FAQs
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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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What is a Motion Reference Unit (MRU)?
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.
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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:
- Position your MRU close to the point which you’d like to measure
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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.
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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.
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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.
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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.
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The MRU calibration certificate is valid for 4 years, and full product specification is maintained in this period under normal operating conditions.
Notes:
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Yes, Norwegian Subsea Motion Reference Units (MRUs) are highly suitable for applications involving wave analysis. Our sensors provide precise measurements of motion in 6 Degrees of Freedom (6DoF), encompassing Roll, Pitch, Yaw, Surge, Sway, and crucially for wave analysis, Heave.
The high-accuracy Heave (vertical motion) data generated by our MRUs is fundamental for determining key wave characteristics such as wave height and period. Norwegian Subsea MRUs deliver a reliable Heave accuracy of 5.0 cm or 5.0%, enabling detailed analysis of sea states.