Cathode Ray Tube CRT l The electrons are

Cathode Ray Tube (CRT) l The electrons are deflected in various directions by two sets of plates. l The placing of charge on the plates creates the electric field between the plates and allows the beam to be steered. l Commonly used to obtain a visual display of electronic information in oscilloscopes, radar systems, televisions, etc. . l Be a vacuum tube in which a beam of electrons is accelerated and deflected under the influence of electric or magnetic fields.

Cathode Ray Tube (CRT) - is one of the main elements of an oscilloscope. l A CRT is commonly used to obtain a visual display of electronic information in oscilloscopes, radar systems, televisions, etc. l The CRT is a vacuum tube in which a beam of electrons is accelerated and deflected under the influence of electric or magnetic fields. l The tubes are produced with electrostatic and electromagnetic control, where electrostatic or magnetic fields deviate the electron beam respectively. l The principle scheme of CRT has electrostatic control as well as the motion of the electrons in the beam drawing a sinusoid on the screen of oscilloscope.

Configuration of CRT l CRT consists of 6 sections: 1. Glass bulb evacuated to a high vacuum (真空管) 2. Cathode (a source of electrons，電子槍陰極) 3. Cathode heater (陰極加熱 器) 4. Electrodes for brightness and focus control, several accelerating anodes (亮度、 聚焦、加速控制柵極) 5. Pairs of horizontal and vertical capacitor plates deviating the electron beam

Discharge Tube l It was observed that whenever the glass tube filled with air at low pressure and l sealed with electrodes at both the ends was subjected to about 10, 000 volts of electricity, l a strange glow was produced around the edges of the wide end of the glass tube, irrespective of the type of gases present in it. l The glass tube with sealed electrodes is called discharge tube. Discharge Tube Electron Gun

Cutaway rendering of a color CRT 1. Electron guns 2. Electron beams 3. Focusing coils 4. Deflection coils 5. Anode connection 6. Mask for separating beams for red, green, and blue part of displayed image 7. Phosphor layer with red, green, and blue zones 8. Close-up of the phosphor-coated inner side of the screen

CATHODE-RAY TUBE (CRT) - is one of the main elements of an oscilloscope. l One of anodes, which accelerate the electrons, is placed close to the screen. l The high positive voltage is applied to this electrode. l Under the action of the applied voltage the electrons are moved with acceleration from cathode to anode. l In the absence of the voltage applied to deviating plates of the capacitor the electron beam will be incident on the screen in the center brightening a point in the fluorescing layer. l In oscilloscope the analyzed signal after amplification is applied to vertical deviating plates, while the periodic sawtooth signal is applied to horizontal plates.

http: //physicsanimations. com/Physics/English/osc _tmp. htm l As a result the electron beam "draws" the dependence of the investigated signal on time on the screen of the tube. l Reaching the right side of the screen the beam has to be returned to an initial point at the left side. l Thus, if CRT is not blanked during this retrace, then the beam will leave a track crossing the image of investigated signal. l For this reason, during retrace a negative voltage is applied to control electrode situated near to cathode and electrons are locked by such a way at the electron gun. l As a result, the electron beam will be discontinuous, as shown in animation.

Related Web Sites for CRT Animation l http: //highered. mcgraw- hill. com/sites/0072512644/student_view 0/chapter 2/ani mations_center. html l http: //physics- animations. com/Physics/English/osc_tmp. htm l http: //www. sciencemuseum. org. uk/on- line/electron/section 2/shockwave 2. asp l The Cathode Ray Tube site: http: //members. chello. nl/~h. dijkstra 19/page 3. html l How Television Works: http: //www. howstuffworks. com/tv. htm/printable

示波器正面: (例) TRIO CS-1022 Y -X (3 -2) l Z l T

2. 垂直(vertical)(Y軸)及水平(horrizontal)(X軸)控制 (以Y為例) 軌跡位置(position) (1) 垂直位置 (拉出時放大十倍) 可變/校正控制(variable/cal) (2) 轉到校正(cal)位置, 靈敏度範圍: 1 m. V/格 – 5 V/格 靈敏度(sensitivity/volts) (3) 信號放大及衰減 輸入模式(ac-GND-dc) (4) ac: alternating coupling (交流) GND: no signal (校正基線) dc: direct coupling (交流+直流) 輸入(input) (5) BNC型插座 控制模式 (mode) (12) ch 1: Y signal only ch 2: X signal only add: X+Y alt, chop (其它用途) (3 -3)

示波器方塊圖(block diagram): (例) National VP-5107 T Y X/ T (3 -5) calibrator power/Z

交流信號產生器(signal generator) (例) TRIO AG-203 電源(power) (1, 2) (保護儀器) 輸出衰減(attenuation): 0 - -50 d. B 6個衰減級距 (3) I(d. B) = 10. log 10(I/I 0) 0 d. B =1, -10 d. B = 10 -1 -20 d. B = 10 -2, -30 d. B = 10 -3 -40 d. B = 10 -4, -50 d. B = 10 -5 信號輸出(output) (4) 波型(wave form): 正弦波, 方波 (5) 頻率(frequency): 10 Hz – 1 MHz 5個頻率級距(range) (6, 8, 9, 10) x 1 (10 -100 Hz), x 100 x 1 k, x 10 k (100 k. Hz – 1 MHz) 振幅(amplitude): 連續調整 (7) (3 -6)