Study on Performance of FBG Hygrometer Based on Polyimide Coating Technology

Abstract:

In order to study the performance characteristics of polyimide-coated Fiber Bragg Grating (FBG) hygrometer, the saturated salt solution was used to control the ambient humidity, and the variation of FBG center wavelength with relative humidity was tested. The effect of temperature on the sensitivity coefficient of humidity was studied, and the simultaneous measurement of temperature and humidity by this hygrometer was achieved. The results showed that: (1) Within the humidity range of 34.7% to 93.1% in the experimental design, the polyimide-coated FBG humidity meter had a good response to humidity changes. During the humidification and dehumidification processes, the center wavelength exhibited a clear linear relationship with relative humidity, and the humidity sensitivity coefficient ranged from 5.1 to 15.7 pm/%. (2) The thicker the polyimide coating, the higher the humidity sensitivity, and the linear correlation degree between the center wavelength and relative humidity was also higher. (3) Taking the humidity meters No.2 and No.4 as examples, the relative errors of the humidity sensitivity coefficients of the two humidity meters due to a 20 ℃ temperature change were 4.82% and 3.11% respectively. The influence of temperature on the humidity sensitivity coefficient was very small, and its effect on the humidity sensitivity coefficient can be ignored when the temperature change was not significant in actual measurement. (4) Taking the humidity meters No.2 and No.4 as examples, the tempe-rature sensitivity coefficient and humidity sensitivity coefficient were obtained through indoor experiments, and a mathematical matrix for simultaneously measuring temperature and humidity was established, enabling the FBG humidity meter to achieve simultaneous measurement of environmental temperature and humidity.