Magnetic Calibration
Static magnetic interference is resolved through magnetic calibration. Dynamic magnetic interference is compensated by a filter algorithm, but should be minimised where possible by selecting the best possible mounting location or implementing magnetic shielding — see Magnetics for more information. To compensate for static magnetic interference, magnetic calibration should be performed whenever the Certus mounting location or operation environment changes.
Certus contains a dynamic magnetic compensation filter that is able to mitigate the effects of short term magnetic interference sources while in operation. For example, if Certus is installed in a car and the car drives over a large piece of magnetised steel, this will be compensated for. Another example is driving through a tunnel which is built from reinforced concrete, which can distort the local magnetic field substantially. It is important to note that for the Certus dynamic magnetic compensation filter to operate correctly, Certus needs to get a GNSS fix at least once every time it is moved more than 50 km. Each time Certus moves more than 50 km the new position is stored permanently and allows Certus to update its world magnetic model values.
There are three types of magnetic calibration available: 2D calibration, 3D calibration and automatic calibration. The three magnetic calibration types and their respective typical applications are described as follows.
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2D calibration involves at least one full rotation of the vehicle about the Z-axis and is designed for vehicles that are not intended to travel whilst turned upside down, such as full-sized cars, passenger planes and boats.
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3D calibration involves at least two full rotations of each axis (X, Y and Z) and is designed for vehicles that are intended to be manoeuvred and travel upside down, such as underwater vehicles. 3D calibration offers slightly better performance, and is recommended where possible. Be mindful that the support mechanism used to support the vehicle during calibration can influence the results.
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Automatic magnetic calibration continuously and automatically calibrates for static magnetic interference while the unit is in operation. While it is not as accurate as 2D or 3D calibration, and can take significantly longer to calibrate, automatic magnetic calibration is very convenient for applications where it is impractical to employ those methods.
Note: If Certus is going to be used in a vehicle, the calibration should be performed while Certus is mounted in and fixed to that vehicle. This means that the whole vehicle must be moved to perform the calibration. The calibration needs to be performed in an area away from other sources of magnetic interference. For example if Certus is installed in a car, the calibration should not involve driving over steel drains or reinforced concrete etc. If Certus is being calibrated to operate standalone, the calibration should not be done on a desk with a steel frame.
2D Magnetic Calibration
The following procedure should be used to perform a 2D magnetic calibration.
2D Magnetic Calibration Using the web UI or Certus Manager Software
- The unit should be powered on while the vehicle is in a level orientation and kept stationary. It is recommended this be done in an outdoor area away from metal or obstructions.
- After power on wait 5 minutes for the temperature and filter to stabilise.
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Open
- In the Tools menu, open Magnetic Calibration. Click the 2D Calibration button.
- Whilst keeping as level as possible, rotate the vehicle in either direction through one and a quarter full rotations. In a car or boat his can be achieved by driving in one and a quarter circles.
- Check the status in the Magnetic Calibration window to ensure that the calibration completed successfully. If not successful, click Cancel, wait 2 minutes and repeat from step 4.
Note: Do not press the Save button in the lower half of the page, this will overwrite the new calibration values. The auto-generated calibration values are automatically saved internally by Certus.
2D Magnetic Calibration Using the Packet Protocol
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The unit should be powered on while the vehicle is in a level orientation and kept stationary.
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After power on wait 5 minutes for the temperature and filter to stabilise.
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Ensure that the device has a position fix, either from an external GNSS receiver, or using the External Position and Velocity packet #44 or the External Position packet #45, before proceeding.
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Send the Magnetic Calibration Configuration Packet with the action Start 2D Magnetic Calibration.
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Whilst keeping as level as possible, rotate the vehicle in either direction through one and a quarter full rotations. In a car this can be achieved by driving in one and a quarter circles.
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Read the Magnetic Calibration Status Packet to ensure that the calibration completed successfully. If not successful, send the Magnetic Calibration Configuration Packet with the action Cancel, wait 2 minutes and repeat from step 4.
