# ADXL203: Measuring tilt angles

Document created by analog-archivist on Feb 23, 2016
Version 1Show Document

### Q

In my project i want use accelerometer ADXL203 for measurement of the corner of
the tilt. I interest what measure tilt corner each of axises to perpendicular
planes of the Earth when accelerometer is simultaneously tilt on axises X and Y
on some corners?

### A

Some notes on Tilt for the ADXL202. The ADXL203 should be the same but changing
the specifications according to the datasheet.

The noise in the ADXL202 is specified as 500ug/sqrt(Hz) typically. The total
noise therefore depends on the bandwidth. You as the system designer can
control the bandwidth of the accelerometer using the capacitors Cx and Cy.
Large values of Cx and Cy will reduce the bandwidth and reduce the noise. The
bandwidth is given by:
Noise bandwidth = 1.57 / (2 x PI x C x R)

Where C is the value of Cx or Cy, and R is the value of Rset which is nominally
32kOhm.

For a noise bandwidth of 1Hz, the total noise is 500ug, for a noise bandwidth
of 100Hz, 5mg.

You are measuring the angle of tilt by measuring the component of the
acceleration due to gravity which is along the measurement axis of the
accelerometer. The angle (theta)  and the measured acceleration (X) are related
by simple geometry as:
X = Sine (theta)

Assuming you can limit the noise bandwidth to 1Hz, we now convert the noise to
it's equivalent angle:
Theta = sin-1 (X) = 0.029 degrees.

However, you'll need to calibrate the ADXL202 ( as described in the datasheet
and app notes), which normally consists of exposing the accelerometer to +/-1G,
recording the maximum excursion and calculating the calibration co-efficients.
You'll also need to take care with the temperature drift which is typically
2mg/degC. You can either recalibrate when ever there is a change in ambient
temperature or store different calibration co-efficients for a range of
temperatures and measure the ambient temperature.