Development of Hall probe magnetic field measurement system using computer vision and rotating stage

Abstract This study presents a measurement system for Hall probe accelerator magnets that incorporates a triple camera array for alignment and a rotating stage to capture magnetic-field harmonics. The camera array functions similarly to a total station, combining features of a theodolite and range finder. A color marker was used as a trace-mark target to position the Hall probe at the mechanical center of the magnet. Techniques such as color-based object tracking, stereo vision, Canny edge detection, and Hough-transform algorithms were implemented to achieve this. In conventional Cartesian coordinates, we measured the radial-direction magnetic fields, denoted as Br , by calculating Bx , and By . However, with the use of a rotating stage that allowed the rotation of the Hall probe, we measured the Br directly in cylindrical coordinates. Subsequently, we compared the harmonics of both methods. Three identical 1T/m reference quadrupoles were measured. The experimental results confirmed that the alignment of the magnet and Hall probe achieved repeatability ranging within an approximate value of 200 μm. The proposed camera array system will be installed at Korea University's in-house Single Stretch Wire magnet measurement system to assist magnet and wire alignments.