System Description - SMC Networks IMU-007 User Manual

RMS
Root mean square (RMS) is a statistical measure of the magnitude of a varying quantity.

2 SYSTEM DESCRIPTION

The SMC motion sensors have three separate axial measurement component groups converting
signals from actual movements via three accelerometers and three gyroscopes into output data of
angles and attitude.
The output parameters are presented in a digital output string via RS422 and RS232.
The signal from the gyroscopes are combined with the signal from the accelerometers and are
processed in a Kalman filter inside the IMU to provide output value for acceleration, attitude and
angle with limited influence from noise and other inaccuracies.
Heave, surge and sway are calculated by integrating the acceleration in the X, Y and Z axis twice. The
integration is then filtered with a high pass filter.
The calculations of the distances are optimized for continuous motion and not for static distance
measurements, as the high pass filter will filter the position over time to zero.
The dynamic motion filtering is designed to measure motions over a period between 1 s and 25 s.
Before delivery all motion sensors are calibrated and the readings from the accelerometers and
angular rate gyroscopes are verified for alignment, linearity and temperature, to ensure they meet
the performance specifications.
The calibration is run up to +/-30 degrees of angle. The best performance is achieved within this
angle range.
If the motion sensor angle exceeds the calibrated angular range the calibration data will be
extrapolated outside the calibrated range, which may lead to decreased performance.
3
SMC IMU User Guide v26b.docx Index SMC Ship Motion Control