Magnetic Imaging of Ferromagnetic Shape with Mobile Hall Sensor Array System M. Norhisam, N. Wei Shin, M. Hamiruce Marhaban and S. Suhaidi Department of Electrical and Electronics Engineering University Putra Malaysia 43400 Selangor, Malaysia Abstract The Mobile Hall Sensor Array system is a dynamic moving device capable of ferromagnetic shape evaluation based on the magnetic flux leakage testing principle. The device consists of a linearly integrated 1-D Hall Sensor array to detect magnetic field changes on a ferromagnetic shape under evaluation. The signal processing application software residing on a computer is developed for the Hall sensor array signals processing which leads to the magnetic image construction of magnetized ferromagnetic shape. This paper presents the principle of operation for Mobile Hall Sensor Array System in the shape detection of ferromagnetic materials. In addition, the signals array processing algorithm implemented in Hall Sensor Signals Array Processing application software is presented. The experimental results illustrated the magnetic image of specimens SS400 mild steel of various shape e.g square, round and triangle. The results proved the ability of Mobile Hall Sensor Array system to perform shape evaluation on ferromagnetic materials. Keywords- Signal Processing, Hall Sensor Array, Magnetic Image I. INTRODUCTION The Magnetic Flux Leakage Testing (MFLT) is proven to be effective for non-destructive testing of ferromagnetic surface such as steel pipeline, oil-gas pipeline, structure of power plants, wire-rope and aircrafts structure [1-8]. The purpose is to evaluate the condition of the surfaces and perform necessary maintenance to avoid fatal accidents. Today, many researchers have proposed the techniques for ferromagnetic surface evaluation in the industries. Most of it is based on the MLFT principle. A.Gasparics et al[1] introduced the fluxset magnetic sensor for magnetic imaging of surface in aviation related non-destructive testing (NDT). J.S.Hwang et al[2] introduced the area-type magnetic camera constructed from 2-D Hall sensor array for ferromagnetic surface cracks evaluation. J.Y.Lee et al[3] proposed the linearly integrated Hall sensor array for ferromagnetic materials evaluation. L.J.Yang et al[4] stated the used of Hall sensor and coil sensor for oil-gas pipeline surface evaluation. X.Li et al[5] used the 3D finite element method (FEM) to calculate and modeled magnetic flux leakage on defects of steel pipeline surface. J.Z.Chen et al[6] proposed the MFLT based evaluation of oil wells surface with Gaussian Kernel RBF Neural Network. Y.N Cao et al[8] used Hall sensor array to capture the 2-D magnetic leakage signals around the surface of a defective wire-rope. This research focused on the design and development of Mo bile H all S ensor Array (MHS) system for ferromagnetic shape evaluation. The ferromagnetic shape magnetic imaging served as the prototype design in developing a MHS system to perform ferromagnetic surface cracks evaluation underneath a non-ferromagnetic surface. The device operation is fully automated during the ferromagnetic shape evaluation without the need of human interaction. It operates based on the MFLT principle where magnetic flux of ferromagnetic shape is sampled and analyzed. The MHS system comprised of three major modules mainly the signals sensing unit (SSU), signals acquisition unit (SAU) and signals processing unit (SPU). The SSU consists of a 1-D linearly integrated Hall sensor array responsible for the detection of magnetic flux on a ferromagnetic shape. The SAU consists of analog multiplexer connected to microcontroller responsible for the digitization of MFLT signals from SSU and digitized signals transfer to SPU. Lastly, the SPU consists of a computer with H all Sensor S ignals A rray P rocessing (H-SAP) application software for signals array processing. II. PRINCIPLE OF OPERATION FOR MOBILE HALL SENSOR ARRAY SYSTEM This section explicitly explains the principle of operation for Mobile Hall Sensor Array (MHS) system. The MHS system detection principle is mainly based on the MFLT principle on the magnetized ferromagnetic shape under evaluation. The magnetic flux from permanent magnet A and B flow across the specimen as the MHS system navigates across in the y-axis direction shown in Figure 1. The 1-D linearly integrated Hall sensor array is employed to detect magnetic field change on the magnetized ferromagnetic shape. Figure 1 below illustrates the cross sectional view of MHS system including the mobile system, permanent magnet bar, 1-D Hall sensor array, analog multiplexer, microcontroller and computer. Figure 1. Cross-sectional view of the MHS system 2011 IEEE International Conference on Signal and Image Processing Applications (ICSIPA2011) 978-1-4577-0242-6/11/$26.00 ©2011 IEEE 1