Wireless coupling for LVDT sensor for reactor applications

Abstract

Wireless coupling can offer significant advantages for in-reactor applications. For instance, wireless signal couplings can avoid electrical feedthroughs penetrating fuel cladding or other high-temperature pressure barriers in fuel performance testing. This paper presents a feasibility study of a wireless coupling technology for the linear variable differential transducer (LVDT), as LVDTs have been successfully demonstrated in reactor applications and can be used to measure a variety of physical parameters. The coupling technology utilizes mutual inductance at a low frequency to transfer power into and signal out of a stainless steel pressure barrier. Using Kirchhoff’s law and magnetic circuit analysis, a theoretical model is developed, including the LVDT, wireless power coupling parts, and wireless signal coupling parts. The LVDT is assumed to have a constant inductance of the primary coil and the sum of two secondary coils. An experimental system is built to test and verify the performance of the technology with a commercial LVDT. The experimental setup has an input voltage limitation to prevent the excessive heating. The non-linearity of the commercial LVDT is ±0.77% as measured in the lab. After coupling the LVDT with the wireless system, the measurement non-linearity is increased to ±1.26%, which shows the wireless power and signal transfer can be applied with LVDTs with limited additional measurement uncertainty. The theoretical model prediction agrees with the experiment results, with the maximum discrepancy of 1.5% between prediction and experiment. The model and experimental results of this study can be directly used to guide the design and optimization of wireless LVDT measurement systems for future in-reactor experiments.