, a vibrator etc...The followup is how are you measuring the output from the accelerometer...do you have a fixed readout, or are you putting a voltage signal into an oscilloscope or FFT analyser? If the latter, then you're looking at an AC signal.

Do you have the make/model # of the accelerometer?
 

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