Abstract: A photoelectric position indicator comprises a scale phase grating, and a scanning unit movable along a measuring direction and comprising a scanning phase grating, which is movable relative to the scale phase grating, a light source, a collimator, and photodetectors, which from the interference patterns formed by the light diffracted by the gratings receive groups having a predetermined order of diffraction and produce periodic phase-displaced actual-value signals in dependence on the orders of diffraction of said groups during a movement of the scanning unit relative to the scale phase grating. To ensure a generation of signals which can easily be evaluated and to permit larger assembling tolerances, the scanning unit comprises a light-directing phase grating arranged to fan the light from the light source transverse to the measuring direction so as to form component light beams, and the photodetectors receive the groups of the interference patterns generated by one of the component light beams.

Abstract: An incremental length measuring system comprises a scale member, which is provided with a measuring scale, a scanning unit having scanning elements for scanning the scale and for generating measured-value signals in response to the scanning of the scale, and an analyzing unit for analyzing the measured-value signals. The scale member comprises a reference track, which is parallel to the measuring scale and provided with a plurality of selectable reference marks associated with respective reference points. The scanning unit comprises a plurality of scanning elements associated with respective ones of the reference marks. A selector switch is provided, which is movable in unison with the scanning unit and is operable by permanent magnet devices, which are associated with any of the reference marks when it has been selected and are contained in a protective housing that contains the scale member and the scanning unit.