Q1-Can we assume that the "Noise Density" specified in the ADXL150/250 datasheet
is the same as "the Resolution" of this sensor?
2-Are we able to measure the acceleration value less than 5g by ADXL150/250?
A1) The resolution depends on the bandwidth and can be calculated by the formula
Noise ( rms ) = 500 x (square root( BW x 1.5))
The smaller the bandwidth is, the less aliasing of noise you have at the
output and the better the resolution.
If you have a resolution of +/- 5mg at 60 Hz it doesn't mean that you have
2/0.005 different possible positions. It's the minimum accuracy reading you can
have. You can't talk about positions because it is not a discrete system.
2)see page 10 of the datasheet…The limiting resolution is predominantly set by
the measurement noise “floor,” which includes the ambient background noise and
the noise of the ADXL150/ADXL250 itself. The level of the noise floor varies
directly with the bandwidth of the measurement.
When the device bandwidth is rolled off to 100 Hz, the noise level is reduced
to approximately 10 mg…you must also look at the offset and sensitivity scaling
to determine if the ADXL150 is a suitable solution for a low G application.