Liquid Level Sensor with Two FBGs Embedded in a PDMS Diaphragm: Analysis of the Linearity and Sensitivity.

Eliton Morais,Arnaldo Leal-Junior,Carlos Marques,Maria José Pontes

doi:10.3390/s22031268

Eliton Morais, Arnaldo Leal-Junior + Show 2 more

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https://doi.org/10.3390/s22031268

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Abstract

This paper presents a fiber optic, liquid level sensor system based on a pair of fiber Bragg gratings (FBGs), embedded in a circular silicone (PDMS—polydimethylsiloxane) rubber diaphragm. The measurement principles of this sensor, whose diaphragm structure is about 2.2 mm thick with 45 mm in diameter, are introduced. To analyze the linearity and sensitivity of the sensor, the diaphragm was subjected to compression tests as well as to liquid level loading and unloading. The force and liquid level increase tests showed that inserting two FBGs (0.99453 for force and 0.99163 for liquid level) in the diaphragm resulted in a system with greater linearity than that with individual FBGs. This occurred where FBG1 showed 0.97684 for force and 0.98848 for liquid level and FBG2 presented 0.89461 for force and 0.93408 for liquid level. However, the compression and water level decrease tests showed that the system (R2 = 0.97142) had greater linearity with FBG2 (0.94123) and lower linearity with FBG1 (0.98271). Temperature characterization was also performed, and we found that sensitivity to FBG1 temperature variation was 11.73 pm/°C and for FGB2 it was 10.29 pm/°C. Temperature sensitivity was improved for both FBGs when compared with uncoated FBGs with typical values of 9.75 pm/°C. Therefore, the proposed FBG-based sensor system is capable of simultaneous measurement of force and temperature in a compact diaphragm-embedded system.

Highlights

Fiber optic sensing technology has a huge potential to be used in the industry [1], in health [2], in radioactive environments [3], in explosive environments [4], and in structural health monitoring [5]
With the results of this and previous tests, we found that FBG2 is not as stable as FBG1, this can be solved by replacing FGB2
Based on the sensitivities obtained in the level tests, it was possible to obtain a system withBaasreesdoolunttiohne sceanpsaitciivtyitioefs 3o.b4t0a8inmedminfotrhethleevFeBl Gte1stas,nidt w9.a1s6p8omssmiblfeotrothobetFaBinGa2sfyosrteimnwcrietahsianrgelsioqluuitdiolnevcealpvaacriitaytioofn3, .a4n0d8 3m.4m58fomrmthfeorFBthGe1FaBnGd1 9a.n1d688.m85m3 mfomr tfhoer FthBeGF2BfGor2 ifno-r cdreecarseiansginligquviadrilaetvioenl .variation, and 3.458 mm for the FBG1 and 8.853 mm for the FBG2 for decreasing variation

Summary

Introduction

Fiber optic sensing technology has a huge potential to be used in the industry [1], in health [2], in radioactive environments [3], in explosive environments [4], and in structural health monitoring [5]. In addition to liquid level monitoring, diaphragm-based sensors with built-in FBGs are employed in sensing pressure [25], vibration [26], acceleration [29], and force [30]. Her et al [35] developed a sensor for measuring pressure and water level built from an FBG integrated in an epoxy diaphragm, where the effect of diaphragm thickness on sensor sensitivity and accuracy was investigated. This sensor needed a temperature compensation for practical applications. Based on the sensitivities obtained in the level tests, it was possible to obtain a system withBaasreesdoolunttiohne sceanpsaitciivtyitioefs 3o.b4t0a8inmedminfotrhethleevFeBl Gte1stas,nidt w9.a1s6p8omssmiblfeotrothobetFaBinGa2sfyosrteimnwcrietahsianrgelsioqluuitdiolnevcealpvaacriitaytioofn3, .a4n0d8 3m.4m58fomrmthfeorFBthGe1FaBnGd1 9a.n1d688.m85m3 mfomr tfhoer FthBeGF2BfGor ifno-r cdreecarseiansginligquviadrilaetvioenl .variation, and 3.458 mm for the FBG1 and 8.853 mm for the FBG2 for decreasing variation

Conclusions

Findings