Techniques and Materials for Optical Fiber Sensors Sealing in Dynamic Environments with High Pressure and High Temperature

Abstract

We detail a study of the techniques and sealing materials for optical fiber sensors used in dynamic environments with high pressure (>300 bar) and high temperature (>300 °C). The sealing techniques and materials are the key for the robustness of sensors in harsh dynamic environments, such as large combustion engines. The sealing materials and techniques studied in this work are high-temperature epoxies, metallic polymer, metallic solders, glass solder, cement, brazing and electroless nickel plating. Because obtaining high temperature simultaneously with high pressure is very difficult in the same chamber in the laboratory, we developed a new and simple method to test sealed fibers in these conditions in the laboratory. In addition, some sensors using the materials tested in the laboratory were also field tested in real thermoelectric combustion engines. The study also discusses the methods of fabrication and the cost−benefit ratio of each method.

Analysis of Return-to-Zero Error after the First Load of Load Cell

“…The weld cup is a component commonly used for load cell sealing, and its material properties are usually identical to those of the load cell. Especially in the fabrication of steel sensors, weld cup seals have become more common, and it has become a more mature sealing method [35].…”

Metallurgical Aspects of Ni-Coating and High Temperature Treatments for FBG Spectrum Regeneration

“…Compared to surface-bonded sensors, embedded sensors can provide punctual information at certain critical points from inside the structure in real-time [12,13]. In this case, the absence of a coating, or the presence of a polymer coating, reduces the adhesion with the SiO 2 fiber and worsens the performance of the grating, causing an inhomogeneity in the transfer function of the monitored magnitude, whether one wants to insert the sensor directly into a cast matrix (this is the case with low melting metals such as copper), or encapsulate the sensor in a pre-crafted groove, inside material [14].…”