The Demodulation Method Of Active Homodyne Laser Vibration Measurement System Based On DSP

With the progress of science and technology, laser interferometry technology develops to higher accuracy and greater dynamic range. At the same time, the demodulation technology is demanded higher and higher. In the homodyne demodulation methods, the detection technique of phase generated carrier (PGC) demodulation is one of the high sensitivity detection methods. It has more practical significance and practicability to study digital PGC demodulation method. Therefore, PGC demodulation technique will be very useful in vibration measurement,acceleration measurement and submarine sound signal measurement, etc.In this paper, the main work is to demodulate low-frequency micro-vibration signal. Based on digital signal processing (DSP) technology, laser vibration measurement signal demodulation hardware and software processing platform is established. The content of this paper is focused on the choice of the key parameters, the realization of the PGC algorithm using digital system, and the design and debugging the hardware circuit. The detailed contents are shown as follows:1. The PGC modulation and demodulation theory is discussed systemically. The system parameters are derived from signal demodulation performance indices.2. Signal acquisition circuit, front-end processing circuit and digital demodulation circuit based on TMS320VC5416DSP is designed. The software programme of PGC algorithms is realized.3. The demodulation system noise and its transfer law are researched. Through deriving, the system minimum detected vibration signal is determined.4. The testing platform is constructed and the weak vibration signal produced by nanometer vibration platform is measured. High accuracy measurement of the low-frequency vibration signals ranging from 10-200Hz comes true, the measuring resolution is better than 1nm, and the dynamic range is about 100dB.