Design and Calibration of a Hall Effect System for Measurement of Six-Degree-of-Freedom Motion within a Stacked Column

Abstract

This paper presents the design, development and evaluation of a unique non-contact instrumentation system that can accurately measure the interface displacement between two rigid components in six degrees of freedom. The system was developed to allow measurement of the relative displacements between interfaces within a stacked column of brick-like components, with an accuracy of 0.05 mm and 0.1 degrees. The columns comprised up to 14 components, with each component being a scale model of a graphite brick within an Advanced Gas-cooled Reactor core. A set of 585 of these columns makes up the Multi Layer Array, which was designed to investigate the response of the reactor core to seismic inputs, with excitation levels up to 1 g from 0 to 100 Hz. The nature of the application required a compact and robust design capable of accurately recording fully coupled motion in all six degrees of freedom during dynamic testing. The novel design implemented 12 Hall effect sensors with a calibration procedure based on system identification techniques. The measurement uncertainty was ±0.050 mm for displacement and ±0.052 degrees for rotation, and the system can tolerate loss of data from two sensors with the uncertainly increasing to only 0.061 mm in translation and 0.088 degrees in rotation. The system has been deployed in a research programme that has enabled EDF to present seismic safety cases to the Office for Nuclear Regulation, resulting in life extension approvals for several reactors. The measurement system developed could be readily applied to other situations where the imposed level of stress at the interface causes negligible material strain, and accurate non-contact six-degree-of-freedom interface measurement is required.

Seismic response prediction using intensity measures: Graphite nuclear reactor core model case study

“…Eight interstitial and six lattice columns were instrumented to record the 6-degrees-of-freedom (DoF) motion of the vertically stacked brick columns acquiring measurements at the brick-to-brick interfaces under seismic loading. For this purpose, several interface measurement techniques and systems were developed (Dihoru et al, 2021; Oddbjornsson et al, 2021). An interstitial column comprises 7 filler bricks and 7 interstitial bricks, constituting 13 brick-to-brick interfaces.…”

A mathematical framework for evaluation of column shape profiles for an advanced gas-cooled reactor core model subject to seismic excitation

“…Measurement of the displacement between the interstitial and filler bricks was undertaken using bi-axial Hall Effect sensors, as described by Oddbjornsson et al (2021). A custom calibration procedure, also detailed in Oddbjornsson et al (2021) enabled the 12 individual data channels to be converted to accurate measurements of motion in all six degrees of freedom. Each instrumented interstitial column comprised 13 interface measurements.…”

“…The following discussion describes the data processing techniques after the raw sensor data has been converted to meaningful measurements in SI units. Please refer to Oddbjornsson et al (2021) for a complete discussion of the calibration method.…”

“…However, it is apparent that significant training from a significantly wide source of measurements is required to ensure that a sufficiently robust neural network is developed. For classification of keyed-and unkeyed-interstitial bricks, referred to herein as interstitial and filler bricks respectively, displacement measurements have been calculated using the nonlinear system identification method applied to each brick interface, as described in Oddbjornsson et al (2021). This method allowed direct extraction of six degree-of-freedom (DoF) displacements representing the full translational and rotational movement of an adjacent pair of vertically stacked interstitial and filler bricks.…”

Development of a Low-Cost 6 DOF Brick Tracking System for Use in Advanced Gas-Cooled Reactor Model Tests

“…When the core experiences a seismic event, the presence of cracked bricks increases the dynamic displacement of the core, disrupting the uniform geometry with potential ramifications for fuel cooling and control rod insertion. While instrumentation had been developed to track the relative motion of the uncracked bricks and DCBs [ 4 , 5 , 6 ], the methods used for these bricks were not viable for use with TCBs and QCBs. The particular challenges with measuring the motion between the four QCB components are the potential for relatively large six degree of freedom (DOF) motion between each quarter, very limited space for sensors, and a need for non-contact sensors to avoid the instrumentation interfering with the brick dynamics.…”