Apparatus for contact-less measuring the value of a difference angle between two parts rotating about a common axis

An apparatus for contact-less measuring the value of a difference angle between two parts rotating about a common axis, the apparatus comprising:

• a stator attached to one of the two parts, the stator having a permanent magnetization forming of a number of at least two magnetic pole pairs, each pole pair consisting of two magnetic poles of opposite signs, and the signs of the magnetic poles of all pole pairs alternating in the direction of rotation about the common axis;
• a ferromagnetic rotor attached to the other of the two parts, the rotor having a number of at least two pole ends for magnetically scanning the stator, the poles being successive in the direction of rotation about the common axis, and the number of the pole ends being the same as the number of the pole pairs of the stator;
• a first air gap between the pole pairs of the stator and the pole ends of the rotor, each pole end of the rotor facing one pole pair of the stator over the first air gap, all conditions of arrangement of all pole ends and the corresponding pole pairs being the same;
• an accessible and rotationally symmetric second air gap of continuous dimensions between the stator and the rotor, a magnetic flux across the second air gap being changed according to the difference angle between the rotor and the stator;
• and
• at least one magnetically sensitive element for determining the magnetic flux across the second air gap, the magnetically sensitive element being arranged at a fixed position in the second air gap and not being rotating with one of the two parts about the common axis.