Multipoint Strain Monitoring Technique In Fiber Bragg Grating Sensing System

In order to improve the interrogation technique for a multipoint fiber Bragg grating sensing system,a virtual instrument system based on LabVIEW is introduced.By controlling the transmission time of the analog electrical switch in each channel,the signal pulses come from the FBG sensors were allocated to the corresponding output channels in time-sequence.At the same time,the actions of the switches were synchronized with the wavelength scanning of the F-P filter in ring-cavity fiber laser.With the wavelength chosen technique of ring-laser and interferometric demodulation method of unbalanced Michelson interferometer,a sensor array with 3 FBG elements was addressed successfully.1.An interrogating and demodulating system for multi-node fiber Bragg grating(FBG) strain sensing was developed.The principle of interferometric demodulation technique with unbalanced Michelson interferometer was analyzed,the difference between the two arms should be set in a reasonable length to compromise the demodulation accuracy and the fringe contrast. A determine method of the arm difference was suggested experimentally.2.The research on multi-channel output analog electrical switch controlling was conducted. With the LabVIEW software,the analog electrical switches were programmably operated in sequence,and synchronized with the wavelength scanning of the F-P filter.3.The experiment of the strain monitoring system.An 1×N analog electrical switches were used and controlled to distribute the sensing signals with the digital signal come from DAQ card,thus the synchronization between the motion of the switch and the sawtooth signal scan was realized.The 3 FBG sensor arrays were interrogated successfully.The sensitivity of the sensing system is 1.57°/με,the resolution is 6 nε,and the measurement range is in—672με～672με.