Research On The Demodulation Technology Of Distributed Optical Fiber Sensor System

AbstractDistributed optical fiber sensing technology plays a significant role in distributed multi-point temperature and pressure measurement for its characteristics of removing the requirement for a lower environment disturb in traditional sensors and avoiding the construction inconvenience for multi-point installation of traditional sensors. To satisfy the needs of engineering applications, distributed optical fiber sensing technology has received increasingly interests in the specific areas of measurement with a development following the direction of high-precision, low-cost, high reliability, and real times.The simultaneously demodulation technology of the temperature and strain as well as the data acquisition of fiber temperature sensor and its signal processing system design are studied for the sensing detection system in this article. Firstly, a microwave electro-optical modulation based spontaneous Brillouin scattering heterodyne detection system is proposed and analyzed by comparing the demodulation schemes of temperature and strain when they coexist at the same time. Secondly, this dissertation design the embedded software components in the data acquisition board and signal processing board of a distributed optical fiber temperature sensor based on the primary device with TMS320VC5416 type digital signal processing (DSP) chip. The software mainly includes board control of preparing reception, signal processing subroutine, serial communication subroutine, accomplish of signal reception, noise reduction, demodulation and personal computer (PC) ccmmunication. Finally, the embedded software is developed to co-exploit the data acquisition board and signal processing board, by extensively testing the signal and analyzing the data of the sensor, a group of best parameters have been obtained by regulating the theoretical modulation coefficient according to the experiment data, and the reation of the noise reduction and demodulation precision is discussed in detail.The results firstly show that in the spontaneous Brillouin scattering heterodyne detection system based on microwave electro-optic modulation, when the temperature and strain impact on the sensing fiber at the same time, the fitted demodulation coefficient is highly accordance with the reported experiment results. The demodulation precisions of temperature and strain are 1℃and 100με, respectively. Secondly, the reception preparing subroutine, data receiving subroutine, data noise reduction subroutine, temperature demodulation subroutine and PC serial communication subroutine are debugged in the control board correctly in view of CCS 3.3 software design, respectively. Thirdly, by combining the embedded software and hardware, DSP can control the system to work in a continue receiving status. Then, the Raman effect based distributed temperature sending signal is received, processed noise reduction, demodulated and displayed in the screen. The best demodulation precision of the system is 3℃.