Encircling eddy-current transducers with rotating magnetic field have many applications with regard to the testing of cylindrical products. Indeed, contrarily to standard encircling differential transducers, they are sensitive to any kind of flaws, including long ones, and can determine their angular positions. In addition, the rotation speed of the magnetic field can easily reach values much larger than those possible with rotating probes devices. As a consequence, they make possible the inspection of the whole surface of products moving at very high speed (up to 80 meters per second for hot wire being rolled). Finally, the mechanical simplicity of these transducers enables the insertion of cooling circuits and, therefore, the testing of hot products.