The ST90 system is provided with a built-in motion sensor to provide electronic stabilization of the sonar beams. It is placed inside the Motor Control Unit. The motion sensor measures the roll and pitch movements of the vessel.

For improved operational accuracy, an external motion reference unit (MRU) can be used.

Offsets

The offset values specify the physical location of the motion reference unit relative to the reference point (origin). The relevant offset values can normally be taken from the vessel drawings.

Rotation

The values for rotation around the X, Y and Z axis are used to compensate for any misalignments made during the physical installation of the motion reference unit. Such misalignments occur if the sensor is not placed in parallel with the vessel’s horizontal and/or vertical planes. We strongly recommend that you install your motion reference unit so that all rotation angles can be set to 0 (zero).

The required accuracy of the offset and rotation angles depends on the accuracy requirements for the echo data.

The motion sensor offset values (its physical location relative to the vessels' coordinate system) are not important for sonar operation.

The Kongsberg Seapath^® - and other GPS systems - allow you to define the MRU location in the positioning system. If this is done, the MRU offset values in the ST90 system must be set to 0 (zero) to avoid "dual compensation". The rotation angles are normally not recorded by the positioning system. These can either be inserted into the MRU control application, or into the ST90 system. Make sure that you do not insert them both places.

1. Rotation around the x-axis: In the positive horizontal direction (forward), a positive rotation is clockwise.
2. Rotation around the y-axis: In the positive horizontal direction (starboard), a positive rotation is clockwise.
3. Rotation around the z-axis: In the positive vertical direction (down), a positive rotation is clockwise.
4. Reference point (Ship Origin)