FAQs
Find the answer to your question here, or contact us at sales@norwegian-subsea.no.
Find the answer to your question here, or contact us at sales@norwegian-subsea.no.
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.
The MRU Compact is also available with a RJ50 connector instead of the standard RJ45 Ethernet connector.
The RJ50 connector (also called 10P10C connector) is identical in shape to the RJ45 connector but has 10 wires. The outside 2 pins on a RJ45 connector are blind but these are in use for the RJ50 connector.
Choosing the right motion sensor ensures optimal performance and reliability for your specific needs. At Norwegian Subsea, we offer a range of high-performance Motion Reference Units (MRUs) designed for diverse marine, subsea, and offshore applications. The selection process primarily depends on the operational environment, required accuracy, connectivity needs, and specific functionality.
First, consider the installation environment. Our MRU Compact (IP65) is ideal for indoor or control box mounting, featuring easy plug-and-play installation with passive Power over Ethernet (PoE) via an RJ45 connector. For on-deck or shallow subsea applications (up to 50m), the MRU Marine (IP68) provides robust performance with versatile connectivity options including Ethernet, RS-232/485, and PPS. For deep-water applications up to 6000m, the MRU Subsea offers a compact, high-pressure titanium housing with Subconn connectors. If operating in hazardous areas, the MRU Ex provides a certified stainless steel solution (II 2 G Ex d IIC Gb).
Motion Reference Unit (MRU)
Definition: A motion Reference Unit (MRU) is a specialized device and self-contained sensor that measures motion in all six degrees of freedom (DoF): Roll, Pitch, Yaw, Surge, Sway and Heave. The six DoF positions, velocities and accelerations are measured by the MRU using high-end gyroscopes and accelerometers (and sometimes magnetometers) together with advanced fusion algorithms. An MRU has high accuracy Roll and Pitch measurements, and measures oscillatory Heave, Surge and Sway motions for wave periods at sea. Linear motions with very long periods, or steps, cannot be measured by an MRU as it assumes a 0 mean heave position.
A motion Reference Unit (MRU) is a device that measures motion in all six degrees of freedom (DoF): roll, pitch, yaw & surge, sway and heave. The six DoF positions, velocities and accelerations are measured by the MRU using high-end gyroscopes and accelerometers (and sometimes magnetometers) and processed by advanced sensor fusion algorithms.
Your MRU can be mounted almost anywhere on your vessel and in any orientation, but there are some guidelines you can follow to ensure the absolute highest accuracy of measurements from your device:
Yes, the MRU can output heave measurements, including position, velocity and acceleration at 2 remote monitoring points.
In addition, you can use the measurment point at the centre of gravity and select the CoG position as the position of your 3rd monitoring point. Note: CoG position is not used as part of the calculations and can be set to any position.
The MRU Marine uses a custom 16-wire cable with Lemo connectors.
The 16 wires provide full flexibility for both Ethernet, RS-232, RS-485, PPS time sync and Aiding input.
Yes, our MRUs measure surge and sway.
But note that as for heave, the measurements are about a zero mean average position. This means that for a ship that moved forward, it’s only the high frequency part of the surge motion that is measured by the MRU.
Yes, the MRU outputs accelerations as well as velocities. You can configure the MRU to output acceleration and velocity data in the MRU, Vessel or NED frame. Both raw and lowpass filtered accelerations are available.
The MRU calibration certificate is valid for 4 years, and full product specification is maintained in this period under normal operating conditions.
Notes:
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
The MRU (Motion Reference Unit) monitors vessel motions to evaluate risks related to sloshing and structural fatigue in cargo containment systems. It supports a condition-based inspection regime under DNV’s Alternative Survey Programme (ASP).
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.
Inclinometer