Design of a GMR sensor array system for robotic pipe inspection

In this paper, the design and implementation of a GMR sensor array for utility pipe inspection is presented. Four GMR sensors with sensitivity of 0.9-1.3 mV/V are mounted uniformly around the circumference of a ring housing. Two bar magnets, located 180° apart, are also mounted in the housing to magnetize the pipe for accurate defect detection. The instrumentation circuit, including 3 buffers, a difference amplifier, and a 4^th-order low-pass filter, generates a clear smooth defect signal.