Kongsberg Seatex MRU 5 Motion Sensor

Kongsberg Seatex MRU 5 Motion Sensor – Available for rental, hire and ex-rental purchase from Ashtead Technology.

The third generation (Motion Reference Unit (MRU) 5 is specially designed for high precision monitoring measurement in marine applications and for users requiring high accuracy roll, pitch and heave measurements. The MRU 5 provides high performance motion data for various marine applications ranging from small underwater vehicles to large ship motion control. Very high reliability is achieved by using solid state sensors with no moving parts and the proven MRU electrical and mechanical construction. Ashtead Technology also have the MRU 4000m with Titanium Housing available for rent.

It is ideal for structural monitoring of offshore platforms and large vessels or any application where accurate motion data is crucial for high performance quality and safety. The MRU 5 provides documented roll and pitch dynamic accuracy of 0.03° RMS at a ±5° amplitude. The MRU 5 maintains its specified accuracy aboard any surface vessel or subsea vehicle.

Easy to Set up and Use. Interfacing the MRU 5 data output to various sonar systems is made easy since the MRU 5 software includes data protocols for more than twenty frequently used single and multibeam echosounder systems. Using the configuration cable and the Seatex MRC configuration software included with the MRU 5, a series of simple menu prompts allows the user to choose the optimum configuration for the application. The MRU 5 and the MRC software are flexible and can accommodate a wide range of application types.

Output Variables The MRU 5 offers 189 data output variables. These variables can be either digital or analogue output signals. Status messages of the MRU 5 health and overall performance can also be easily monitored by the user.

Digital I/O Protocols For two-way communication with the MRU 5, a proprietary binary serial protocol is used. Output variables are transmitted as IEEE 32 bit floats (recommended) or as scaled integers. In addition, ASCII-based NMEA 0183 proprietary sentences or various echo sounder formats may be selected as the data output protocol.

External Communication The MRU 5 accepts external input of speed and heading information on separate serial lines for improved accuracy in heave, roll and pitch during turns and accelerations. Additionally, a third CMOS input line is available for polling or synchronising the MRU data output from a peripheral computer.

The 4000-metre subsea bottle, MRU-M-SB5
This subsea bottle, made of titanium, is designed for use down to 4000 metres. The dry weight of this bottle, including the MRU, is 11.6 kg and the submerged weight including the MRU is approximately 7.4 kg. Inside the bottle, the MRU is mounted within an inner cylinder with steering plate. Correct installation and orientation of the MRU within the bottle is ensured by the design of this inner cylinder. The mounting orientation of the MRU within the bottle is indicated on the bottom cover plate. On the outside there are two mounting holes (M8) on each cover plate. The user must design his own mounting arrangement for the bottle based on these four mounting holes (M8). In addition there is a protection cap on each cover plate to protect the bottle from damage and for help during alignment. The bottle is delivered with two 8-pin Seacon connectors, one for digital communication and one for analog output channels.

Key features

  • High accuracy roll, pitch and heave measurements during turns and accelerations
  • Each MRU delivered with Calibration Certificate
  • Small size, light weight, low power consumption
  • Improved dynamic accuracy in heave, roll and pitch
  • Negligible drift in heave after vessel turn
  • High output data rate (100Hz)
  • No limitation in mounting orientation
  • Lever arm compensation when mounted off the vessel CG (centre of gravity)
  • Selectable communication protocols in the MRC software for any system using motion sensors
  • Units can be supplied for surface or subsea configuation (3000m or 4000m)


  • The MRU 5 is the ideal sensor for motion compensation of swathe bathymetric echo sounders
  • DP systems
  • ROV s helideck monitoring systems
  • high speed vessel motion damping system and towfish systems

Technical specifications

Number of Sensors3
Angular orientation rangeUnlimited
Angular Rate Range±150°/s
Axis misalignment<0.05°
Resolution in all axes<0.01°
Angular rate noise roll, pitch, yaw0.025°/s RMS
Static² accuracy roll, pitch0.25°RMS
Dynamic accuracy roll, pitch0.030° RMS
Scale factor error0.20%
Acceleration Range (all axes)±30 m/s²
Acceleration noise ²0.0020 m/s² RMS
Acceleration accuracy0.01m/s² RMS
Scale factor error0.020% RMS
Output range±50m, adjustable
Periods0 to 25s
Dynamic accuracy5 cm or 5% whichever is highest
Analog channels#4, ±10V, 14 bit resolution
Digital output variables#16 (max), RS 232 or RS 422
Data output rate (max)100Hz
Internal update rate400 Hz (angular)
Power requirements12-30V DC, max 11w
Temperature Range-5° to +55°C
Humidity range, electronicsSealed, no limit
Max vibration (operational)0.5 m/s² (10-2000 Hz continuous)
Max vibration (non-operational)20 m/s² (0-2000 Hz continuous)
Max shock (non-operational)1000 m/s² (10ms peak)
MTBF (computed)50000h
MaterialAnodised Aluminum
ConnectorSouriau 851-36RG 16-26S50


4000m subsea bottle139.2 x 357.5mm11.6 kg (in air), 7.4kg (in water)


Kongsberg MRU5 Subsea Bottlepdf39 KBDownload