Abstract: Displacements of a moving stem are measured by an optoelectronic high precision dimension and displacement measuring sensor. The stem slides in a body on two guides carried by the body. Two adjacent photoreceivers symmetrically positioned on either side of the stem axis are responsive to an optical source. A cover carried by the moving stem is situated between the source and the photoreceivers. The cover includes transparent and opaque parts so the cover movement increases and decreases the areas of the two photoreceivers exposed to the light source. The cover is substantially symmetrical with the contact tip at the stem end relative to the center point between the two guides, whereby mechanical play of the stem in the guides causes the illumination of the photoreceivers to be virtually the same.

Abstract: Apparatus for detecting whether a measured dimension deviates from a nominal value by a predetermined increment. It comprises a feeler for following the surface of a component and a variable area window controlled by said feeler. Two pairs of photoelectric receivers are located behind the window and the photoelectric receivers of each pair receive differential illumination through the window.