An Improved Calibration Method to Determine the Strain Coefficient for Optical Fibre Sensing Cables

Pengju An,Kun Fang,Qinglu Deng,Chaoqun Wei,Huiming Tang,Bofan Yu

doi:10.3390/photonics8100429

Abstract

The strain coefficient of an optical fibre sensing cable is a critical parameter for a distributed optical fibre sensing system. The conventional tensile load test method tends to underestimate the strain coefficient of sensing cables due to slippage or strain transfer loss at the fixing points during the calibration procedure. By optimizing the conventional tensile load test setup, the true strain of a sensing cable can be determined by using two sets of displacement measuring equipment. Thus, the strain calculation error induced by slippage or strain transfer loss between a micrometre linear stage and sensing cable can be avoided. The performance of the improved calibration method was verified by using three types of sensing cables with different structures. In comparison to the conventional tensile load test method, the strain coefficients obtained by the improved calibration method for sensing cables A, B, and C increase by 1.52%, 2.06%, and 1.86%, respectively. Additionally, the calibration errors for the improved calibration method are discussed. The test results indicate that the improved calibration method has good practicability and enables inexperienced experimenters or facilities with limited equipment to perform precise strain coefficient calibration for optical fibre sensing cables.

Highlights

The development of a distributed optical fibre sensing system (DOFSS) provides a new opportunity for geotechnical and structural health monitoring [1]
Results and Discussion the mid-section measured by the two laser displacement sensors, εi is the strain calculated by the The tensile load test method, and εwere strain calculated by thethe improved mi is the three sensing cables calibrated both with tensilestrain load test m calibration method
The strain measurement is subject to a measurement repeatability error, which is highly related to the measurement accuracy of the Brillouin optical time domain analysis (BOTDA) interrogator

Summary

Introduction

The development of a distributed optical fibre sensing system (DOFSS) provides a new opportunity for geotechnical and structural health monitoring [1]. By integrating a common optical fibre cable into geologic bodies or a structure, the parameters of interest, such as strain or temperature, along the optical fibre route can be obtained [2]. Brillouin optical time domain analysis (BOTDA) is a widely used technology in civil and geotechnical engineering for strain and temperature measurement due to its high spatial resolution and high measurement accuracy [7,8,9,10,11,12]. To satisfy the engineering requirement, different types of sensing cables have been specially designed and made [13,14,15]

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Methods

Results

Conclusion