SBG Systems Ellipse AHRS User manual

Ellipse AHRS & INS
Use in marine applications
Operating handbook
Document ELLI SEOHSEA
Revision Jun 30, 2020
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Ellipse – Operating Handbook ELLI SEOHSEA
This operating handbook explains how to install and setup an Ellipse in marine applications
such as ship, ASV, ROV, or AUV. Mechanical installation is explained as well as software
configuration and magnetic calibration.
We recommend using the sbgCenter to configure the products, but this is also possible by
using our sbgECom C library.
Mechanical installation
Inertial Systems are very sensitive to their environment and the location of the inertial system
into the vessel is a key point to get accurate and reliable measurements.
Vibrations
The Ellipse is designed to handle vibrations. Nevertheless in case of highly vibrating
environment, an efficient mechanical vibration isolation is required for proper operation. Silicon
dampers can be used for that purpose.
Ellipse placement in the vessel
The vehicle coordinate frame is defined as follows:
●X axis points to the front of the vessel (bow)
●Y axis points to the right (starboard)
●Z axis points the bottom (keel)
The Ellipse MUST be mechanically aligned with the vehicle
coordinate frame, as explained in the following diagram.
Alignment accuracy should be better than 1°.
Note: If a correct mechanical alignment is not possible, then a software alignment
can be used. lease refer to the Ellipse User Manual for such operation.
The main lever arm is the signed distance,
expressed in the vehicle coordinate frame,
FROM the Ellipse center of measurements TO
the vehicle desired measurement point. It can
be used to deport the velocity and position
outputs to this specified location.
Only velocity and position outputs are
affected by this main lever arm measurement.
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Yaw
itch
Roll
X
Y
Z
1.15m
- 4.35m
IMUX
Z
Y

Ellipse – Operating Handbook ELLI SEOHSEA
Magnetic environment
If magnetometers are used for heading observation, user should also consider the magnetic
environment.
The Ellipse magnetometers require for good operation a clean magnetic field. The sensor
should be placed away from any magnetic interference such as: DC motors, radios, strobe
lights, power supplies etc.
GNSS Antenna placement
GNSS antenna must be fixed with respect to the Ellipse. It should have a clear view of sky.
The G S lever arm is the signed distance, expressed in the vehicle coordinate frame, from the
Ellipse center of measurements, to the GNSS antenna. It must be measured within 5cm
accuracy.
In addition, this lever arm should be lower than 10m for best performance.
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-0.95m
- 3.25m
ANT
IMUX
Z
Y

Ellipse – Operating Handbook ELLI SEOHSEA
Dual G S Antenna lacement
Dual antenna systems installation will require special care in order to obtain optimal
performance:
●Same antenna type, same cables with identical lengths must be used for both
antennas.
●Both antennas must be turned the same way (connectors oriented in same direction)
●Both antennas must have the same view of sky when mounted on the vehicle.
●Both antennas must be placed on a suitable location to avoid masks and reflections.
Once installed, the main G S antenna lever arm must be measured. It is the signed distance,
expressed in the vehicle coordinate frame, from the Ellipse center of measurements, to the
main G S antenna. It must be measured within 5cm accuracy. Then, the same should be done
for the second antenna.
recise lever arms can also be estimated in post processing using Qinertia.
Note: If the Ellipse is not physically aligned with the ship, lever arms are still taken to
the X, Y, Z reference frame of the ship. This is also the X, Y, Z reference frame of the
Ellipse considering the re-alignment has already been applied.
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Antenna 1
Antenna 2
X
Y
Z

Ellipse – Operating Handbook ELLI SEOHSEA
Software configuration
All Ellipse configuration is done through the sbgCenter interface, or using low level
communication protocol.
Note: At the first access, the Ellipse will have its default configuration. This data
output configuration should be used it you want to send logs to Support. Don't
hesitate to contact the Support Team for help.
Sensor
Motion rofile
For marine application, you can choose the relevant motion profiles
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Ellipse – Operating Handbook ELLI SEOHSEA
Alignment and lever arms
Here you can configure the alignment of the device and its lever arm in regard to the center of
rotation of the ship.
On the alignment settings you only need to set up the first two axis, then the third one will be
automatically computed.
Initial osition and Date
This parameter will matter if you are using magnetometers: the initial position and date will be
used to compute the magnetic declination.
In case you use magnetometers as a heading source, then a magnetic calibration is mandatory.
A 3D calibration should be preferred over a 2D one if possible. If a 2D magnetic calibration is
performed, it will be only valid locally, and should be re-done if the ship is in a different
geographic area.
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Ellipse – Operating Handbook ELLI SEOHSEA
Assignment
GNSS Receiver assignment
Here it is possible to select the serial port to receive the GNSS Receiver data, and select the
input Synchronization as well.
The Ellipse N and D GNSS are automatically set to “Internal” by default to select the on-board
GNSS Receiver. In addition, they accept In case the Internal GNSS Receiver is selected, the user
can also set an RTCM corrections input on any available serial port.
Other Aiding inputs
You can enable DVL aiding input for marine applications. lease note that Odometer is for
automotive application and Air Data for Airborne applications, so won’t be used here.
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Ellipse – Operating Handbook ELLI SEOHSEA
Aiding
GNSS Configuration
lease check following point at the G S configuration level:
1. Choose this parameter depending on the G S you are using (NMEA, Ublox, Novatel,
Septentrio)
2. Set up the lever arm of the G S depending on its position on the ship (GNSS Antenna
placement). If your lever arm has been precisely measured within 1-2 cm, or
estimated by Qinertia, you can check the " rimary antenna Lever arm has been
measured precisely" box. This will optimize Kalman filter warmup-time and overal
performance..
3. Select Rough lever arm if you measured it within 5cm accuracy. If precisely measured
or estimated by Qinertia, you can select "precise lever arm" to optimize filter warm-
up time and performance
4. Automatic rejection mode is advised for each parameter. Automatic mode
automatically detects the confidence so the Kalman filter knows it can rely more on a
parameter or less on an other.
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1
2
3
4

Ellipse – Operating Handbook ELLI SEOHSEA
Magnetic calibration in marine applications
When magnetometers are used as heading reference, a magnetic calibration is mandatory for
normal sensor operation. Different calibration methods are provided, depending on accuracy or
ease of use requirement.
Large ship calibration
In case the boat is a heavy ship and it is not possible to move it by hand, it will be necessary to
calibrate the magnetometers while cruising. The goal will be to collect data in every direction,
so you will have to make a 360° with the ship (the turn radius and speed does not matter).
You should prefer a 3D calibration if your boat can heel, if not then a 2D calibration should be
done.
The following procedure should be followed for good performance:
1. Install the sensor as described in previous sections, and place the whole system away
from external magnetic disturbances (buildings, other vessels, etc)
2. ress “Start acquisition” button on sbgCenter calibration window
3. Navigate in an 8 shape pattern, so you will be able to capture points in the Y-axis
while heeling slightly on both sides. It doesn’t need to be a critical angle, 20° would
be enough for instance, it has to be representative of the usual behavior of the ship.
4. Check that the 3D method is used (in case of very large ship, or when the roll/pitch
angles could not be changed significantly during calibration, a 2D method can be
used). ress “Calibrate” and check calibration results. ress “OK” to finalize the
calibration procedure.
5. ower cycle the sensor if you need immediate operation after calibration.
Light boat calibration (ASV, ROV, AUV)
As long as a boat is light enough to be held by a few persons (especially unmanned vehicles), a
3D calibration, made on the ground is to be preferred. The basic procedure remains the same,
and you should just rotate the system in as much orientations as possible.
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