Plastic optic fiber sensor for cumulative measurements

Sensors are typically designed to produce outputs related to the instantaneous value of the quantity of interest; however situations exist where an output related to the total, cumulative or ´integral´ exposure to the quantity of interest is required. This paper describes a low-cost optical sensor for the monitoring of the total exposure to sulphide vapors exploiting a non-reversible chemical reaction and the evanescent field absorption in plastic optical fibers. The sensor is particularly suited for extensive use in cultural heritage conservation monitoring, being intrinsically safe and also quite cheap since the interrogation does not require coherent light sources and spectral analysis. Some prototypes of the proposed sensing system have been produced and tested in laboratory, obtaining a good sensitivity and a fast response.