The authors have studied a system, consisting of superconducting and ferromagnetic cylinders, and a magnetic field sensor for selectively detecting a magnetic dipole parallel to the extension of the axis of the cylinders. The superconducting cylinder has an open slit in its side so that the magnetic field from the dipole can be measured selectively according to its diamagnetic characteristics. The magnetic fields detected by the sensor are estimated with the aid of magnetic field analysis. It may be possible to use the system for positioning of one or two parallel dipoles. The system will be useful for nondestructive testing of metallic materials. ©1997 American Institute of Physics.