BS MA 2-1:1985 pdf free download.Magnetic compasses and binnacles Part 1: Specification for class A magnetic compasses, their binnacles and azimuth reading devices (including test procedures).
1.1 Scope
This Part of BS MA 2 specifies requirements for class A magnetic compasses, their binnacles and azimuth reading devices.
NOTE The title of the publication referred to in BS MA 2-1 is given on the inside back cover.
1.2 Definitions
For the purposes of this Part of BS MA 2, the
definitions given in BS MA 2-4 apply.
1.3 Test certificates
1.3.1 Type testing shall be carried out before the instruments specified enter regular service. All tests, except those identified as type tests only, apply to individual testing.
New devices only are accepted by type testing. All compasses other than those compasses, without gimbals, which are used as steering compasses only, are to be tested complete with their gimbal rings and outer gimbal bearings.
1.3.2 Devices that have passed type or individual tests and comply with the requirements shall be so certified.
1.3.3 Each type test certificate is valid exclusively for the model tested. In case of alterations or technical improvements, which affect its compliance with this Part of BS MA 2, the model shall be given a new identification number or mark and the type test repeated. All alterations shall be submitted to the original test authority who will decide whether a new type test is necessary (see Appendix A, Appendix B and Appendix C).
1.3.4 Copies of the certificate shall be issued on demand; they shall be explicitly marked “copy”.
Section 2. Compasses, bowls and gimbals
2.1 General
2.1.1 Temperature conditions for testing Testing shall be carried out on all class A magnetic compasses, with or without transmitting system, at a temperature of 20 ± 3 °C, except for the high and low temperature tests (see 2.2.2 and 2.2.3).
The order in which tests are carried out is at the discretion of the testing authority except that 2.2.1, 2.2.2 and 2.2.3 shall be performed first and in that order.
Depending on the construction of the azimuth reading device, the axis of rotation shall be defined by an indentation or centre boss on the top glass cover of the compass, or by the centre of the inside or outside of the verge ring, or by the outside rim of the compass bowl.
2.4.3.2 Method of test (type test only). The examination is carried out by measuring on a compass testing stand the displacement that is necessary to bring the pivot point of the compass, when horizontal, and the axis of rotation of the azimuth reading device, one after the other into coincidence with the axis of rotation of the testing stand.
2.5 Compass card bearing
2.5.1 Height of the pivot bearing
2.5.1.1 Requirement. The pivot point shall not deviate from the horizontal plane through the inner gimbal axis by more than 1 mm. If the pivot bearing is equipped with a vertical spring suspension, this condition shall be fulfilled when the directional system is completely immersed.
2.5.1.2 Method of test (type test only). When the compass bowl is opened, this examination is carried out using a depth gauge, the rim of the compass being the plane of reference.
2.5.2 Retention of the directional system against displacement
The mounting of the directional system in the compass bowl shall be constructed in such a manner that it returns to the original position on its pivot when the bowl is inverted and then returned to its normal position.
2.5.3 Freedom of tilt of the directional system
2.5.3.1 Requirement. The directional system and the compass bowl shall be constructed in such a manner that the directional system shall rotate freely when the compass bowl is tilted in any direction at an angle of:
a) 100 when the compass bowl has an external gimbal system;
b) 30° in other cases.
2.5.3.2 Method of test. The examination is carried out using a revolving platform with adjustable inclination.
2.7.4 Period
2.7.4.1 General. Compasses shall be subjected to either 2.7.4.3 a) or 2.7.4.3 b).
2.7.4.2 Requirement. For periodic compasses, the mean time (in s) taken between the first and second passing of the original heading shall be not less than /(2 600/H).
NOTE Throughout this standard H is measured in microteslas (pT).
For heavily damped or aperiodic compasses, the mean time (in s) taken to return finally to within 1° of the magnetic meridian shall be not more than %J(57 600/H).
2.7.4.3 Method of test. The tests are carried out as follows.
a) Test A (periodic compasses,). The card is deflected 40° from the magnetic meridian and held there for at least 10 s. It is then released and the time taken between the first and second passing of the original heading is noted.
This test is repeated on the other side of the meridian and the mean is taken.
b) Test B (heavily damped or aperiodic compasses). The card is deflected through 90°, held there for at least 10 s and then released and the time taken between the first and second passing of the original heading is noted. This test is repeated on the other side of the meridian and the mean is taken.
2.8 Accuracy
2.8.1 Directional error
2.8.1.1 Requirement. The directional error shall not exceed 0.5° on any compass heading.
2.8.1.2 Method of test. The examination is carried out on a compass testing stand. After bringing the centre of rotation of the compass card into the axis of rotation of the testing stand, the directional error is read at the card graduation by means of a telescope, when the vertical plane of the sight passing through the axis of rotation has been aligned with the magnetic meridian in advance. This measurement is carried out on at least four equidistant headings. On measuring, the top glass is tapped gently to eliminate the error due to friction (see 2.8.3).
NOTE Where the test is undertaken in the compass bowl, it should be noted that the resulting value then includes the deviation due to any magnetic material in the compass and)or in the fluxgate.
4.2.3 Provisions to correct misalignment
4.2.3.1 Requirement. Fore and aft marks provided on hinnacles shall be in the same vertical plane to within 0.5° as the axis of the fore and aft gimbal bearings.
In type Al binnacles provisions shall be made for any misalignment in respect of the fore and aft line of the ship by turning the binnacle through an angle of not less than 4° and not more than 6°.
NOTE This requirement is not obligatory for type A2 binnacles.
4.2.3.2 Method of test. The examination is carried out with the aid of a plumb line and with the compass in the binnacle.
4.2.4 Correcting devices, marking, coercivity and securing
4.2.4.1 Corrector magnets
4.2.4.1.1 Requirement. Corrector magnets shall be marked red at the North seeking end and shall have a coercivity of not less than 11 200 AIm.
All fittings carrying correction devices shall be securely fixed to the binnacle and well protected against sea and weather.
Devices (for instance a scale) to indicate the position of the correcting devices at any given time shall be provided. Holes or grooves used for horizontal corrector magnets shall be numbered and the numbers shall read from the bottom upwards.
Provisions shall be made to protect the correcting devices of the binnacles from unauthorized access and unintentional displacement.
4.2.4.1.2 Method of test. The examination is carried out visually.
4.2.4.2 Heeling error corrector magnets
4.2.4.2.1 Requirement. Heeling magnets shall be capable of producing a vertical flux density over the range — 75 iT to + 75 pT at the magnets of the directional system.
The tube provided for one or more heeling error magnets to correct the influence of vertical magnetism shall be fitted centrally below the compass bowl in the vertical axis of the binnacle. When several heeling error magnets are provided for, the casings shall be constructed so that the magnets can be placed in a symmetrical arrangement about its axis. The heeling error magnets and their holders shall be capable of being securely fixed in position. Provision shall be made so that the distance between the upper end of the correcting magnets and the magnets of the directional system shall be not less than twice the length of the correcting magnets in type Al binnacles.