1 SCOPE
1.1 A TMHD is an electronic device which uses the geomagnetic field to
obtain and transmit information about the ship’s heading.
1.2 In addition to the general requirements contained in resolution A.694(17)footnote all marine TMHD equipment should comply with the
following minimum requirements.
2 APPLICATION
2.1 A TMHD complying with the requirements contained in this
recommendation, can be used to meet the carriage requirements for a suitable device
providing heading information contained in Chapter
V of the SOLAS Convention.
2.2 In addition such THMD can meet the dynamic requirements contained in the HSC Code
chapter 13 for the carriage of a suitable device providing heading information.
3 COMPOSITION
3.1 Transmitting magnetic heading devices (TMHDs) may comprise of:
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.1 a standard magnetic compass equipped with a magnetic sensor and
electronics for generating a suitable output signal for other devices. The
compass used should be the standard magnetic compass provided under SOLAS
chapter V; or
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.2 an electromagnetic compass consisting of the sensor part and electronics
for generating a suitable output signal for other devices; or
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.3 any type as defined under .1 and .2 additionally equipped with a rate gyro
to improve dynamic performance.
4 CONSTRUCTION
4.1 Fore-and-aft mark
4.1.1 A fore-and-aft mark should be inscribed on the magnetic sensor
housing, which should be installed in parallel to the ship’s fore-and-aft line.
4.1.2 The accuracy of the fore-and-aft mark should be within ± 0.5° to
the fore-and-aft direction of the housing.
4.1.3 If a rate gyro is installed it should be marked in the same way and
additionally be marked with top or bottom.
4.2 Fitting
4.2.1 Provision should be made, in the mounting arrangements of the
magnetic sensor, for correction of any misalignment, up to ± 5°, with respect to the
fore-and-aft line.
4.2.2 The fitting of the sensor arrangement to the compass in paragraph 3.1 above
should still enable the compass to comply with resolution A.382(X) with particular
reference to accuracy, gimbling and use of the azimuth reading device.
4.3 Compensation of deviation and heeling error
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Provision should be made to correct the deviation and heeling error and it
should be possible to correct the following values:footnote
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.1 vertical component of the ship's magnetic field (producing the
heeling error): up to ±75 μT;
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.2 coefficient A: up to ±3°;
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.3 coefficient B: up to ±(720/H)°;
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.4 coefficient C: up to ±(720/H)°;
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.5 coefficient D: up to ±7°; and
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.6 coefficient E: up to ± 3°,
where H is the horizontal component of the geomagnetic flux density in microteslas
(μT).
4.3.1 Indication of compensation
4.3.2 Protection of compensation
4.4 Heading output
4.5 Interfaces
5 PERFORMANCE
5.1 Accuracy of heading
5.1.1 Static
5.1.2 Dynamic
5.2 Follow-up accuracy of the transmission system
The follow-up accuracy of the transmission system should be within ±
1.5°, when the sensor is
rotated at a rate of 20°/s.
6 ELECTROMAGNETIC COMPATIBILITY
The compass system, with regard to electromagnetic interference and immunity, should,
in addition
to resolution A.694(17), comply with resolution A.813(19).footnote
7 FAILURE CONDITIONS
An alarm should be provided to indicate a failure of the power supply to the compass
system.