Abstract: A detection head unit comprises a stator and a rotor. The stator has four poles disposed circumferentially at an interval of 90.degree.. The poles have primary coils and secondary coils wound thereon. Two radially opposing poles constitute a pole pair. The primary coils wound on the poles constituting the pole pair are connected in series and in opposite phase with each other and one pole pair is excited by a sine wave signal and the other pole pair by a cosine wave signal. The rotor is of such a configuration, e.g. an eccentric rotor, as to change reluctance of the respective stator poles in accordance with a rotation angle and change reluctance in a differential manner between the two poles constituting the pole pair. An output signal resulting by phase shifting the sine wave signal applied to the primary coil in accordance with a rotation angle of the rotor is provided by a secondary coil.

Abstract: About a bobbin, there are wound primary coils in axially displaced locations and wound also is a secondary coil. A core is linearly slidably provided in the bobbin. The primary coils are individually excited by AC signals which are out of phase with each other, e.g. a sine wave signal and a cosine wave signal. The secondary coil thereupon produces an output signal resulting from phase shifting the applied sine or cosine wave signal in accordance with a linear position of the core. Accordingly, the linear position can be detected by measuring phase difference between a reference AC signal and the output signal of the secondary coil. Likewise, velocity and acceleration change may be determined using the position change data.