FG-compass is a general movement measurement device, which is able to measure motion information (including the heading, pitching, roll, heave, surge, sway and rate of the carrier, etc.) and true north. This device includes a fiber-optical gyroscope (FOG) inertial measurement unit (IMU), display and control device and a power supply device.
Since the FOG is used in the compass, it requires neither maintenance nor recalibration; its strapdown IMU structure enables straightforward, effective use with which no traditional mechanical gyrocompass can complete; since it is small in size and light in weight, it is easy to carry and install.
The compass enables to find the true north and to be powered up in three modes, which are dock start-up mode, maritime autonomous start-up mode and maritime integrated start-up mode.
Dock start-up mode: It requires the vehicle is static or quasi-static, such as the ship is at anchor or the vehicle is in idle. After the starting time which lasts 30 minutes, the compass switches to navigation mode.
Maritime autonomous start-up mode: It requires the vehicle is of uniform motion state in the first 10 minutes. After the starting time which lasts 60 minutes, the compass switches to navigation mode. It also requires the velocity information from the log in the starting process.
Maritime integrated start-up mode: It requires the vehicle is of uniform motion state in the first 5 minutes. After the starting time which lasts 60 minutes, the compass switches to navigation mode. It also requires the location information from GPS or Beidou in the starting process.
2 Technical description
The core of FG-compass is the FOG-IMU. The IMU contains three FOGs in 0.01 deg/h class, three accelerometers in 0.1mg class and DSP computation unit. Figure 1 shows its internal structure. Its dimensions and physical characteristics are given in Appendix A.
30 min (Dock start-up mode)
60 min(Maritime autonomous start-up mode)
60 min(Maritime integrated start-up mode)
Roll & Pitch
< 0.05 deg
< 0.15 deg, Secant latitude
< 0.10 deg