Data Sheet

ADXL103/ADXL203

Rev. D | Page 15 of 16

USING THE ADXL103/ADXL203 WITH OPERATING

VOLTAGES OTHER THAN 5 V

as 6 V. Some performance parameters change as the supply

voltage is varied.

The ADXL103/ADXL203 output is ratiometric, so the output

sensitivity (or scale factor) varies proportionally to the supply

The zero g bias output is also ratiometric, so the zero g output is

The output noise is not ratiometric but is absolute in volts;

therefore, the noise density decreases as the supply voltage

increases. This is because the scale factor (mV/g) increases

noise density is typically 190 μg/√Hz.

Self test response in g is roughly proportional to the square of

the supply voltage. However, when ratiometricity of sensitivity

is factored in with supply voltage, self test response in volts is

roughly proportional to the cube of the supply voltage. So at

150 mV or equivalent to 270 mg (typical).

The supply current decreases as the supply voltage decreases.

USING THE ADXL203 AS A DUAL-AXIS TILT SENSOR

One of the most popular applications of the ADXL203 is tilt

measurement. An accelerometer uses the force of gravity as an

input vector to determine the orientation of an object in space.

An accelerometer is most sensitive to tilt when its sensitive axis

is perpendicular to the force of gravity, that is, parallel to the

earth’s surface. At this orientation, its sensitivity to changes in

tilt is highest. When the accelerometer is oriented on axis to

gravity, that is, near its +1 g or –1 g reading, the change in

output acceleration per degree of tilt is negligible. When the

accelerometer is perpendicular to gravity, its output changes

nearly 17.5 mg per degree of tilt. At 45°, its output changes at

only 12.2 mg per degree, and resolution declines.

Dual-Axis Tilt Sensor: Converting Acceleration to Tilt

When the accelerometer is oriented so both its x-axis and y-axis

are parallel to the earth’s surface, it can be used as a 2-axis tilt sensor

with a roll axis and a pitch axis. Once the output signal from the

accelerometer has been converted to an acceleration that varies

between –1 g and +1 g, the output tilt in degrees is calculated as

Be sure to account for overranges. It is possible for the

accelerometers to output a signal greater than ±1 g due to

vibration, shock, or other accelerations.