Oscilloscope Essay

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Physics Department Kuwait University February, 2001 EXP. NINE Course 127 Cathode-ray Oscilloscope (CRO) Objective • To introduce the basic structure of a cathode-ray Oscilloscope. • To get familiar with the use of different control switches of the device. • To visualize an ac signal, measure the amplitude and the frequency. Theory Cathode-ray Oscilloscope The device consists mainly of a vacuum tube which contains a cathode, anode, grid, X&Y-plates, and a fluorescent screen (see Figure below). When the cathode is heated (by Fluorescent screen Electron gun Deflection plates Cathode Anode Y-plates Electron beam Grid X-plates Figure 1: The basic structure of a CRO applying a small potential difference across its terminals), it emits electrons. Having a potential difference between the cathode and the anode (electrodes), accelerate the 42 emitted electrons towards the anode, forming an electron beam, which passes to fall on the screen. When the fast electron beam strikes the fluorescent screen, a bright visible spot is produced. The grid, which is situated between the electrodes, controls the amount of electrons passing through it thereby controlling the intensity of the electron beam. The X&Y-plates, are responsible for deflecting the electron beam horizontally and vertically. A sweep generator is connected to the X-plates, which moves the bright spot horizontally across the screen and repeats that at a certain frequency as the source of the signal. The voltage to be studied is applied to the Y-plates. The combined sweep and Yvoltages produce a graph showing the variation of voltage with time, as shown in Fig. 2. Front panel The front panel of the CRO is shown in Fig. 2. Power The trace Intensity X-posit. Time/Div Focus Y-posit. Y-posit. Volt/Div X-mag Ch1 Volt/Div Ch2 Figure 2: The front panel of the CRO Alternating

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