1 SCOPE
1.1 A transmitting heading device (THD) is an electronic device, which provides
information about the ship’s true heading.
1.2 In addition to the general requirements contained in resolution A.694(17)footnote and the relevant standard for the sensing part used, the
THD equipment should comply with the following minimum requirements.
1.3 Where the IMO performance standards which apply to the sensing part do not specify a
geographical operating area the THD should operate from 70º latitude south to 70º
latitude north as minimum.
2 APPLICATION
2.1 The THDs complying with the requirements contained in this recommendation can be used
for heading information as contained in chapter V of the SOLAS Convention.
2.2 In addition such THD should meet the dynamic requirements contained in the HSC Code,
chapter 13 for the carriage of a suitable device providing heading information.
3 DEFINITION
3.1 Heading: for the purpose of these standards any ship’s heading to be input to
the THD function.
3.2 Sensing part: a sensing function of detecting any heading information
connected to the transmitting device.
3.3 Transmitting part: device which receives a heading information from the
sensing part and convert to the required accurate signal.
3.4 True heading: horizontal angle between the vertical plane passing through the
true meridian and the vertical plane passing a through the craft’s fore and aft datum
line. It is measured from true north (000º) clockwise through 360º.
3.5 Transmission and resolution error: error which is caused by the method used to
transmit the original information to a receiving device. Such method may have a limited
capability to code any possible value of the information e.g. step output with 1/6º
resolution. This error is caused by the method used inside the THD and at its output to
code the information.
3.6 Static error: error which is caused by any reason and which stays unchanged in
value during the operation of the system. This error should be measured under static
conditions.
3.7 Dynamic error: error which is caused by dynamic influences acting on the
system such as vibration, roll, pitch or linear acceleration. This error may have an
amplitude and usually a frequency related to the environmental influences and the
parameters of the system itself.
3.8 Follow-up error: error which is caused by the delay between the existence of a
value to be sensed and the availability of the corresponding signal or data stream at
the output of the system. This error is e.g. the difference between the real heading of
turning vessel and the available information at the output of the system. The follow-up
error disappears when the system is static.
4 OPERATIONAL REQUIREMENT
4.1 Functionality
4.1.1 The THD receives a heading signal and generates a suitable output signal for other
devices.
4.1.2 Any sensor part may be included in the device.
4.1.3 Any correcting devices or parameters should be protected against inadvertent
operation.
4.2 Presentation of information
4.2.1 All displays with the exception of the sensor, and all outputs of heading should
indicate true heading.
4.2.2 Manually settable values used for electronic correction should be indicatable by
adequate means.
4.3 Accuracy
4.3.1 The THD should be tested for accuracy with the sensing part connected. If the
sensing part is so designed that it is included in the transmitting part, the equipment
should be tested together with all parts.
4.3.2 The THD should meet at least the following accuracy at the output of the device
under sea conditions as specified in resolution A.424(XI) or A.821(19) as applicable:
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.1 Transmission and resolution errors. The transmission error including the
resolution error should be less than ±0.2º;
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.2 Static errors. The static error should be less than ±1.0º;
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.3 Dynamic errors.footnote The dynamic error amplitude should be less than
±1.5º. The dynamic error frequency should be less than 0.033Hz equivalent to a
period not shorter than 30s if the amplitude of the dynamic error exceeds ±0.5º;
and
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.4 Follow-up errors: The follow-up error for different rates of turn should
be:
4.4 Interfacing
At least one output should be in accordance with the relevant international marine
interface standard.footnote
5 ELECTROMAGNETIC COMPATIBILITY
The device, with regard to electromagnetic interference and immunity, should, in addition
to resolution A.694(17),footnote comply with resolution A.813(19).footnote
6 FAILURE CONDITIONS
An alarm should be provided to indicate malfunctions of the THD or a failure of the power
supply.