Storage Tube, Visual

an electron tube used to record, store, and subsequently reproduce on a phosphor screen information received as electric signals at the input electrode of the instrument. The writing electron beam of the tube is modulated by the signal to be recorded (Figure 1). The beam, in moving over the target, displaces secondary electrons from the target’s dielectric surface and generates a variable potential on this surface. The variations in potential are proportional to the intensity and duration of the beam.

The charge pattern that is produced on the target modulates the reading electron beam, which produces an image on the screen. In halftone storage tubes, the potential of the target is negative with respect to the cathode potential of the reading beam’s electron gun. For this reason, the electrons of the reading beam do not hit the target and the recorded image is preserved on the target for up to several minutes. In bistable storage tubes, the potential of the target is positive with respect to the cathode potential of the gun, and the reading beam brings the target potential to two stable values. Here, the image can be preserved for up to several hours.

Figure 1. Schematic diagram of a visual storage tube: (1) phosphor screen, (2) target of fine-mesh screen covered with a layer of dielectric substance, (3) storage layer, (4) electrode controlling the reading beam of electrons, (5) reading beam of electrons uniformly bombarding the surface of the target, (6) electron gun producing the reading beam, (7) writing beam, (8) deflecting system of the writing beam, (9) electrode receiving the writing signal, (10) electron gun producing the writing beam

Visual storage tubes are used for observation of momentary or rarely repeated signals in, for example, oscillographs, radar screens, and data output devices of electronic computers. In oscillographs, the luminous intensity of storage tubes is between 2 and 150 candles per square meter. The resolution, determined by the number of lines across either the diameter or any side of the image on the screen, is between 60 and 200. The reproduction time is from 1 to 600 minutes. For storage tubes used in radar equipment, these figures are, respectively, 100–5,000 candles per square meter, 150–600 lines, and 0.2–2.0 minutes.

The term “storage tube” can be applied to any cathode-ray storage tube. Since the 1970’s, the latter term has come to be preferred.