China
Africa
Explore chapters and articles related to this topic
Sensor Applications
Published in Luc B. Jeunhomme, Single-Mode Fiber Optics, 2019
The concept of reciprocal configuration has been widely accepted, improvements are still needed to get the best possible performances. In particular, it is very important to use a broadband source. As a matter of fact, the FOG can be analyzed as an interferometer with two primary waves which are perfectly in phase at rest because of reciprocity, but there are also a lot of secondary parasitic waves generated by back-reflection, backscattering, and crossed-polarization coupling. If the source is coherent, the two primary waves serve as a local oscillator for an efficient coherent detection of these various low-power parasitic waves. The use of a broadband source avoids this problem because the path difference between the primary waves and the parasitic waves is much longer than the coherence length of the source, which eliminates these spurious interferences. Notice that this does not limit the dynamic range of the system because practical FOGs are working only on the first fringes of the Sagnac interferometer. This was demonstrated as a very good solution [37] to reduce the noise induced by coherent Rayleigh backscattering [38]. In particular, superluminescent diodes (SLDs) [32] are commonly used as the optimal source of FOGs, because of their broad spectrum and their high coupling efficiency into a singlemode fiber. This applies also to back-reflections at the various interfaces, that cannot be completely eliminated, even when using tilted interfaces [39].
Optical fiber sensors
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
John P. Dakin, Kazuo Hotate, Robert A. Lieberman, Michael A. Marcus
A FOG detects rotation relative to an inertial frame. The basic operating principle of this sensor is based on a concept known as the “Sagnac effect” [54], which originally used two optical beams, each directed in opposite directions around loops using mirrors, before being caused to interfere on a detector. The basic configuration of the all-fiber version is shown in Figure 11.18.
Mass data methods
Published in W. Schofield, M. Breach, Engineering Surveying, 2007
Fibre optic gyroscopes (FOG) use the same principle but instead of using a simple square or triangular path, the light is carried in a fibre optic coil of many turns. The main problem with this approach is strain distribution in the optical fibre caused by temperature changes and accelerations of the platform. See Figure 14.53.
Pavement surface defect recognition method based on vehicle system vibration data and feedforward neural network
Published in International Journal of Pavement Engineering, 2023
Jian Liu, Yusen Wang, Hongzheng Luo, Gaohang Lv, Feng Guo, Quanyi Xie
The test equipment used in this study is illustrated in Figure 1. The test equipment is integrated with a vehicle, industrial camera, POS-GX7100 INS, and an industrial personal computer (IPC) and equipped with a light supplement device. The POS-GX7100 INS is a system that can directly provide geo-referential position and attitude information for a mobile remote-sensing unit. The system consists of an inertial measurement unit (IMU), position and orientation computer system (PCS), and antenna. A high-precision fibre-optic gyroscope and quartz flexible accelerometer are used inside the IMU. The PCS can store inertial navigation and GPS raw data, and it integrates a TRIMBLE BD 970 three-system receiver. The optimal attitude accuracy of the original data collected by the INS is 0.015°, the speed accuracy is as much as 0.2 m/s, and the original data output is 200 Hz. The onboard industrial camera takes 26 pictures per second.
Performance evaluation of low-cost GPS/INS in-motion alignment model under ECEF frame
Published in International Journal of Image and Data Fusion, 2020
Yunrui Zhang, Qiuzhao Zhang, Chun Ma
This section presents the experiments’ results to verify the INS initial alignment attitude errors algorithm (model 1–3) in -frame developed in this paper. To simulate the low-cost INS in-motion alignment test, we gathered a group of vehicle GPS/INS navigation data. The test employed two sets of GPS receivers and one low-cost IMU (SPAN-CPT). One of the GPS receivers was set up as static reference, and the other one was placed on the top of the test vehicle together with the IMU. The data were logged for post processing. The SPAN-CPT IMU consists of three-axis open-loop fibre optic gyroscope and three-axis MEMS accelerometers. Table 1 shows the SPAN-CPT’s technical data for reference. The sampling frequencies of the GPS and IMU are 1 Hz and 100 Hz, respectively. Figure 2 shows the ground track of the test vehicle, and Figure 3 shows the geodetic heights of the test area.
Autonomous underwater vehicles - challenging developments and technological maturity towards strategic swarm robotics systems
Published in Marine Georesources & Geotechnology, 2019
N. Vedachalam, R. Ramesh, V. Bala Naga Jyothi, V. Doss Prakash, G. A. Ramadass
Precision gyroscopes for measuring the vehicle attitude changes in the angular DOF include the ring laser gyroscopes (RLG) and the interferometeric fibre optic gyroscope (I-FOG). Their technologies are in a highly advanced stage with extremely low bias stability, low angular random walk and capable of determining the true north using the true north seeking algorithms (Lefevre 2014a; Zhang and Liu 2017).These gyroscopes are immune to earth’s magnetic field and hence capable of providing effective measurements in the Polar Regions where magnetic field lines are near-vertical impairing use of traditional magnetic compasses (Lefevre 2014b). The RLG has attained full technological maturity with the ultimate challenge of “lock-in effect” experienced at very low rotation rates being overcome by the mechanical dithering technique. But RLG needs a larger volume to increase the length of the optical cavity, which makes it expensive and bulky (Lefevre 2013). The I-FOG characterized by their smaller footprint, light weight, wide dynamic range and faster response have attracted significant interest. The residual limit of the I-FOG bias stability is due to the ambient temperature time-transient, which when controlled could result in a long term bias stability of about 10−5°/h and capable of meeting the strategic grade requirements for underwater navigation (Ramadass et al. 2017). The advancements in the navigation grade accelerometer technologies and vehicle velocity measurements based on Doppler velocity has given a significant confidence to realize precise Doppler velocity-aided NS (Ellingsen 2008).