Study On System Of Fiber Chirped Grating Gantry Cable Tension Measurement

Fiber optical grating sensor is a sensor which is made based on Grating wavelength's sensitive to temperature and strain. In addition to traditional electric sensor's function, it also has the advantages of anti-electromagnetic interference, wide measurement range, largely dynamic range, and good stability. They are widely used in composite material and concrete to monitor their structures, and also used in the electric power industry, petroleum controlling, and chemical industry.Fiber Chirped grating, FCG, sensors using reflected light intensity as the modulated signal, have advantages of cost and speed compared to fiber Bragg grating sensors who use wavelength as the modulated signal, and have been used in vibration and stress measurement. To FCG intensity demodulation, fluctuation of output power from light source and power attenuation of the vibrations generated by bending in transmission are major disturbances, particularly in the measurement of an object whose change is slow.According to the characteristics of signal in container crane weighing, a method based on ratio of light intensity is introduced to improve FCG light intensity demodulation, eliminating some main distrubs when FCG is used to measure steady-state signals, and broadening the application of FCG sensing technology.This paper describes FCG ratio method of light intensity and gives a theoretical analysis,and introdues the design of optical route and the way of how to build it.Through the experiment, the result shows when light source power changes in the ratio of 3dB, the output signal changes about 1.5%.To make the ratio demodulation instrument, this designe uses an ARM processor from STMicroelectronics as the core of the device, and this paper introdues the design in full details in both hardware and software in the way of modularization;makes a PC software which can supervises and save the data by LabVIEW. Results of ratio demodulation instrument in gantry cranes cable tension measurement experiment are as follows:when the measure range is 0 to 3 tons, the degree of linear fit was 99.67%, and full scale error of 1.82%, better than the resistance of strain gauge which is indcated about 3%.The main work I have done:1) doing study and research on fiber chirped grating, and making an innovation improve on the optical path of FCG sensing system, according to the characteristics of FCG sensing theory.2) According to characteristics of the measuring signal and measure method on this application, choosing IC wich fit the application well, of these modules and completing the hardware design.3) According to the composition of hardware, completing design of embedded part of software. Build a PC software, so users can easily monitor the status and control and call the data.