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3DM-GX4
™
-45
™
Inertial Navigation System
User Manual
Performance Optimization
35
5.
Performance Optimization
5.1
Magnetometer Calibration
Although the 3DM-GX4 -45
™
magnetometers are calibrated at the factory to zero- out any
magnetic influences internal to the device, measurements are still subject to influence from
external magnetic anomalies when the sensor is installed in the user's end application. These
anomalies are divided into two classes: hard iron offsets and soft iron distortions. Hard iron
offsets are created by objects that produce a magnetic field. Soft iron distortions are considered
deflections or alterations in the existing magnetic field. Ideally, these influences are mitigated by
installing the sensor away from magnetic sources, such as coils, magnets, and ferrous metal
structures and mounting hardware. However, often these sources are hard to avoid or are
hidden.
When using the 3DM-GX4-45
™
magnetometer to aid in heading estimations, a field calibration
of the magnetometer after final installation is highly recommended. This can be accomplished
using LORD MicroStrain
®
MIP Hard and Soft Iron Calibration software. This software is
included with the MIP Monitor Software Suite (
see Software Installation on page 11
).
The following are instructions for field calibrating the magnetometers.
1. Connect and power-on the sensor as normal.
2. Open the MIP Hard and Soft Iron Calibration software.
3. Select the sensor to be calibrated, and then select Collect Data (
Figure 24 - Collect
Calibration Data
). The software will begin taking readings, as indicated by the points
counter in the graphing window.
4. As the readings are taken, rotate the sensor or sensor platform in all possible
directions to get a complete profile of the baseline magnetic influences throughout the
sensor frame. Data points will appear on the graph in red. For mobile sensor
platforms, such as ground vehicles, move the platform as much as possible to
simulate actual use without exposing it to excessive magnetic sources (like driving
over railroad tracks or near steel pilings). The intention is to get a baseline value of the
platform in a neutral environment but one that still accounts for the platform itself in all
orientations.