Transport Publication TP 127 E
22.1 Each apparatus shall possess a degree of reliability in accordance with the importance of the control system of which it forms part.
22.2 The design of the control equipment shall be such that a failure in the control equipment will cause the least dangerous condition of the controlled process and such failure shall not render any reserve automatic or manual control or both inoperative.
22.3 Control and instrumentation circuits and their supply arrangements shall be so designed that failure of the power supply does not damage the installation nor endanger the ship.
22.4 The repeatability and accuracy of instruments and control equipment shall be adequate for their proposed use and shall be maintained at their specified value during their expected lifetime and normal operative use.
22.5 Electrical and electronic control equipment shall be suitable for the normal conditions encountered on shipboard.
22.6
- Control equipment shall be designed to operate satisfactorily in an air temperature range of 0° to 55° C and shall operate without deterioration in air temperature peaks of up to 70° C ;
- electrical equipment shall be designed and constructed to operate satisfactorily in locations where extreme ambient temperatures are likely to exist;
- electrical equipment to be installed inside enclosures shall be designed to operate safely due to temperature increase caused by component heat dissipation, radiation from hot machinery surfaces or from the sun.
22.7 All control equipment shall operate satisfactorily under the following conditions of relative humidity:
- 95% r.h. at temperatures up to 45° C ; and
- 70% r.h. at all other relevant temperatures.
22.8
- Control equipment shall operate satisfactorily under the following vibration conditions:
- 2.0 - 13.2 Hz , displacement amplitude ± 1.0 mm ;
- 13.2 - 80.0 Hz , acceleration amplitude ± 0.7 g , maximum acceleration .7 g;
- natural frequencies at supports for equipment and parts of equipment shall not lie within the 0 -80 Hz range, except that where they can not be kept outside this range by constructional design methods, the vibration shall be damped so that undue amplification is avoided.
22.9 Control equipment shall remain fully operational under each of the following inclinations and movements of the ship:
- inclination in all directions from the mounting position 22.5°;
- rolling 22.5°, 10 seconds full period; and
- linear vertical acceleration of ± 1.0 g .
22.10
- control equipment shall operate satisfactorily with the following variations from normal of the voltage and frequency of the ac power supplies to the equipment;
- Voltage
Permanent Variation: ±10%
Transient Variation: ± 20%
Recovery Time: 3 seconds - Frequency
Permanent Variation: ± 5%
Transient Variation: ± 10%
Recovery Time: 3 seconds
- Voltage
- ac supplied equipment shall be capable of ac maintaining functional stability and accuracy with input supplies having a possible harmonic content up to 5%;
- for battery-supplied equipment, voltage variations of +30% and -25% as determined by the charging/discharging characteristics, shall be taken into account, including ripple voltage from the charging device; and
- when the equipment is not connected to the battery during charging or when voltage stabilizing equipment is used, these values may be reduced to ± 20%.
22.11 Circuits shall be designed for easy test, calibration, maintenance and repair; repair shall preferably be effected by unit or card replacement.
22.12 The design of any circuit shall allow for variation in component data or drift within tolerances specified for the components.
22.13 The system design shall be such that there will be no undesirable mutual effect between the different circuits; a failure of one component in a circuit shall, as far as practicable, not cause failure of components in other circuits.
22.14 Design of circuits shall be such that there is no direct connection to any point of the ship’s main power supply system, e.g. isolating transformers shall be used for power supplies; the chassis shall not form part of any circuit; extensive systems shall be sub-divided and the supplies individually protected; control circuits shall be separated from signalling and indicating circuits; faults in an indicating lamp circuit shall not impair the operation of the equipment or apparatus.
22.15 Circuits which depend on the maintenance of high insulation resistance for their accurate functioning shall not be used unless special precautions are taken to maintain the high insulation resistance; such circuits shall be provided with means to check the insulation resistance.
22.16 Signal levels of ship cables shall be kept high enough to overcome the effects of contact corrosion, hum and noise pick-up.
22.17 Transducers and amplifiers shall be situated as close to each other as is practicable; to avoid possible interference on control and instrumentation cables, signal cables shall be either screened or twisted pairs and there shall be sufficient separation between signal and other cables.
22.18 Programmable Logic Controllers ( PLC’s ) shall comply with the following:
- the program and data held in the system are to be protected from corruption by loss of power;
- where any part of the program is stored in volatile memory a permanent copy of the program and the means to re-enter it are to be provided;
- the quality control procedure governing software design, development, modification, replication, and installation are to be in accordance with the most recent version of an applicable rule or code issued by a Society, Administration or a recognized Classification Society.
23. Lightning Conductors
23.1 Lightning conductors shall be fitted to each mast of all wooden and composite ships and to each mast of steel or aluminum ships having wooden masts or topmasts except where the height of any antenna exceeds that of the masts and the antenna is equipped with lightning arresters or other effective devices.
23.2 Lightning conductors shall be made of continuous copper alloy tape or cable having a cross-sectional area not less than 25 mm² (# 4 AWG ) which shall be riveted with copper rivets or fastened with copper clamps to a suitable copper spike (air terminal) not less than 13 mm in diameter, projecting at least 150 mm above the top of the mast.
23.3 Where copper tape is used, its lower end shall terminate at the point at which the shrouds leave the mast and shall be securely clamped to a copper conductor not less than 13 mm in diameter.
23.4 The copper conductor shall be led down the shrouds and shall be securely clamped to a copper plate not less than 0.2 m² in area, fixed well below the light-load waterline and attached to the ship’s side in such a manner that it is immersed under all conditions of heel and trim.
23.5 In wooden and composite ships fitted with steel masts, each mast shall be connected to a copper plate in accordance with subsection (4) and the copper rope or tape being securely attached to and in good electrical contact with the mast at or above the point at which the shrouds leave the mast.
23.6 Lightning conductors shall be run as straight as possible and sharp bends in the conductors shall be avoided; all clamps shall be of brass or copper, preferably of the serrated contact type, and shall be effectively locked.
23.7 The resistance of the lightning conductor, measured between the mast head and the position on the ground plate or hull to which the lightning conductor is grounded, shall not exceed 0.02 ohm.
23.8 Vessels in which tank vent outlets for flammable gases is located near, or at the top of a non conductive mast are to be protected by and air terminal at least 2 m above the vent outlet; on a steel mast the steel mast must extend at least 2 m above the vent outlet.