1350702 Movement sensor SOC D'OPTIQUE PRECISION ELECTRONIQUE ET MECANIQUE 19 April 1971 [20 March 1970] 24902/71 Heading G4H A system for generating electric signals representing relative movement between two members includes a sensor fixed to one of the members and including at least two detectors responsive to energy received from a graduated track fixed to the other member, the track consisting of a regular alternating series of marks and spaces, and a reshaping device comprising a comparator in which the undulating signal produced by one of the detectors on relative movement between the two members is compared with a reference signal derived from the signal produced by at least one other of the detectors to produce a rectangular signal. Various embodiments are described using various numbers of detectors and comparators the signals from the detectors being variously permutated in pairs for comparison. The detector system may employ a light source together with photoelectric detectors and a graduated track of alternate transmissive and opaque sections or may be magnetic. In the embodiment illustrated in Fig. 6 five detectors 401-405 are provided. The detectors are spaced by a distance 2D/n where D is the length of a mark or space and n is the number of detectors. The signals from the detectors are passed via impedance matching circuits 11-15 to comparators 21-25 and 61-64, the latter comparing signals from the detectors with intermediate signals derived from two other detectors while the former compare signals from one detector with those from another. The parallel outputs of the comparators are a coded representation of the relative positions of the two members. The outputs drive a number of multi-cathode digit tubes via a logic circuit. The slopes of the edges of the pulses may be varied using a slideable mask 3.
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