Kongsberg MRU 3 Motion Reference Unit

The heave, roll and pitch motion sensor

This 5th generation roll, pitch and heave motion sensor is

specially designed for heave compensation applications.

Typical applications

The MRU 3 model is typically used for real-time roll, pitch and

heave compensation of echosounders, fishing sonars and offshore

cranes. This sensor unit has to be mounted in a fixed mounting

direction with the connector pointing up or down.

Function

This cost-effective MRU 3 model incorporates 3-axis Micro

Electro-Mechanical-Structures (MEMS) sensors for both linear

acceleration and angular rate. This sensor unit achieves high

reliability by using solid-state sensors with no rotational or

mechanical wear-out parts.

The unit is delivered with a Windows based configuration and data

presentation software. In this software, vector arms from where the

MRU is mounted to the centre of gravity (CG) and two individually

configurable monitoring points (MPs), can be defined. The heave

measurement can be output in four different locations (the MRU

itself, CG, MP1 and MP2) simultanously on the same serial line or

Ethernet port. Typical monitoring point is the transducer head or

the crane tip.

Lever arm vectors of up to 70 metres from the sensor unit to

the location of the monitoring points (MP) can be used without

significantly degrading the sensor unit’s linear position and

velocity output accuracy.

Very high reliability is achieved by using solid-state sensors with

no moving parts and the proven MRU electrical and mechanical

construction.

Output variables

The MRU 3 outputs roll, pitch and heave together with linear

acceleration in 3-axes. The MRU 3 outputs heave position and

velocity. In addition, roll and pitch angles and corresponding

angular rate vectors are output.

PFreeHeave® algorithm

The PFreeHeave algorithm uses past measurements to output

a correct and phase-free heave from the MRU. PFreeHeave has

an advantage in long swell conditions and for applications that

can utilize a heave signal that is delayed some minutes, typically

seabed mapping applications.

External inputs

The MRU 3 accepts input of external speed and heading

information on separate serial lines or Ethernet for improved

accuracy in heave, roll and pitch during turns and accelerations.

For time synchronization the MRU accepts a 1-second time pulse

(1PPS) input on a TTL line (XIN) or as RS-232/422 signal.

Digital I/O protocols

For this 5th generation MRU data is available through both Ethernet

interface and serial lines enabling easy distribution of MRU

data to multiple users on board the vessel. Output protocols for

commonly used survey equipment are available on two individually

configurable serial lines and Ethernet/UDP.

FEATURES

• 0.010° roll and pitch dynamic accuracy

• Outputs real-time roll, pitch and heave measurements

• Outputs on RS-232. RS-422 and Ethernet

• High output data rate (200 Hz)

• Precise heave at long wave periods by use of PFreeHeave®

algorithms

• Lever arm compensation to two individually configurable

monitoring points

• Small size, light weight and low power consumption

• Each MRU delivered with Calibration Certificate

• Selectable communication protocols in the Windows based

MRU configuration software

• Export license not required

• 2-year warranty