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How to compare noise levels between digital and analog accels?

Question asked by david234589 on Jan 28, 2014
Latest reply on Jan 28, 2014 by neilzhao

Analog accelerometers e.g. ADXL103, have noise levels quoted as micro-g-per-root-hertz. For that one it's around 100 micro-g/rtHz. This is a spectral quantity (i.e. it is the noise in a certain bandwidth).

 

Digital accelerometers e.g. ADXL345 have noise levels quoted as "LSB rms". This is not a spectral quantity but just an rms quantity.

I'm guessing that for that digital accelerometer with approximate numbers of: Sensitivity = 200 LSB/g and Noise = 1 LSBrms, that it has noise level of: (1 LSBrms)/(200 LSB/g) = 5 milli-g rms.

 

How is the best way to compare between the two, apples-to-apples? Is it to say, I decide to electronically filter everything above 1kHz from both the ADXL103 and the ADXL345 signal, and therefore the bandwidth in both cases is 1kHz, and therefore:

ADXL103 has (100 micro-g/rtHz)*(sqrt(1kHz)) = 3 milli-g rms? Is that true?

 

However I notice ADXL has user-selectable bandwidth/datarate. How to factor this in?

 

Ultimately I just want to take a digital and an analog accelerometer and say which one is better in terms of noise.

 

Thanks!

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