A novel signal processing algorithm for FFPI and its sensor system application

Abstract

A novel digital signal processing algorithm using a pulse-modulated, fiber-optic Fabry-Perot sensor system with temperature as the measurand is devised and implemented. Measurement of change in temperature makes use of the frequency chirping of a repetitively pulsed laser to maintain high sensitivity and enable the direction of temperature change to be determined unambiguously. The algorithm can also be directly applied to monitoring of other measurands using appropriate adapters and calibration procedures. Using the same system configuration, a simple modification of the processing algorithm makes it possible to develop an absolute parameter monitoring system. An approximate starting value can be used instead of an exact one, giving the system more degrees of freedom. Automatic detection of the starting value of the parameter used as a reference point at the beginning of the measurement opens the door to a practical sensor system. Adding one more sensor to the same system setup provides a simultaneous measurement of temperature and strain. This is done by configuring one sensor to experience only temperature change and the other to experience both temperature and strain changes. The measured strain will be calculated by finding the difference between the two measured values of round-trip phase shift in the interferometers. Depending on the need, appropriate modification of the algorithm can be used for simultaneous measurement of temperature and other parameters of interest.