3DM-GX4
™
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Inertial Navigation System
User Manual
Sensor Measurements
23
4.1
Direct Sensor Measurements (IMU Outputs)
The sensors in an Inertial Navigation System (INS), from which measurements for navigation
and orientation are obtained, are collectively know as the Inertial Measurement Unit (IMU).
These sensors are arranged on the three primary axes (x, y, and z) to sense angular rate,
acceleration, and the local magnetic field . The gyroscopes are used to adjust the current
attitude estimate when an angular rate is sensed. The accelerometers sense gravity as well as
linear acceleration. The magnetometers sense the Earth’s magnetic field along with local
magnetic anomalies.
The IMU sensors can be read directly to report stand alone inertial measurements. Because
the sensor system is digital, the analog voltage readings from the sensors are converted into a
digital equivalent value based on the volt-to-bit scale of the internal analog to digital voltage
converter (A/D converter). For example, a 16-bit system will have 65536 A/D values (bits)
applied over the output voltage range of the sensor, typically splitting it in the middle for positive
and negative going signals (+/- 32768 bits). In the MIP Monitor software the conversion values
are not configurable, but there are user settable options for how the measurement is made.
These setting are available in the Settings > Device > IMU (tab). The context sensitive Help
menus (accessed with the Help button) provides explanations of the settings when hovered
over (
Figure 16 - IMU Settings
).
Figure 16 -
IMU Settings