Motion Reference Unit (MRU) for Heave Compensation

Product Specifications

Technical details and manufacturing context for Motion Reference Unit (MRU)

Definition

The Motion Reference Unit (MRU) is a critical component within a Heave Compensation System that precisely measures the vessel's motion in six degrees of freedom (surge, sway, heave, roll, pitch, yaw). It provides the essential real-time motion data that the compensation controller uses to calculate and command counter-movements to stabilize a load or equipment, thereby isolating it from the vessel's motion. The MRU typically contains a combination of high-precision accelerometers and gyroscopes (often in an Inertial Measurement Unit - IMU) and sometimes GNSS receivers. It measures linear accelerations and angular rates. These raw measurements are processed through sensor fusion algorithms (e.g., Kalman filters) to compute the vessel's precise orientation (attitude: roll, pitch, heading) and translational motion (heave, surge, sway). This processed motion data is output in real-time to the heave compensation controller. The unit is designed for marine environments, with a protective housing of aluminum alloy or stainless steel. Key parameters include a roll/pitch measurement range of ±45°, heave range of ±30 m, angular accuracy of 0.01° RMS, heave accuracy of 5 cm RMS for periods 3-20 s, and an update rate configurable up to 200 Hz. It operates on 24 V DC (±10%) with typical power consumption of 15 W, and is protected to IP67. Interfaces include RS-422 and Ethernet (NMEA 0183 and TCP/IP). The unit weighs 5.5 kg without cable and has dimensions of 250×180×120 mm. Operating temperature range is -40 to 85 °C per IEC 60068-2-1/2. Always verify model-specific values and standards with the legal manufacturer or supplier.

Working Principle

The MRU uses accelerometers and gyroscopes to measure linear accelerations and angular rates. These raw signals are fused using algorithms like Kalman filters to compute the vessel's attitude (roll, pitch, heading) and translational motion (heave, surge, sway). The processed data is output in real-time to the heave compensation controller, which calculates counter-movements to stabilize loads. The unit may also integrate GNSS for enhanced positioning. The sensor fusion compensates for sensor errors and dynamic conditions, providing accurate motion reference for compensation systems.

Common Materials

Electronic components (ICs, PCBs), MEMS sensors, Protective housing (aluminum alloy or stainless steel)

Technical Parameters

Parameter	Typical range	Notes & selection driver
Measurement Range (Roll/Pitch)	±45 °	Full range for typical marine applications
Heave Measurement Range	±30 m	For open sea conditions
Angular Accuracy (Roll/Pitch)	0.01 °	RMS at static conditions
Heave Accuracy	5 cm	RMS for periods 3-20 s
Update Rate	100 Hz	Configurable up to 200 Hz
Supply Voltage	24 ±10% V DC	Reverse polarity protected
Power Consumption	15 W	Typical at 24 V DC
Operating Temperature	-40–85 °C	Storage and operationIEC 60068-2-1/2
Ingress Protection	IP67	Waterproof for deck installationIEC 60529
Interface	RS-422, Ethernet	NMEA 0183 and TCP/IP outputIEC 61162-1
Weight	5.5 kg	Without cable
Dimensions (L×W×H)	250×180×120 mm	Compact enclosure

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM

Inertial Measurement Unit (IMU)
Contains accelerometers and gyroscopes to measure raw linear acceleration and angular rate.

Material: Silicon (MEMS), electronic components
Processing Unit
Runs sensor fusion and filtering algorithms to compute precise attitude and motion from raw IMU data.

Material: Electronic components (processor, memory)
Communication Interface
Outputs the processed motion data (e.g., via serial, Ethernet) to the heave compensation controller.

Material: Electronic components (transceivers, connectors)
Housing Part
Protects the internal electronics from environmental factors (water, dust, shock).

Material: Aluminum alloy or stainless steel

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Motion Reference Unit (MRU).

Applied To / Applications

This component is essential for the following industrial systems and equipment:

Heave Compensation System

View system integration details

Manufacturers of Motion Reference Unit (MRU)

Manufacturer profiles associated with Motion Reference Unit (MRU).

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Frequently Asked Questions

What is the primary function of an MRU?

The MRU measures the motion of a vessel or platform in six degrees of freedom and provides real-time data to a heave compensation controller, which uses it to stabilize loads or equipment.

What are the typical measurement ranges for roll/pitch and heave?

For typical marine applications, the roll/pitch measurement range is ±45°, and the heave measurement range is ±30 m for open sea conditions. These values are reference ranges and should be confirmed for the specific model.

What interfaces does the MRU typically support?

The MRU typically supports RS-422 and Ethernet interfaces, with output formats including NMEA 0183 and TCP/IP. These are standard for integration with compensation systems.

What environmental protection does the MRU have?

The MRU is rated IP67 for waterproof protection, suitable for deck installation. It operates in temperatures from -40 to 85 °C, per IEC 60068-2-1/2. Always verify with the manufacturer for specific models.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records.

Preliminary Technical Classification

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pressure:	0 to 10 bar absolute
other spec:	Heave accuracy: ±0.05m or 5% of motion (whichever is greater), Pitch/Roll accuracy: ±0.1°, Update rate: 100 Hz
temperature:	-40°C to +85°C

Motion Reference Unit (MRU)

Product Specifications

Industry Taxonomies & Aliases

Applied To / Applications

Industrial Ecosystem & Supply Chain Structure

Application Fit & Sizing Matrix

Reliability & Engineering Risk Analysis

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