Impacts on the accuracy of a capacitive inclination sensor

The measurement of inclination by evaluating changes of coupling capacitances caused by movements of a fluid in a circular tube is a well known approach. Based on a fluidic inclinometer with an accuracy of better 0.2/spl deg/ over full circle measurement range without calibration, the effects of axis tilt and fill level variation are studied. It is shown that changes of physical properties of the fluid over industrial and automotive temperature ranges, inaccurate fill level and sensor axis tilt are compensated by the evaluation algorithm whereas a tilt between sensor axis and system axis leads to a systematic difference between inclination measured by the sensor and true rotation around the system axis. This effect which is common to all inclination sensors can either be compensated by in-system calibration or corrected if the misalignment is known or avoided by precise alignment of the axis.