US Patent 8970211 Pipe inspection cable counter and overlay management system

An apparatus is disclosed for magnetically sensing and computing and displaying cable distance, and computing and displaying other user-selectable information in a pipe inspection system. At least two permanent magnets are mounted in spaced apart fashion, on either a frame, or a rotatable member supported on the frame for rotation about an axis. A magnetic sensor is mounted on the other one of the rotatable member or frame on which the magnets are not mounted, so that either the magnets rotate around the magnetic sensor or the magnetic sensor rotates between the permanent magnets. The magnetic sensor generates signals representing changes in at least two axes in a composite magnetic field generated by the permanent magnets.