limitations of accuracy in electronic scale

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limitations of accuracy in electronic scale

Post  Lev on Sat Nov 20, 2010 10:12 am

in one of the lectures when we were doing the exam Q example where we have a mass and a spring and we have to create a electronic scale to measure the mass.

one question is "discuss the limitations of the accuracy"

what exactly would we say for this? all i can think of is that the arduino has the accuracy of (1/1024)*5 for its analog inputs

i think though there might be some other things i am missing, any thoughts guys?

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Re: limitations of accuracy in electronic scale

Post  BBNT on Sat Nov 20, 2010 12:43 pm

I didn't do ESI but I would say generally two major limiations would be your sampling rate (and processing time of a sample) and the systems noise performance.

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Bryce

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Re: limitations of accuracy in electronic scale

Post  koya_smak88 on Sun Nov 21, 2010 2:14 am

What do you mean by system noise performance?

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Re: limitations of accuracy in electronic scale

Post  lewy78 on Sun Nov 21, 2010 9:22 am

In regards to 'noise performance', refer to the equation given by Peter, which is the Johnson-Nyquist Noise equation (look it up on wiki).

The 4 things identified by Peter were:

- Resolution of A2D conversion. we have to measure mass up to 1kg, so 1kg/(1024 quantisation levels) ~= 1g accuracy.

- The noise voltage as mentioned above

- The spring has no (explicit) damping. Therefore it will oscillate for some time after a mass has been placed on the contraption.

- In calculating the mass, we assume gravitational acceleration to be constant (ie. 9.8m/s^2) when it is actually location-dependent

One other thing is the tolerance and non-linearity of the slider pot. This will affect the voltage reading probably alot more than any of the other stuff.


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