The three values of settle point heading so obtained shall be recorded and the difference between any two shall not exceed O,35°× secant latitude.
NOTE If this test follows that described in 6.3, then the "settle" obtained in 6.3 may be used as the first value required by this repeatability test provided that the second "settle" follows a switch off period of not less than 12 h and not more than 7 days.
6.5 Settling time on a Scorsby table
The master compass shall be mounted on a Scorsby table with the master compass fore and aft line nominally parallel with one axis of the table which shall be designated the roll axis.
The other nominally horizontal axis at right angles to the first shall be designated the pitch axis.
The system shall then be switched on in accordance with the manufacturer's instructions with the following nominal simple harmonic table motions:
- roll axis: Peak amplitude 5°±1°, period 15 s ±1 s;
- pitch axis: Peak amplitude 5°±1°, period 6 s ±1 s;
The settling time as defined in 3.10 shall conform to the requirements specified in 5.3.1.
NOTE THD readings to determine the settle condition may be taken with the Scorsby table stationary and nominally level, and with a minimum delay before resuming the specified table motion.
6.6 Scorsby test
The master compass shall be settled on the Scorsby table with the table stationary, nominally level and its roll axis aligned North-South within ±1°.
The compass fore and aft mark shall be aligned to within ±1°of the table roll axis. The following nominal simple harmonic motions shall be applied simultaneously to the three axes of the table for 25 min:
- roll axis: Peak amplitude 20°±2°, period 6 s ±1 s;
- pitch axis: Peak amplitude 10°±2°, period 10 s ±1 s;
- yaw axis: Peak amplitude 5°±1°: 1°, period 15 s ±1 s;
At the end of 25 min, the table motion shall be stopped, the table returned to its original position and the THD heading recorded without delay.
This test shall be repeated with the roll axis of the motion table aligned at 045°±1°, at 090°±1° and at 315°±1°. At each of these headings, the compass settle point shall be determined before commencing the table motion and any change of heading indication by the compass between the settle point heading immediately prior to the motion and the heading at the conclusion of the motion shall be recorded as error due to motion.
In each of the four tests, error due to the motion shall be less than ±1,5°× secant latitude.
Any horizontal accelerations applied during this test shall not exceed 1 m/s2.
6.7 Intercardinal motion test
The master compass shall be securely mounted on a device having the ability to move with nominal simple harmonic motion such that the component of motion in a horizontal plane shall have a peak acceleration of 1,0 m/s2 ±0,1 m/s2. The direction of motion of the device in the horizontal plane shall be an intercardinal direction to within ±3°.
When so mounted, the master compass shall be settled (see 3.10) and the settle point heading shall be obtained (see 3.11) with the device stationary and nominally leveled The device shall then be submitted to the motion previously described having a peak acceleration of 1,0 m/s2 ±O,1 m/s2 with a periodic time of not less than 3 s, for a duration of 2 h. Any difference between the THD heading recorded during the motion and the settle point heading prior to the motion will be considered as due to the motion; it shall not exceed 1,5°× secant latitude.
NOTE The THD heading recorded during the motion should discount any modulation at frequencies equal to or higher than the frequency of the applied motion.
6.8 Output accuracy test
6.8.1 The master compass on a level rotary table shall be turned at a rate not greater than 10°/s, to read data both of THD output and angle of the table at least 5°intervals during this test.
The maximum follow-up errors shall conform to the requirements specified in 5.3.4.
