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AssigneeU.S. Philips Corporation
InventorsJacob van den Berg, Rolf Schmidt
Estimating the term…
The invention relates to a method of determining variations in the previously adjusted nominal distance between the facing surfaces of a color selection electrode and a display window of a color television display tube in places situated near the corners of the display window. In this method the capacitance variations in that distance are determined by measuring a capacitor one electrode of which is formed by the color selection electrode and the other electrode is formed by a measuring electrode surrounded by a screening electrode, the measuring electrode being provided on the outer surface of the display window. By eccentrically moving the measuring electrode in a direction towards the corner of the display window relative to the screening electrode and by a suitable choice of the outside dimensions of the screening electrode, capacitance variations as a result of glass thickness variations in the display window are made negligibly small with respect to the capacitance variations due to variations in the previously adjusted nominal distance between the facing surfaces of the color selection electrode and the display window.
A capacitive method of measuring variations in a previously adjusted nominal distance between facing surfaces of a color selection electrode and a substantially rectangular, planar portion of a display window of a color television display tube, said planar portion being made of glass of a nominal thickness and the display window having an edge portion extending in a direction normal to the plane of the planar portion, said method comprising the steps of positioning, near one corner of the planar portion on the surface thereof remote from the color selection electrode, a metal measuring electrode and a metal screening electrode disposed about and surrounding said measuring electrode, said measuring and screening electrodes being arranged such that the center of said measuring electrode is spaced from the center of said screening electrode along a diagonal line extending from said one corner to the opposite corner of the planar portion, to thereby form a capacitor defined by said color selection electrode and said measuring electrode, said screening electrode having outside dimensions such that variations in the thickness of the planar portion from said nominal glass thickness of at most 15% result in variations in the capacitance of said capacitor which are negligible with respect to variations in the capacitance of said capacitor resulting from variations in the distance between the facing surfaces of said color selection electrode and the planar portion of the window from said nominal distance, and measuring the capacitance of the capacitor formed by said color selection electrode and said measuring electrode.
An apparatus for capacitively measuring the distance between the facing surfaces of a color selection electrode and a substantially rectangular glass display window of a display tube, said apparatus comprising a planar, metal measuring electrode, a planar, metal screening electrode disposed about and surrounding said measuring electrode such that the center of said screening electrode is spaced from the center of said measuring electrode, means for applying said measuring and screening electrodes onto the surface of said display window remote from said color selection electrode near one corner of said window such that said centers of said screening and measuring electrodes lie substantially on a diagonal line extending from said one corner to an opposite corner of said window to thereby form a capacitor defined by said color selection electrode and said measuring electrode, and means for applying an alternating voltage to said measuring electrode.
Dependencies are inferred from the claim text.