Signal Processing Circuit Of Interferometric Fiber Optic Gyroscope Design And Implementation

Fiber optic gyroscope (FOG) is one kind of fiber optic sensors based on Sagnac effect, which is used to measure inertial angular rotation. FOG can also be divided into Interferometric FOG (IFOG), Resonator FOG (RFOG) and Brillouin FOG (BFOG) because of their different principles. Researchers had study IFOG deeply and used them widely in industries, while RFOG and BFOG are still in phase of experimental research. According to different signal processing schemes, there are two kinds of IFOG:open-loop IFOG and closed-loop IFOG.Here, I propose and realize a new open-loop solution using linear variable differential transformer chip (LVDT). In this solution, I use LVDT to generate a sine signal as modulation signal, whose frequency is 30 KHz. The output contains both fundamental harmonic and second harmonic, which has information about sine and cosine values of Sagnac phase respectively. So I use two bandpass filters to separate them from other harmonic signals. For the second harmonic, it can be demodulated by LVDT directly, and fundamental harmonic should be demodulated by a signal which has phase shift from modulation signal. Finally, we can get tangent value of Sagnac phase. When IFOG is used with low angular rate, the result is nearly linear. The test result shows that its scale factor is 0.2769V/°/s, its zero basis is-49.6°/h, and the standard deviation of its output is 6.6489°/h.In the all digital close-loop solution, I use square wave signal as modulation signal and step wave signal for feedback signal. Before I can confirm period of the square wave (which is twice as much asτ), I need to test transit time through the sense coil-τ. By sampling the output of IFOG with a high speed rate, I subtract one signal from its adjacent ones, and consider it as error signal. Error signal is used to generate a step wave signal by integral feedback control, which can compensate for Sagnac phase. Square wave signal and step wave signal are put together on phase modulator (LiNbO3). In addition, in order to eliminate temperature’s influence on circuit and LiNbO3, I introduce the second loop into system. With the second loop, I can adjust the gain of feedback channel to keep 2n reset voltage accurate. The final results can be sent to computer by UART which is based on FPGA. As a result, this FOG’s nonlinearity of scale factor is 163ppm, its zero basis-4.552°/h, its basis stability is 0.03°/h, and with its random walk coefficient is 0.00892°/h。...