METHOD OF DETERMINING VARIATIONS IN THE PREVIOUSLY ADJUSTED NOMINAL DISTANCE BETWEEN THE FACING SURFACES OF A COLOUR SELECTION ELECTRODE AND A DISPLAY WINDOW OF A COLOUR TELEVISION DISPLAY TUBE, AND DEVICE FOR CARRYING OUT THE METHOD

摘要

PHD. 77-078. For a true reproduction in colour television display tubes it is of importance to accurately establish whether the distance between the colour selection electrode and the display window corresponds to the previously adjusted nominal distance. Not only variations may occur in the said distance, but variations may also occur in the nominal glass thickness of the display window. When measured capacitively errors occur in the measured distance as a result of said variations in the glass thickness. These errors are minimized by a method wherein a measuring electrode is positioned on the surface of the display window remote from the colour selection electrode, a screening electrode is positioned on the said surface, which screening electrode surrounds said measuring electrode and has an outer dimension such that sufficient electrical field inhomogenities are produced between the colour selection electrode and the measuring electrode, and the capacitance between the measuring electrode and the colour selection electrode is measured by means of an alternating voltage. In this way variations in the glass thickness up to at most 15% of the nominal thickness produce a negligible change in the measured capacitance. For a range of glass thicknesses of the display window and a range of distances between the colour selection electrode and the display window the outside dimensions of the screening electrode are given. A practical embodiment of a device for carrying out the method is disclosed also.