Oscilloscope
An oscilloscope is a widely used electronic measuring instrument . It can invisible electrical signal is converted into a visible image, to facilitate the changing process of various people study electrical phenomenon. The oscilloscope uses a narrow, high-speed electron beam to create a tiny spot on a phosphor- coated screen. Under the effect of the measured signal, if the electron beam of a pen tip, the curve can be drawn instantaneous value of the signal at the screen surface. Observed various waveform plot signal amplitude versus time using an oscilloscope, it may also be used to test a variety of different amounts of power, such as voltage, current, frequency, phase, amplitude modulation and the like.
Display circuit
The display circuit includes two parts of an oscilloscope and its control circuit. The oscilloscope is a special type of electron tube and an important component of the oscilloscope .
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Minute. 3 by the CRT electron-gun, deflection system and a fluorescent screen components.
( 1 ) electron gun
And an electron gun for generating a high velocity, an electron stream bunching, to collide with the fluorescent screen to emit light. It is mainly composed of a filament F , a cathode K , a gate electrode G , a first anode A1 , and a second anode A2 . Except for the filament, the remaining electrodes are constructed of metal cylinders and their axes are maintained on the same axis. After the cathode is heated, electrons can be emitted in the axial direction; and a control electrode is a negative potential relative to the cathode, the potential change can be varied by controlling the number of electrons very small holes, i.e. control the brightness of the spot on the phosphor screen. In order to increase the brightness of the light spot on the screen, without reducing the sensitivity of electron beam deflection, modern CRT, the phosphor screen between the deflection yoke and further adding a post acceleration electrode A3.
The first anode adds a positive voltage of about several hundred volts to the cathode. A positive voltage is applied to the second anode that is higher than the first anode. The electron beam passing through the control micro-hole is accelerated by the high potential of the first anode and the second anode, and is moved at a high speed in the direction of the phosphor screen. Due to the homogeneity of the charge, the electron beam will gradually spread out. By focusing the electric field between the first anode and the second anode, the electrons are re-aggregated and merged at one point. By properly controlling the magnitude of the potential difference between the first anode and the second anode, the focus can just fall on the screen, revealing a bright and small dot. Changing the potential difference between the first anode and the second anode can adjust the focus of the spot, which is the principle of the " focus " and " assist focus " adjustment of the oscilloscope. The first electrode is Sanyang CRT coated graphite inner cone is formed, a high voltage is usually applied, it has three functions: â‘ after passing through the deflection system is further accelerated electrons, the electrons have enough energy To bombard the screen to obtain sufficient brightness; 2 graphite layer coated on the entire cone, can play a shielding role; 3 electron beam bombardment of the screen will produce secondary electrons , A3 at high potential can absorb these electrons.
·                                 (2) deflection system
The deflection system of the oscilloscope is mostly electrostatically deflected. It consists of two pairs of mutually parallel parallel metal plates, called horizontal deflection plates and vertical deflection plates. Control the movement of the electron beam in the horizontal and vertical directions, respectively. When electrons move between the deflection plates, if no voltage is applied to the deflection plates, there is no electric field between the deflection plates, and electrons entering the deflection system after leaving the second anode will move axially toward the center of the screen. If there is a voltage on the deflection plate, there is an electric field between the deflection plates, and electrons entering the deflection system will be directed to the designated position of the phosphor screen by the deflection electric field.
If the two deflecting plates are parallel to each other and their potential difference is equal to zero, the electron beam having the velocity Ï… passing through the deflecting plate space moves along the original direction (set as the axial direction) and hits the coordinate origin of the fluorescent screen. . If there is a constant potential difference between the two deflecting plates, an electric field is formed between the deflecting plates. This electric field is perpendicular to the direction of movement of the electrons, so that the electrons are deflected toward the deflecting plate having a relatively high potential. Thus, in the space between the two deflecting plates, the electrons are tangentially moved along the parabola at this point. Finally, the electron landing point on the phosphor screen A, the screen A from the origin point (0) there is a distance, this distance is called the amount of deflection is represented by y. Y Vy is proportional to the amount of deflection applied voltage deflection plates. Similarly, when a DC voltage is applied to the horizontal deflection plate, a similar situation occurs, except that the spot is deflected in the horizontal direction.
( 3 ) fluorescent screen
Oscilloscope physical map
The screen is located at the end of the oscilloscope and its function is to display the deflected electron beam for viewing. The illuminating screen of the oscilloscope is coated with a layer of luminescent material, so that the fluorescent screen exhibits fluorescence at the point of high-speed electron impact. The brightness of the spot at this time is determined by the number, density, and speed of the electron beams. When the voltage of the gate is changed, the number of electrons in the electron beam will change and the brightness of the spot will change. When using an oscilloscope, it is not advisable to allow a very bright spot to be fixed at a position on the oscilloscope screen. Otherwise, the phosphor will burn out due to long-term electron impact and lose its ability to emit light.
Fluorescent screens coated with different fluorescent substances will show different colors and different afterglow times when subjected to electron impact. Usually, the general signal waveform is used to observe green light. It is a medium afterglow oscilloscope tube for observation.
The periodic and low-frequency signals are made of orange-yellow light, which is a long afterglow oscilloscope; for oscilloscopes used for photography, the short-lasting oscillating wave tube with blue color is generally used.
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