GB626161A - Improved arrangements for eliminating parallax in indicating instruments - Google Patents

Abstract

626,161. Cathode-ray oscillographs. STANDARD TELEPHONES & CABLES, Ltd., and CLEAVER, R. F. March 24, 1947, No. 7991. [Class 37] [Also in Group XIX] A cursor line, spaced above an indicating face and below a colour filter, is illuminated by light to which the filter is opaque except along a narrow band parallel to the cursor line, while the filter is transparent to light illuminating or comprising the indication on the face. A cursor line 2, engraved on a transparent plate 1, spaced between a cathoderay tube 7 and colour filter 3, protected by a cover glass 4, is illuminated by lamps 9 emitting light, say red light, to which the filter 3 is almost opaque except along a thin slot 5 parallel to the line 2, while the filter 3 is transparent to light from the cathode-ray tube trace, say green light, and to light from lamps 10, say blue light, which illuminates an annular scale 8. Thus the trace and scale can be viewed from above at any angle while the cursor can only be seen distinctly when viewed normally. The colour filter may comprise a dyed gelatine sheet or a similar coating on the undersurface of the cover glass 4 or a coloured plastic sheet. Precautions are taken to avoid edge glow from the slot 5. In a second embodiment the source of light for the cursor may be placed behind the fluorescent screen and the cursor may comprise parallel slots in two spaced colour filters. The transparent plate 1 may then be eliminated.