Table of Contents
Advertisement
Guidance
Magnetometer Calibration
Calibration Process
The magnetometer calibration encompasses three areas: (a) hard-iron calibration, (b) soft-iron calibration
and (c) magnetic disturbance calibration.
Hard and soft-iron calibration allows the following equation to be used, and corrects for hard and soft-
iron effects due to nearby ferrous metals and magnetic fields. This calibration is necessary in order to
achieve valid compass heading readings:
Image not found
In addition, using the same calibration data the strength of the Earth's Magnetic Field is determined.
Whenever the data from the magnetometer indicates the current magnetic field differs from the calibrated
Earth's Magnetic Field strength by more than the "Magnetic Disturbance Ratio", a Magnetic Anomaly is
declared.
Therefore, careful and accurate Magnetometer Calibration is crucial in order to yield valid compass
heading, 9-axis heading and magnetic disturbance detection.
Magnetometer Calibration can be accomplished with a single, simple calibration process through the use
of the
Magnetometer Calibration
communicate to the navX-sensor circuit board via a USB cable.
A gyroscope measures the amount of angular rotation about a single axis. Since the gyroscope measures
changes in angular rotation, rather than an absolute angle, calculation of the actual current angle of that
axis is estimated via
numerical integration
Any Inertial Measurement Unit (IMU), including a navX-sensor, that integrates a signal from a gyroscope
will also accumulate error over time. Accumulated error is due to several factors, including:
Quantization noise
continuous analog value to a discrete integral value)
Scale factor error (which occurs due to manufacturing errors causing a specified scale factor [e.g.,
256 bits per unit G] to be incorrect)
Temperature instability (which occurs when a sensor is more or less sensitive to an input as
temperature changes)
Bias error (which occurs because the value the sensor reports at 'zero' is not known well enough
to 'subtract' that value out during signal processing)
Over time, these errors accumulate leading to greater and greater amounts of error.
tool. This tool is designed to run on a Windows computer, and
Yaw Drift
rather than an exact measurement.
(which occurs when an analog-to-digital converter (ADC) converts a
73
Advertisement
Table of Contents
