Components and processing

The SMC marine motion sensors use solid state MEMS rate gyros that offer low noise and high accuracy as well as providing excellent vibration performance and long life reliability.

Three separate axial measurement component groups made of Gyroscopes, Accelerometers and Magnetometers are mounted in three axis for X, Y and Z measurements. The signal from the gyroscopes are combined with the signal from the accelerometers and magnetometers and are processed in a Kalman filter inside the motion sensor to provide output value for acceleration, attitude and angle with limited influence from accelerations, noise and other inaccuracies.

Heave is computed from a double integration of the acceleration into a linear position. The integration is further processed and filtered for an accurate heave measurement during dynamic environment.


Motion sensor Communication

As a standard all SMC marine motion sensors have 1 x RS232 and 1 x RS422 communication ports enabling the selection of Industry standard and bespoke output protocols. For aiding and data inputs 2 x RS232 serial ports are available. Ethernet connection is available as factory option, UDP output. Update Rates of 1 to 100Hz and 9600 to 115200 baud rates for selected protocols.


Aiding from Compass and GPS

SMC motion reference units can use inputs for aiding from standard industry GPS or Compass systems already installed on a vessel to improve measurement results during vessel turns. This is particularly useful for hydrographic surveying where 180° vessel turns between surveying lines is standard practice.


AHC Crane encoder feedback

Unique to the SMC motion sensor range is the SMC Active heave compensation AHC encoder feedback option. This was developed in conjunction with Bosch Rexroth drives but available for all users. The SMC AHC system accepts dynamic crane encoder position data, enabling continual calculation of the selected active heave measurement data to provide live motion compensation during critical marine crane operations.


Motion Sensor Configuration software

The marine motion sensor IMU configuration software enables quick and easy device setup in a structured display with user-friendly options and screen tabs for different industry applications.

Once the motion sensor has been mounted correctly it is easy to use the configuration software to modify the factory set up or change the configuration to a location/application specific installation.

Any setting changes made in the IMU Configuration software are written to the motion sensor flash memory that is not dependent on power supply or battery power.

Search functions and set up warnings provide protection against installation mistakes and the configuration can also be saved and exported to act as a backup and record of an installation.


Motion sensor protocols

SMC's standard NMEA 0183 protocol is just one of an increasing list of Industry Motion NMEA, Motion Binary and other common protocols (e.g. TSS1) that are installed as a default in the SMC motion sensors. These are all User Selectable from the SMC configuration software. The list includes Sector and Manufacturer standard protocols e.g. as used in the DP industry along with many Client Custom specific protocols that SMC has developed with our partners.

More information regarding the available protocols and details can be found in the SMC IMU Manual.


Calibration

Each motion sensor is calibrated prior to delivery. The motion sensors are thoroughly tested in the SMC facilities before and during the calibration process. The calibration is performed in a 2- axis rate table with a temperature controlled chamber. The calibration process is fully automated and runs for three days with a controlled temperature environment over the full temperature range.

All motion sensors are calibrated individually and the readings from the accelerometers and angular rate gyroscopes are verified for alignment, linearity and temperature, to ensure they meet the performance specifications.