Design Of Signal Demodulation And Automatic Calibration System For Fiber Bragg Grating Temperature Sensor

Fiber Bragg grating sensors have made a quick access to a wide range of applications due to its unique advantages since its emergence. Especially in the power system, the Fiber grating temperature sensor has played a significant role in the on-line temperature monitoring system because of its good to meet the requirements of the development of power system automation and has anti-electromagnetic interference, suitable for long-distance transmission. But the current existing production and calibration level of the fiber grating temperature sensor largely limits its large-scale applications; at the same time, the lack of uniform standards in sensor production and its inefficient calibration become an important factor restricting its development.Fiber Bragg grating sensor detects its refection wavelength change to report the change of the measured physical quantity, which is actually a wavelength coding. So if we want to ensure the measurements accuracy of fiber Bragg grating sensor, we must achieve high-precision detection on fiber Bragg grating wavelength change. Wavelength demodulation is to measure the special signal of the fiber Bragg grating wavelength modulated by the measured physical quantity and to detect the tiny changes of reflection wavelength. Since then, the wavelength demodulation needs a high enough resolution, and requires a lightweight, reliable and easy to operate features in real applications.The thesis is mainly to discuss the signal demodulation of fiber Bragg grating temperature sensor and design an automatic system on this basis, which can improve the automation level of the fiber Bragg grating temperature sensor calibration. The system is designed to realize the bath temperature automatic control and automatic generation of the calibration formula. It uses advanced automation technology instead of mechanical cumbersome manual, which can save labor resources and solve the inaccurate problem of manual calibration. And also the system can greatly shorten the production cycle of the sensor system, reduce the production cost and make the sensor calibration efficient, stable and accurate. All of these lead to meet the growing application requirements of fiber Bragg grating temperature sensor.Fiber Bragg grating temperature sensor auto-calibration system includes high-precision thermostat bath, signal demodulation system, host computer and system software. Some specific works of the subject are signal demodulation system design, control circuit design and system software design. Signal demodulation system consists of optical switch module and demodulator module, respectively, to achieve the channel expansion and wavelength demodulation of the sensor. High-precision thermostatic bath provides a stable calibration constant temperature field. The data communication between demodulation system, thermostatic bath and host computer is done by the system software, which can also complete the wavelength data storage and wavelength data processing work.In learning the temperature sensing properties of fiber grating we can know that the fiber Bragg grating sensor has a good linear relationship between the temperature and wavelength. Sensor calibration work is to find the best coefficient and constant to ensure the sensor accuracy through a certain algorithm. In the subject, the least squares method for curve fitting is used to get the equation. In practical engineering use we can measure the reflection wavelength to calculate the corresponding temperature value.After all the work has done, auto-calibration system needs an experimental analysis to verify the results of calibration. The calibration results in the laboratory show that the sensor accuracy meets the engineering requirements well; calibration results are accurate and reliable. The auto-calibration system can be large-scale use in practical engineering applications.