Abstract: The rotation position of a rotor (2) rotatable around a rotation axis (1) is determined by mounting a magnetic source (2.1) on the rotor, by providing on a stator (3) at least three sensors (4, 5, 6, 7) for measuring the magnetic field of the magnetic source and being arranged in at least two pairs (4/5, 6/7), calculating the difference of quantities measured by the two sensors of each sensor pair, calculating the ratio of the difference values of two pairs and comparing the ratio with a predetermined function of said ratio versus the rotation position. This rotation position determination is very robust against offset and sensitivity variations common to all sensors (4, 5, 6, 7) and against external magnetic fields and can easily be made robust against mechanical tolerances between rotating and stationary parts also. In a preferred embodiment, there are four sensors (4, 5, 6, 7) arranged at the corners of a square perpendicular to and symmetrical relative to the rotation axis (1).

Abstract: The method serves for dynamically compensating the offset voltage of a Hall device. The Hall device can have either a platelike structure with at least two contact pairs, or any other arrangement deriveable by conformal mapping. The contact pairs are angled by e.g. 90.degree.. Each pair is supplied with a periodically alternating current whereby the phase shift of the supply currents corresponds to the spatial phase shift of the contact pairs and is e.g. 90.degree.. Superposition of the supplied currents results in a continuously spinning current vector in the Hall device. By measuring simultaneously the voltages between corresponding terminals, a signal consisting of the Hall voltage and a periodic offset voltage can be isolated. The offset voltage is eliminated by averaging the signal over at least one period.