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The use of cathode ray tube


The use of cathode ray tube

Cathode-ray tubes used in oscilloscopes to measure voltages and phase angles, analysis of the curve of current or voltage and t. d. These tubes are used in television and radar installations.

Cathode ray tube there are different types of. By way of generating the electron beam, they are divided into tube with a cold cathode and glowing. Tube with a cold cathode are used relatively rarely, because their work requires a very high voltage (30-70 kV). Tubes with a glowing cathode are widely used. These tubes in the control method of the electronic beam is also divided into two types: electrostatic and magnetic. In the electrostatic tubes control electron beam by using an electric field, but in magnetic materials using a magnetic field.

Cathode ray tube with electrostatic control used in oscilloscopes and are extremely diverse in design implementation. It helps to familiarize students with principle of operation of such a tube, contains the main model elements. These goals meets the tube type 13ЛОЗ7, which is presented on the table with some simplifications.

A cathode-ray tube is a well-vacuumed glass bottle, inside which are the electrodes. The wide end of the tube is the screen — the inner side is covered with a fluorescent substance. The substance of the screen glows when the electrons strikes. The source of electrons is a cathode of indirect filament. The cathode consists of a filament 7, inserted in a thin porcelain tube (insulator), wearing a cylinder 6 with oxide finish end (the cathode), which results in the emission of electrons in one direction only. Emitted from the cathode, the electrons rush to the anode 4 and 3, having quite a high potential relative to the cathode (several hundred volts). To give the electron beam the beam shape and focusing on the screen the beam passes through a series of electrodes. However, you should pay attention to teaching-students only three electrodes: modulator (the control cylinder) 5, the first anode 4 and the second anode 3. The modulator consists of a tubular electrode, to which is supplied a negative potential relative to the cathode. Thanks to it passing through the modulator the electron beam will be pulled together into a narrow beam (ray) and directed by the electric field through the opening in the anode towards the screen. Increasing or decreasing the potential of the control electrode, you can adjust the number of electrons in the beam, t. e. the intensity (brightness) the glow of the screen. With the help of the anodes not only creates an accelerating field (provides acceleration of electrons), but, by changing the potential of one of them, more accurately focusing the electron beam on the screen and to get the most sharpness of the luminous point. Usually the focusing is performed by changing the potential of the first anode, called focusing.

The electron beam, coming out of the holes in the anode, passes between the two pairs of deflecting plates 1,2 and hits the screen, making it glow.

Applying voltage to deflecting plates, it is possible to cause the deflection of the beam and the displacement of the luminous spot from the center of the screen. The magnitude and direction of bias depend on the voltage, served on plate, and the polarity of the plates. The table shows the case, when the voltage is applied only on vertical plate 2. At the indicated polarity of the plates the displacement of the electron beam under the action of an electric field is to the right. If apply voltage on th-izontally plate 1, the displacement of the beam will occur in the vertical direction.

In the lower part of the table method of beam control using a magnetic field, created by two mutually perpendicular coils (each coil is divided into two sections), the axes of which are vertical and horizontal directions. The table shows the case, when in the horizontal coil current is absent and the vertical coil provides the displacement of the beam only in the horizontal direction.

The magnetic field of the horizontal coil causes the displacement of the beam in the vertical direction. The combined action of the magnetic fields of two coils to enable movement of the beam across the screen.

Magnetic tubes are used in TVs.

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