Abstract: There is described a sensor comprising an excitation winding, a signal generator operable to generate an excitation signal and arranged to apply the generated excitation signal to the excitation winding, a sensor winding electromagnetically coupled to the excitation winding and a signal processor operable to process a periodic electric signal generated in the sensor winding when the excitation signal is applied to the excitation winding by the signal generator to determine a value of a sensed parameter. The excitation signal comprises a periodic carrier signal having a first frequency modulated by a periodic modulation signal having a second frequency, the first frequency being greater than the second frequency. In this way, the sensor is well suited to using digital processing techniques both to generate the excitation signal and to process the signal induced in the sensor windings. In an embodiment, the sensor is used to detect the relative position of two members.

Abstract: A detector for reading information stored in a magnetic tag is disclosed, the reader comprising two assemblies of permanent magnets (each containing three magnets) arranged with their magnetic poles in opposition such that the magnetic poles of one triplet are physically opposite the like poles of the other triplet. The magnets are preferably elongate with their long axes being mutually parallel. The two magnet assemblies define between them a gap through which, in use, a tag having magnetic material is passed. Receiver coils are positioned within the gap. The magnet assemblies are preferably rigidly secured within an aluminum housing. Electrostatic screening foils may be placed over the receiver coils.

Abstract: A linear position sensor is provided which employs phase quadrature sensor windings, an excitation winding and a resonator. When an excitation current is applied to the excitation winding, it causes the resonator to resonate which in turn induces signals in the sensor windings. The sensor windings are spatially arranged so that the electromagnetic coupling between them and the resonator varies with the position of the resonator. The excitation windings, phase quadrature windings and resonant circuit are arranged so that the magnetic fields involved in the operation of the position sensor are substantially parallel to each other and the direction of movement of the resonator. Consequently, the effect of rotation of the resonator or lateral movement of it relative to the excitation and phase quadrature windings is alleviated.