ADIS16203
Rev. A | Page 11 of 28
THEORY OF OPERATION
OUTPUT RESPONSE
The ADIS16203 is a calibrated digital inclinometer that provides a
full 360° of measurement range in any rotational plane that is parallel to
the earth’s gravity. A dual-axis accelerometer provides the base-sensing
function, which resolves the earth’s gravity into two orthogonal vectors,
as displayed in Figure 23. A power-efficient approach to a common
trigonometric identity converts these orthogonal vectors into an incline-
angle measurement.
The incline-angle measurements are linear with respect to
degrees, and the sensor’s orientation produces the output
response displayed in Figure 25. This figure is helpful in
understanding the basic orientation of the inertial sensor
measurement axes.
BOTTOM
VIEW
(Not to Scale)
INCL_OUT = +270°
INCL_180_OUT = –90°
INCL_OUT = 180°
INCL_180_OUT = 180°
INCL_OUT = 0°
INCL_180_OUT = 0°
0°
INCL_OUT = 90°
INCL_180_OUT = 90°
EARTH’S SURFACE
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EARTH’S SURFACE
1g
1g
a
2
a
1
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Figure 23. Sensor Measurement Diagram
The digital postprocessing circuit digitizes the sensor outputs
and applies sensitivity/offset calibration coefficients prior to angle
calculations. A factory calibration produces these coefficients using
a full 360° mechanical rotational apparatus. This eliminates the need
for system-level calibration in many cases. In addition to calibrating
the sensor elements, the ADIS16203 corrects for power-supply-
dependent parameters, providing a more robust calibration.
Figure 25. Output Response vs. Orientation
The accuracy of the incline-angle measurements relies on three
important factors: the absence of external (aside from gravity)
acceleration, managing offset errors introduced during system-level
configuration, and maintaining a proper axis of rotation (rotation
plane parallel with earth’s gravity). All of these factors can influence
the acceleration measurements and introduce error. The ADIS16203
provides a simple method for calibrating configuration errors by
providing the INCL_NULL register function. See the Calibration
section for more details. In addition, a 10° tilt plane error can
introduce as much as ±1° of error in the incline-angle outputs.
TEMPERATURE SENSOR
An internal temperature sensor monitors the accelerometer’s
junction temperature. The TEMP_OUT data register provides
a digital representation of this measurement. This sensor provides
a convenient temperature measurement for system-level charac-
terization and calibration feedback.
SYSTEM-LEVEL ORIENTATION OFFSET
TILT PLANE ERROR
IDEAL = 90°
PCB
ATTACHMENT
OFFSET
EARTH’S SURFACE
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Figure 24. ADIS16203 System-Level Orientation
