Referring to the datasheet ADXL203, AN-1057 and CN-0189 I would like to implement a system that measures the angle of inclination of a vehicle (Roll, Pitch).
For the project I made the following choices:
- Power Supply ADXL203 5V
- Accelerometer is oriented on both its x-axis and y-axis
are parallel to the earth's surface
- Bandwidth Settings: 1Hz (Cx = Cy = 4.7 uF)
- RMS-noise (BW = 1Hz) = 138 ug (0.138 mg)
- RMS peak-peak = 6 x rms = 0.83 mg
- Tilt range ± 30 °
The Sensitivity ADXL203 is 1000 mV/g (typ). AN-1057 shows how to calculate the single axis acceleration (in my case both for the x axis and for the y axis):
Ax, out = 1g x sin (θ)
Ay, out = 1g x sin (θ)
Because the output resolution is a constant acceleration, the resolution in degrees of inclination is variable, with the best resolution close to 0° and the worst resolution at ±90°. The incremental sensitivity is the output change, shown in mg, per inclination angle step (In my case 1°).
For example, designing for a maximum step size of 1°, a resolution of at least 15 mg/LSB is necessary for a range of ±30°
What does mg/LSB mean? 15 mg to how many mV corresponds?
For example, suppose you want to use a two-input SAR ADC with Vdd = Vref = 3.3V. LSB = Vref / (2^n ) thus
n = 8 bits ---> LSB = 12.9 mV
n = 10 bits ---> LSB = 3.2 mV
n = 12 bits ---> LSB = 0.8 mV
Which is the best ADC resolution that should be chosen in my application? How can I estimate LSB in my application?
[edited by: mike_war at 9:55 AM (GMT 0) on 29 Jan 2019]