Fiber Optic Gyroscopes. Instrumentation: Sensors and Signals

Transcription

1 Fiber Optic Gyroscopes Instrumentation: Sensors and Signals

2 History Developed in the 1980s as an alternative to Laser Ring Gyroscopes. More compact Less sensitive

3 Comparison and applications

4 WHOI Puma

5 How does a RLG work? Based on the Sagnac effect, like the FOG

6 Basic FOG configuration

7 Classical explanation Basics Variation in wave vector Wave vector Phase shift Δk = k v c v = Ω r dφ = Δk ds

8 Classical explanation Phase difference dφ = Ω r ds k c Using Geometry dφ = k c ΩcosΨrsinχds

9 Classical explanation Integrating phase difference along the path length rsinχ ds = 2AN Δφ = k c ΩcosΨ2AN

10 FOG Equation Δφ = k c ΩcosΨ2AN φ s = 2Δφ k = 2π/λ Ω p = Ω cos Ψ φ s = 8πANΩ p λc Angular wavenumber

11 Relativistic Explanation Δf = 2Ω p R λ φ s 2π = Δf 2πR c φ s = 8πAΩ p * λc *Only correct if the detector is moving with the gyroscope

12 Open loop configuration with phase modulation

13 Analog signal implementation

14 Analog circuit implementation I = 1 + J I 0 Φ m + 2 J 2k 0 k 1 Φ m cos2kω m t cosφ s + 2 J 2k 1 k 1 Φ m cos (2k 1)ω m t sinφ s Issues: Fluctuations in offset voltages lower bias stability. Detectable angular velocity is limited to ± π 2 rad Linearity and scale factor stability are easily deteriorated by fluctuations in photodetector intensity.

15 Signal Processing Used

16 Digital circuit implementation Digital signal processing apparatus. First to forth heterodyne mixers (2, 3, 4 and 5), an ADC (6), a timing pulse generating unit (7), a cosine/sine signal generating unit (8), first and second digital multipliers (9, 10), first and second digital filters (11, 12), a quadrant discriminating unit (13), an angular velocity computing unit (15), a phase modulation index computing unit (14) and a reference signal generating circuit (1).

17 Digital circuit implementation Isolate different harmonics Digital signal processing apparatus. First to forth heterodyne mixers (2, 3, 4 and 5), an ADC (6), a timing pulse generating unit (7), a cosine/sine signal generating unit (8), first and second digital multipliers (9, 10), first and second digital filters (11, 12), a quadrant discriminating unit (13), an angular velocity computing unit (15), a phase modulation index computing unit (14) and a reference signal generating circuit (1).

18 Digital circuit implementation 4 5 Digital Filter Low pass => DC component kept Digital signal processing apparatus. First to forth heterodyne mixers (2, 3, 4 and 5), an ADC (6), a timing pulse generating unit (7), a cosine/sine signal generating unit (8), first and second digital multipliers (9, 10), first and second digital filters (11, 12), a quadrant discriminating unit (13), an angular velocity computing unit (15), a phase modulation index computing unit (14) and a reference signal generating circuit (1).

19 Digital circuit implementation Digital signal processing apparatus. First to forth heterodyne mixers (2, 3, 4 and 5), an ADC (6), a timing pulse generating unit (7), a cosine/sine signal generating unit (8), first and second digital multipliers (9, 10), first and second digital filters (11, 12), a quadrant discriminating unit (13), an angular velocity computing unit (15), a phase modulation index computing unit (14) and a reference signal generating circuit (1).

20 Digital circuit implementation Digital signal processing apparatus. First to forth heterodyne mixers (2, 3, 4 and 5), an ADC (6), a timing pulse generating unit (7), a cosine/sine signal generating unit (8), first and second digital multipliers (9, 10), first and second digital filters (11, 12), a quadrant discriminating unit (13), an angular velocity computing unit (15), a phase modulation index computing unit (14) and a reference signal generating circuit (1).

21 Digital circuit implementation Digital signal processing apparatus. First to forth heterodyne mixers (2, 3, 4 and 5), an ADC (6), a timing pulse generating unit (7), a cosine/sine signal generating unit (8), first and second digital multipliers (9, 10), first and second digital filters (11, 12), a quadrant discriminating unit (13), an angular velocity computing unit (15), a phase modulation index computing unit (14) and a reference signal generating circuit (1).

22 ,, Quantum Theoretical Performance Limit

23 Sources of nonidealities Nonreciprocity differences in the optical paths of the counter propagating waves Polarization Backscattering Magneto-optical Faraday effect

24 Case Study: RA2100 (KVH Industries)

25 Case Study: RA2100 (KVH Industries) Source: ftp://ftp.uni-duisburg.de/hardware/kvh/ec2k-b.pdf

26

27 Case Study: RA2100 (KVH Industries)

28 Case Study: RA2100 (KVH Industries)

29 Case Study: RA2100 (KVH Industries)

30 Case Study: RA2100 (KVH Industries)

31