What is the difference between an MRU and an IMU?
While both Motion Reference Units (MRUs) and Inertial Measurement Units (IMUs) measure motion, they differ significantly in their processing and output. An IMU typically consists of accelerometers and gyroscopes that provide raw acceleration and angular rate data. IMUs only provide raw data from their sensors and do not include "smart" features such as processing (e.g., Kalman Filter). The IMU cannot provide attitude (roll and pitch), velocity, or position without external processing.
A Norwegian Subsea MRU, on the other hand, is a more sophisticated system. It utilizes data from internal MEMS-based accelerometers and gyroscopes, similar to an IMU, but integrates this data using advanced sensor fusion algorithms. These algorithms process the raw sensor readings to compute and output highly accurate, real-time measurements of orientation (Roll, Pitch, Yaw) and motion (Heave, Surge, Sway) in 6 Degrees of Freedom (6DoF).
Our MRUs are specifically designed, calibrated, and rigorously tested for the demanding conditions of marine, offshore, and subsea environments. They provide stabilized, reliable, and application-ready motion data crucial for tasks like dynamic positioning, heave compensation, hydrographic surveying, and more. Unlike basic IMUs, Norwegian Subsea MRUs deliver processed, high-accuracy motion information tailored for direct use in control and monitoring systems, often without needing recalibration during their operational life.
Related products
Usage area
IP 65
Connectors
RJ45 or RJ50
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
50 m depth, IP 68
Connectors
Lemo or SubConn 8 or SubConn 16
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
6000 m depth
Connectors
SubConn 8
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
Hazardous areas
Connectors
Pigtail cable
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Further reading
Advanced motion compensation for sonars introduced at Ocean Business 2025
MRUs for vessel performance optimisation in focus at Europort 2025
Research Project to Test Value of MRU Data for Vessel Performance and Carbon Reduction
Related questions
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What is the difference between the MRU Marine and MRU Marine SW?
- The MRU Marine has an IP-68 rating, uses a Lemo 16-pin connector and has indicator lights.
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When navigating the complexities of motion sensing and navigation systems, it is essential to understand the distinctions between devices and systems like Inertial Measurement Units (IMUs), Inclinometers, Roll & Pitch sensors, Vertical Reference Units (VRU), Attitude and Heading Reference Systems (AHRS), Motion Reference Units (MRUs), Gyrocompasses, and GNSS-Aided Inertial Navigation Systems (GNSS/INS). Each serves specific purposes and offers different levels of functionality, accuracy, and application scope.
Gyrocompass
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The MRU Compact uses a standard RJ45 ethernet cable where power is supplied through Passive PoE (Power over Ethernet). In most cases you cannot connect the MRU directly to a an ethernet switch with PoE, since most of these are Active PoE.
We normally supply your first MRU Compact with a start kit containing a POE RJ45 spliter socket. You will only need standard RJ45 cat5 ethernet cables to connect the MRU to the spliter socket and the spliter socket to your PC or ethernet switch.
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