Abstract: A detection circuit for a position sensor has drive circuitry 3 connected to two impedance elements 1a, 1b having an impedance which varies in dependence on the position of a movable member, so as to provide an oscillating signal dependant on the position of the movable member. A demodulator 4, 5, 6, 8, 13, 14 is provided for synchronously demodulating the oscillating signal to provide an output signal indicative of the position of the movable member. The demodulator includes sampling circuitry 4, 5, 13 for sampling the oscillating signal over two defined sampling periods in each cycle of the oscillating signal and for providing a sample voltage output which varies with variation in the impedance due to a change in the position of the movable member.

Abstract: Optical card reader systems are known in which an optically encoded card is read to provide an output signal. However, in known systems, the card has to be presented in a particular orientation. Described herein is a card (80) which has three code zones (85, 86, 87), the upper zone (85) carries a code in one of its data streams from which a series of clock pulses is derived to assist in the processing of the data in the streams of the zones (85, 87) or (86, 87). Zones (85, 87) carry identical data presented in identical fashion. In order to determine the presentation of the card, start words (83, 84) can be utilised to indicate to the reader which way up and which way round the card is presented.

Abstract: An optical displacement transducer for providing a digital output representative of the displacement of a variable from a datum value comprises a light beam emitter and a light beam receiver disposed on a common optical axis, a digital encoding element comprising an optical grating disposed between the light beam emitter and receiver, the grating extending in a circular path with the grating lines extending substantially radially of the path, means for causing relative rotation between the light beam and the grating about the center of the circular path whereby the light beam as seen by said receiver is in the form of a series of light pulses, a first reference position at a stationary position on the circular path, a second reference position on the circular path and angularly displaced about the center of the circular path from the first reference position whereby a predetermined light pulse count is produced during the relative rotation through the angle between the first and second reference positions, an