What is the difference between MEMS-based and FOG-based MRUs?
Motion Reference Units (MRUs) primarily differ based on the type of gyroscope technology they employ. Norwegian Subsea utilizes advanced Micro-Electro-Mechanical Systems (MEMS) technology in all our MRUs.
MEMS sensors are solid-state devices manufactured using techniques similar to those for integrated circuits. This results in sensors that are inherently compact, lightweight, highly robust, and significantly more cost-effective than older technologies. They offer excellent reliability and low power consumption. Our engineers combine state-of-the-art MEMS sensors with sophisticated sensor fusion algorithms to achieve high accuracy and performance, validated in real-world sea conditions.
Fiber Optic Gyroscope (FOG) technology, conversely, uses the interference of light passing through a coil of optical fiber to measure rotation. While capable of high performance, FOG-based MRUs are typically larger, heavier, significantly more expensive, and can be more sensitive to shock and vibration compared to MEMS units. Historically, FOGs were often required for the highest accuracy applications, but advancements in MEMS technology and algorithms have closed this gap considerably.
The most advanced and expensive Fiber Optic Gyroscope (FOG) navigational instrument can determines true north. Unlike magnetic compasses, which are susceptible to magnetic anomalies, these instruments identifies true north based on the Earth's rotation, aligning with the geographic North Pole. It provides constant and reliable heading information without dependence on external signals like GPS, which can be disrupted or unavailable. These instruments has a settling time to stabilize and accurately align with true north after initialization, which can vary depending on the system's design and environmental factors. At high northern or southern latitudes, the gyrocompass faces challenges due to the diminishing horizontal component of Earth's rotation, making it harder to align to true north.
For the vast majority of marine, subsea, and offshore applications, modern MEMS-based MRUs like those from Norwegian Subsea provide exceptional performance (with Roll/Pitch accuracies from ±0.05° down to ±0.01°) that meets or exceeds operational requirements. They represent a superior value proposition, offering high accuracy, proven reliability, ease of integration, and significantly lower total cost of ownership compared to FOG-based systems, often without the need for recalibration.
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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