Design and Operation of a Cathode-Ray Oscillograph for External Photography

Citation

Hawley, Paul Frederick (1937) Design and Operation of a Cathode-Ray Oscillograph for External Photography. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jvh3-bq94. https://resolver.caltech.edu/CaltechTHESIS:05232024-215513766

Abstract

The prominent features in the design of the instrument are discussed. Novel among these are the design of the metal discharge tube, Lenard window and associated apparatus, and the time sweep and blocking circuits. Investigation of the metal discharge tube showed that there was an optimum spacing between cathode and anode, that decreasing the diameter of the tube increased the ratio of beam current to cathode current, and that raising the cathode voltage increased the current density in the beam. A 2½ x 3½ inch Lenard window using cellophane foil supported by a metal grid is used, and has proved to be quite satisfactory and durable. The sweep and blocking circuits are integral, operating from a triple sphere gap, and are so arranged that the beam sweeps clear across the window without any auxiliary biasing arrangement. Tripping is either automatic from an incoming surge, or semi-manual from a second set of gaps set to trip at convenient intervals. A number of sweep speeds are available, controlled by a selector switch.

The various factors involved in Lenard photography are tabulated and the majority are investigated. The radial current density in the recording spot is measured, and the effects of changes in discharge tube design in this regard are evaluated. Several types of films were tested to find the most sensitive. Eastman Process Nitrate film was finally adopted as sensitive as most and mechanically superior to the others. The best development time to use for typical oscillograms in several developers was determined. From a photometric investigation of oscillograms taken with a wide range of velocities and cathode voltages, the blackening of this film by cathode rays was established as a function of incident charge density and cathode voltage. An empirical formula B = K √q is found to express the blackening as a function of charge density for a given cathode voltage. From these data the maximum recording speed is computed to be 30,000 km./sec.

Operating experience with the tube is given. Typical osoillograms illustrating automatic recording of surge phenomena, etc., are shown. Various types of distortion encountered in operation are illustrated, and methods for eliminating them are given.

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