An optical gyrocompass is based on the high-performance fiber optic gyroscope's sensitivity to the earth's rotation rate. The advantage over conventional gyrocompasses is that it starts up quickly and should also have a long operating life. An optical gyrocompass is developed with a north-seeking accuracy of 0.05 degrees.
P F M ) c o m p o n e n t s . I n t h i s p a p e r we p r e s e n t a n e x p e r i m e n t a l i n v e s t i g a t i o n o n n o r t h -s e e k i n g a c c u r a c y b y c o n s i d e r i n g t h e r a t e r e s o l u t i o n o f t h e FOG. 2. P R I N C I P L E F i g u r e 1 s h o w s a n e x a m p l e f r o m t h e e a r t h ' s r o t a t i o n d e t e c t i o n r e s u l t . I n t h e e x p e r i m e n t . t h e f i b e r s e n s i n g c o i l i s p l a c e d p e r p e n d i c u l a r t o t h e h o r i z o n . a n d r o t a t e d v e r t i c a l l y i n m a n y d i r e c t i o n s . W h e n t h e l o o p p o i n t e d d i r e c t l y n o r t h , t h e o u t p u t o f t h e FOG d e c r e a s e d t o n e a r l y z e r o . T h u s a h i g h l y s e n s i t i v e g y r o s c o p e c a n b e u s e d a s a d e o d e s i c c o m p a s s . I n a n i d e a l c a s e , t h e r e q u i r e d r a t e r e s o l u t i o n 6 0 o f t h e d i r e c t i o n s e n s o r i s g i v e n a s f o l l o w s . 6 n = a O . ( n e c o s O l ) / ( l 8 0 / n ) ( d e g / h ) ( 1 ) w h e r e n e i s t h e e a r t h ' s r o t a t i o n r a t e . a n d 0 I i s t h e l a t i t u d e . F o r e x a m p l e , w h e n 9 I i s 3 7 d e g r e e s . a n d 6 8 i s 0. 5 d e g r e e s t h e n 6'0 i s 0. 1 d e g / h . p r o t o t y p e . T h i s i n s t r u m e n t c o n s i s t s o f t h r e e p a r t s : FOG, h o r i z o n t a l l e v e l s t a b i l i z e r , a n d t h e r o t a t i n g m e c h a n i s m . F i g u r e 5 s h o w s o n e o f t h e e x p e r i m e n t a l r e s u l t s . I n t h i s e x p e r i m e n t , t h e e a r t h ' s r o t a t i o n r a t e w a s m e a s u r e d e v e r y 3 6 d e g r e e s . F i g u r e 6 s h o w s t h e a c c u r a c y o f t h e d i r e c t i o n s e n s e o r , w h e r e t h e e a r t h ' s r o t a t i o n r a t e w a s m e a s u r e d e v e r y 3 6 d e g r e e s . A c c o r d i n g t o t h i s e x p e r i m e n t , t h e n o r t h -s e e k i n g s e n s i t i v i t y o f a b o u t 0 . 5 d e g r e e s a g r e e s w e l l w i t h E q n ( l ) , c o n s i d e r i n g t h a t t h e r a t e r e s o l u t i o n o f t h e FOG i s a b o u t 0 . 1 d e g r e e s p e r h o u r a t a n i n t e g r a t i o n t i m e o f 5 s e c o n d s .
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