3D Magnetic Calibration
The following procedure should be used to perform a 3D magnetic calibration.
3D Magnetic Calibration Using the web UI or Certus Manager Software
- The unit should be powered on and the vehicle kept stationary. It is recommended this be done in an outdoor area away from metal or obstructions.
- After power on wait 5 minutes for the temperature and filter to stabilise.
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Open
- In the Tools menu, open Magnetic Calibration. Click the 3D Calibration button. The following steps 5, 6 and 7 can be performed in any order.
- Slowly rotate the vehicle twice around the X-axis (roll).
- Slowly rotate the vehicle twice around the Y-axis (pitch).
- Slowly rotate the vehicle twice around the Z-axis (heading).
- Check the status in the Magnetic Calibration window to ensure that the calibration completed successfully. If not successful click Cancel, wait 2 minutes and repeat from step 4. Do not press the save button in the lower half of the page, this will over write the new calibration values. The auto-generated calibration values are automatically saved internally by Certus.
3D Magnetic Calibration Using the Packet Protocol
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The unit should be powered on and the vehicle kept stationary.
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After power on wait 5 minutes for the temperature and filter to stabilise.
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Ensure that the device has a position fix, either from an external GNSS receiver, or using the External Position and Velocity packet #44 or the External Position packet #45, before proceeding.
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Send the Magnetic Calibration Configuration Packet with the action Start 3D Magnetic Calibration. The following steps 5, 6 and 7 can be performed in any order.
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Slowly rotate the vehicle twice around the X-axis (roll).
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Slowly rotate the vehicle twice around the Y-axis (pitch).
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Slowly rotate the vehicle twice around the Z-axis (heading)
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Read the Magnetic Calibration Status Packet to ensure that the calibration completed successfully. If not successful, send the Magnetic Calibration Configuration Packet with the action Cancel, wait 2 minutes and repeat from step 4.
Automatic Magnetic Calibration
Automatic magnetic calibration is an algorithm that continuously and automatically calibrates for static magnetic interference. Automatic magnetic calibration is enabled by default and it is recommended to keep it enabled for all vehicle types. When used on top of a 2D or 3D calibration it can give the best results from magnetic heading.
The automatic calibration for 2D vehicles differs from that for 3D vehicles. To ensure the correct calibration is being applied, ensure the correct vehicle profile is selected for your application in the
2D Vehicle Profiles
2D vehicles are those which cannot easily or safely be turned upside down, and typically include vehicles such as cars and bicycles.
Each time Certus is powered on in a cold start (48 hours without power) the automatic calibration is reset. The automatic magnetic calibration starts operating when Certus is travelling at a speed over 5 m/s with a GNSS fix and either dual antenna is the heading source or velocity heading is turned on.
Automatic magnetic calibration is not as accurate as 2D or 3D calibration, however, it is sufficient for most vehicles and allows Certus to be installed into vehicles and operated without user intervention.
Automatic magnetic calibration can be turned off using the
3D Vehicle Profiles
3D vehicles are those which can easily or safely be turned upside down, and typically include vehicles such as humans, underwater vehicles and fixed wing planes.
Each time Certus is powered on in a cold start (48 hours without power) the automatic calibration is reset, and a new calibration will begin if a significant change in calibration values is detected. The automatic calibration for 3D vehicle profiles requires no prior calibration or minimum velocity to begin.
The calibration time is dependent upon the rotation about each axis; approximately, 1 degree of uniform motion in each axis will take up to an hour to converge, motion as low as 0.2-0.5 degrees will take upwards of 12 hours to converge, and 10 degrees of motion will take around 40 seconds to converge. These time estimates are dependent on the environment and nature of the motion.
Automatic magnetic calibration can be turned off using the
Disabling Magnetometers
In situations where there are very strong dynamic magnetic disturbances present, it is recommended to disable the magnetometers. When the magnetometers are disabled, an alternative heading source is required or else Certus may become inaccurate. Dual antenna heading is the recommended source. See Heading Sources for information. The magnetometers can be disabled using the Magnetic Heading setting on Filter Options page in the