High Speed Signal Acquisition And Processing For Mechanical Dithered Ring Laser Gyro

Ring laser gyro (RLG) which is based on the Sagnac effect is used in many fields such as inertial navigation as a rotation sensor. The mechanical dithered ring laser gyro (DRLG) is the most widely used one in all kinds of RLG. Two beat frequency signals withπ/2 phase difference are generated in DRLG by signal readout apparatus. Information includes lock-in threshold, dither modulation, discharge noise and so on can be obtained by acquisition and analysis of DRLG signals. Rotation rate also can be obtained by signal processing which includes phase demodulation, signals counting and getting rid of dither signals. In the dissertation, a system which is used to acquire and process DRLG signals is designed. Lock-in threshold is obtained by acquisition and analysis of DRLG signals. High resolution signal processing is realized by studying processing method of DRLG signals and designing of signal processing system.In the first, hardware of DRLG signal acquisition and processing system is designed. Analog-to-digital converter (ADC) is used to acquire DRLG signals and FPGA is used to process signals. Circuit board communicates with computer by way of USB and RS-232. SARAM is used as a cache and proves enough address space.In the second, the design of DRLG signal acquisition system is introduced. The system has two 14 bits 60MSPS acquisition channels, can acquire two DRLG beat frequency signals with high speed and high accuracy. A PC program is used in this system to control the working parameters of data acquisition such as sampling mode and sampling period. The FPGA in the board receives commands from the PC and control the ADC, SDRAM and USB interface to accomplish the acquisition task. SDRAM is used for data caching. The USB interface microcontroller which works in SlaveFIFO mode communicates with the computer.In the third, high resolution signal processing of DRLG is realized. Analog beat frequency signals of DRLG are converted into digital signals and then subdivided into 16 beat frequency signals withπ/16 phase difference alternately. Square signals are obtained by zero crossing detection. Counting pulses is obtained by designing phase demodulation logic of fourfold frequency, eightfold frequency, sixteen fold frequency and thirty-two fold frequency. FIR filtering and dither stripping are used to get rid of dither signal from the counting signals and obtaining the rotation rate of DRLG.At last, the signal acquisition and processing system designed in the paper is used to carry out some experiments with DRLG. Amplitude relationship between harmonics of DRLG is analyzed based on the equation of motion for the phase difference between the clockwise and counterclockwise running waves. Lock-in threshold is obtained by analysis the signals sampled from DRLG which rotates at the same speed without dither. A lot of tests are carried out on signals generator and DRLG. Test results prove that signal processing system works stably and resolution of DRLG is improved by increasing frequencies of phase demodulation. Allan variance analysis prove that quantization error is the main error source when getting ride of dither signal with the method of dither-stripping, and that high resolution signals processing effectively reduces quantity error and improves the accuracy of DRLG.