Question
Im interested in purchasing the ADXL001 MEMS Accelerometer Eval Board. Howeverthe noise floor is of concern. What is the best way I can go about measuringthe noise floor of this device since I understand there is an offset voltage ofaround 1V when the device is stationary at 0g? So will I not be able tomeasure the noise floor since it will always show a signal of 1V? Any helpwould be of great benefit.
Answer
The 1g measurement you refer to depends on the orientation of the device.
The ADXL001 is sensitive in the x-axis (sensitive axis in the plane of the chip ), so I would expect to measure 0g when the part is placed flat.
The part can operate on voltage supplies from 3.3 V to 5 V, so the 1g sensitivity and offset will be ratiometric to Vs.
The 0g offset will vary from 1.65V to 2.5V or Vs/2.
To calculate the noise:
Take the noise density: 3.3 mg/sqrtHz - datasheet 70g Version
(3.3mg/sqrtHz*sqrt(22000*1.3) = 558mg Noise
1.3= correction factor as the low pass filter is not ideal
With a sensitivity/scale factor of 16mV/g
558mg of Noise is equal to 8.9 mV Noise
Please keep in mind the ADXL001 is designed for high full scale range applications, where the resolution of the signal is not terribly important. Assuch, the noise floor would appear much higher than some of our other low-noise accelerometers such as ADXL203, ADXL345, ADXL362 which have lowerfull scale ranges.