Question

QUESTION 5 Describe how one can use accelerometers to determine orientation. What orientation would be measured? What are the limitations of this method?

Answer 1

Solution:

By default Accelerometers are sensitive to the difference between the linear acceleration of the sensor and the local gravitational field.The data sheet for any accelerometer will provide the positive x, y, and z axes on the sensor package and, by convention, these are defined so that a linear acceleration aligned in the direction of these axes will give a positive accelerometer output. However A gravitational field component aligned along the same axes directions will result in a negative reading on the accelerometer.

Measurement Procedure:
The acceleration is measured by the deflection of proof mass from it's actual position.The upper proof mass is suspended by the restoring springs. Both a gravitational field directed to the left and a linear acceleration of the package to the right will deflect the proof mass to the left.
The deflection of the proof mass is measured from the change in capacitance between the fingers of the proof mass and the sensing plates.A simplified transducer model and equivalent electrical circuit are shown

Simplified Model Equivalent Circuit possible diflection in any direction Proof Mass

Axis orientation example:
The accelerometer used in a smartphone had the following orientation aligned in the circuit board
• The x-axis is aligned along the body axis of the smartphone
• The z-axis points downwards so that it is aligned with gravity when the smartphone is flat on a table
• The y-axis is aligned at right angles to both the x and z axes so that the three axes form a right handed coordinate system.