Long Period Testing and Validation of the Fully Analog Interrogation System for FBG Sensors

The proposed manuscript investigates the application of Fiber Bragg Grating (FBG) sensors in safety scenario, by means of a full analog interrogation system. From the optical point of view, among the passive devices composing the system, the main component is the Arrayed Waveguide Grating (AWG), whose working principle is to filter the single FBG spectrum into a dedicated channel. The AWG output is connected to a full analog electronic board working as a conditioning circuit to set the output in terms of electrical current, in the range 4-20mA. Along these lines, the proposed interrogator is fully compatible with PLC systems, compliant with safety scenarios. In this study, the system functionality is validated in a real-case scenario, by installing it at Compact Muon Solenoid (CMS) experiment at CERN (Geneve, CH), in the Underground Surface Cavern (USC). Two FBG sensors are employed monitoring the temperature of two pumps for 8 months of continuous acquisition. The system has been previously calibrated, correlating the output current with the temperature value, obtaining a resolution below the Celsius degree.