He observed that some unknown rays were emitted from the cathode negative electrode which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines. InArthur Schuster demonstrated cathode rays could be deflected by electric fieldsand William Crookes showed they could be deflected by magnetic fields. Thomson succeeded in measuring the mass of cathode rays, showing that they consisted of negatively charged particles smaller than atoms, the first " subatomic particles ", which were later named electrons.
He observed that some unknown rays were emitted from the cathode negative electrode which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines.
InArthur Schuster demonstrated cathode rays could be deflected by electric fieldsand William Crookes showed they could be deflected by magnetic fields. Thomson succeeded in measuring the mass of cathode rays, showing that they consisted of negatively charged particles smaller than atoms, the first " subatomic particles ", which were later named electrons.
The first cathode-ray tube to use a hot cathode was developed by John B. Johnson who gave his name to the term Johnson noise and Harry Weiner Weinhart of Western Electricand became a commercial product in Zworykin who was influenced by Takayanagi's earlier work.
The beam is deflected horizontally by applying an electric field between a pair of plates to its left and right, and vertically by applying an electric field to plates above and below. Televisions use magnetic rather than electrostatic deflection because the deflection plates obstruct the beam when the deflection angle is as large as is required for tubes that are relatively short for their size.
Phosphor persistence[ edit ] Various phosphors are available depending upon the needs of the measurement or display application. The brightness, color, and persistence of the illumination depends upon the type of phosphor used on the CRT screen.
Phosphors are available with persistences ranging from less than one microsecond to several seconds. For events which are fast and repetitive, or high frequency, a short-persistence phosphor is generally preferable. Oscilloscope CRTs designed for very fast signals can give a brighter display by passing the electron beam through a micro-channel plate just before it reaches the screen.
Through the phenomenon of secondary emissionthis plate multiplies the number of electrons reaching the phosphor screen, giving a significant improvement in writing rate brightness and improved sensitivity and spot size as well.
The graticule may be permanently marked inside the face of the CRT, or it may be a transparent external plate made of glass or acrylic plastic. An internal graticule eliminates parallax errorbut cannot be changed to accommodate different types of measurements.
These are distinct from digital storage oscilloscopes which rely on solid state digital memory to store the image. Where a single brief event is monitored by an oscilloscope, such an event will be displayed by a conventional tube only while it actually occurs. The use of a long persistence phosphor may allow the image to be observed after the event, but only for a few seconds at best.
This limitation can be overcome by the use of a direct view storage cathode-ray tube storage tube. A storage tube will continue to display the event after it has occurred until such time as it is erased. A storage tube is similar to a conventional tube except that it is equipped with a metal grid coated with a dielectric layer located immediately behind the phosphor screen.
An externally applied voltage to the mesh initially ensures that the whole mesh is at a constant potential. This mesh is constantly exposed to a low velocity electron beam from a 'flood gun' which operates independently of the main gun. This flood gun is not deflected like the main gun but constantly 'illuminates' the whole of the storage mesh.
The initial charge on the storage mesh is such as to repel the electrons from the flood gun which are prevented from striking the phosphor screen. When the main electron gun writes an image to the screen, the energy in the main beam is sufficient to create a 'potential relief' on the storage mesh.
The areas where this relief is created no longer repel the electrons from the flood gun which now pass through the mesh and illuminate the phosphor screen. Consequently, the image that was briefly traced out by the main gun continues to be displayed after it has occurred.
The image can be 'erased' by resupplying the external voltage to the mesh restoring its constant potential. The time for which the image can be displayed was limited because, in practice, the flood gun slowly neutralises the charge on the storage mesh. One way of allowing the image to be retained for longer is temporarily to turn off the flood gun.
It is then possible for the image to be retained for several days. The majority of storage tubes allow for a lower voltage to be applied to the storage mesh which slowly restores the initial charge state.
By varying this voltage a variable persistence is obtained. Turning off the flood gun and the voltage supply to the storage mesh allows such a tube to operate as a conventional oscilloscope tube. Williams tube The Williams tube or Williams-Kilburn tube was a cathode-ray tube used to electronically store binary data.
It was used in computers of the s as a random-access digital storage device. In contrast to other CRTs in this article, the Williams tube was not a display device, and in fact could not be viewed since a metal plate covered its screen.
Magnified view of a delta-gun shadow mask color CRT Magnified view of a Trinitron color CRT Spectra of constituent blue, green and red phosphors in a common CRT Color tubes use three different phosphors which emit red, green, and blue light respectively.
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