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|  MIL-S-85018A(AS)
3.5.1.2.2 Heading Drift - The maximum free drift in Heading with the system
in the DG mode shall not exceed plus or minus 1.0 degree per hour where the -
earth's rate and drift bias are electrically compensated.
3.5.1.2.3 Drift Correction - The system shall contain earth rate and drift
bias compensation for Directional Gyro drift. Drift bias shall have a range of
plus or minus 4.5 degrees/hour and shall have an accuracy of plus or minus .2
degree/hour. Earth rate compensation shall be 15 degrees per hour times the
sine of the latitude and shall have an accuracy of plus or minus .3 degree per
hour.
3.5.1.2.4 Manual Slewing - Operation of the Set Heading control on the
Controller shall allow slewing of the heading outputs at varying rates to 30
degrees per second. Settable accuracy shall be within plus or minus .1 degree.
3.5.1.2.5 Following-Up Rate. The heading outputs shall be capable of
continuously following a heading input at a rate of 300 degrees per second.
3.5.1.3 SLAVED Mode Performance -
3.5.1.3.1 Heading Accuracy - The static and dynamic accuracy of the heading
outputs after proper adjustment of the index, one cycle and two cycle compensa-
tion adjustments shall be as specified in 3.4.2.
3.5.1.3.2 Slaving Characteristics - The slaving rate of the heading loop
shall be 1.5 degrees per minute per degree of synchronization error, up to a
maximum slaving rate of plus or minus 2.5 plus or minus .2 degree per minute as
specified in Figure 3. The synchronization error shall be filtered with a time
constant of 5 plus or minus 1 second.
3.5.1.3.3 Slaving Cutoff
3.5.1.3.3.1 Turn Rate Cutoff - A solid state azimuth rate sensor shall be
provided to permit control of heading slaving during turns. Under standard
conditions, slaving cutoff shall occur for the following azimuth inputs:
a. Slaving shall be removed during turns of plus or minus 8
degrees, plus or minus 30 degrees, and plus or minus 180 degrees per minute
within 30, 11, and 8 seconds respectively, and shall be returned within 20
seconds after the rates have ceased. Turn rate cutoff shall not be commanded by
turns of plus or minus 3 degrees per minute or less.
b. Slaving shall be removed within 30 seconds when an input of
30 degrees per minute rate of turn is superimposed on a plus or minus .8 degree,
one cycle per second azimuth oscillation. Slaving shall remain cutoff until the
30 degree per minute rate of turn has ceased.
c. Turn rate cutoff shall not be commanded by the following
azimuth oscillations:
(i) plus or minus .8 degree with a 1.0 second period.
(ii) plus or minus 1.5 degrees with an 8.0 second period.
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