KONGSBERG Seatex MRU 5 practical combat

3.2 Mechanical fixation and vibration reduction

The MRU 5 shell is made of aluminum alloy and weighs approximately 1kg. It is fixed with 4 M5 stainless steel bolts. Due to the continuous vibration of the vessel (0.5 m/s ², 10-2000Hz), no additional shock absorbers are required - its internal sensors have anti vibration design. But it is necessary to avoid resonance with the ship structure, which can be confirmed by measuring the vibration spectrum during trial operation.

3.3 Leverage arm compensation setting

When MRU 5 is not installed at the center of gravity (CG) of the vessel, three offsets need to be entered in the Seatex MRC configuration software:

Dx: Longitudinal distance from the center of the sensor to CG (positive front and negative back, meters)

Dy: Horizontal distance (right positive left negative)

Dz: Vertical distance (positive top and negative bottom)

For example, if the sensor is installed on the bridge deck and the CG is 3 meters below the main deck, then dz=-3.0. These parameters are used to convert the acceleration and angular velocity measured by the sensors into real motion at the CG. Incorrect lever arm values are the primary cause of heave errors.

Electrical interface and communication configuration

4.1 Power Connection

MRU 5 accepts 12-30V DC (maximum power consumption of 11W). It is recommended to use a dedicated branch of the 24V emergency distribution board for ships, connected in series with a 1A fast melting fuse. It is recommended to use 0.75mm ² twisted pair shielded wire for the power cord, with positive and negative terminals of PWR+and PWR - respectively. After power on, the panel LED indicator lights will light up in the following order:

Green constantly on: power supply is normal

Orange flashing: starting self-test (about 10 seconds)

Green flashing: Data output is valid

4.2 Overview of Communication Ports

MRU 5 provides multiple serial interfaces:

Main serial port (COM1): RS-232/RS-422 switchable, used for bidirectional binary protocol or ASCII output.

Auxiliary serial port (COM2): RS-232, used for external speed input (VG/VWW, etc.).

Heading input port (COM3): CMOS level, used for external heading data (HDT/HDM) or synchronous triggering.

All baud rates are configurable (4800 to 115200 bps). Recommend using 115200 bps to ensure no packet loss during 100Hz output.

4.3 Protocol Selection and Configuration (MRC Software)

The accompanying Seatex MRC configuration software (Windows compatible) is connected to MRU 5 via a USB to RS-232 cable. Main configuration steps:

Select output variables: Check the required items from 189 variables. Typical multibeam applications require: Roll, Pitch, Heave, Heading, HeaveRate.

Set output format:

Binary (IEEE 32-bit floating-point): The most efficient and recommended for DP systems.

NMEA 0183 proprietary statements, such as $PSXROT and $PSHEV, are used for compatibility with older devices.

Third party sonar format: MRU 5 has over 20 common protocols built-in, including Simrad EM 1000, Atlas Fansweep, Reson Seabat, and more. Simply select the corresponding model from the drop-down menu without writing string parsing code.

Set output rate: 1Hz, 5Hz, 10Hz, 20Hz, 50Hz, 100Hz. It is recommended to use binary format at 100Hz, otherwise ASCII will occupy a lot of bandwidth.

Configure external inputs: Enable speed input (to improve heave accuracy during steering), select NMEA statement type (VTG, VHW, or VBW) and input baud rate.

Save configuration to MRU 5 non-volatile memory: no loss upon power failure.

Accuracy characteristics and performance optimization

5.1 Interpretation of Official Accuracy Indicators

Parameter numerical conditions

Static roll/pitch accuracy 0.025 ° RMS, stationary for 30 minutes

Dynamic roll/pitch accuracy 0.030 ° RMS ± 5 ° amplitude, 5-minute biaxial sinusoidal motion

The dynamic accuracy of lifting and sinking is 5cm or 5% (whichever is greater) with a period of 0-25s, and the effective wave height can reach 50m

Angular velocity noise 0.025 °/s RMS for all axes

Acceleration noise 0.0020 m/s ² RMS-

The heave drift can be ignored and the short-term recovery after turning can be ignored

Practical application precautions:

When the heave value is less than 5cm, the absolute error may reach 5cm, which should be considered as the effective resolution limit under micro wave conditions.

The dynamic roll accuracy of 0.03 ° requires support from external velocity and heading inputs. If these inputs are not connected, the error may increase to 0.1 °~0.2 ° during sharp turns.

5.2 Engineering Techniques for Improving Accuracy

External speed input: MRU 5 defaults to using its own acceleration quadratic integral to calculate heave, but centripetal acceleration during turning can contaminate the vertical channel. After connecting the velocity (VTG/VHW) from GPS or log, the algorithm can separate the centripetal acceleration component and reduce the heave drift by more than 90%.

Polling Mode: For multi beam sonar, motion data is required to be synchronized with sonar ping. Connect the sonar trigger pulse to the CMOS input line (COM3) of MRU 5 and configure it as "External Sync". MRU 5 will only output the attitude once when receiving the pulse, ensuring time alignment.