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01B - 1B THE OSCILLOSCOPE Introduction The oscilloscope is...

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7/29/2008 P109 Lab1B - 1 - 1B: THE OSCILLOSCOPE Introduction The oscilloscope is a universal measuring instrument with applications in physics, biology, chemistry, medicine, and many other scientific and technological areas. It is used to give a visual representation of electrical voltages. Thus, any quantity which can be converted to a voltage can be displayed on an oscilloscope. Although the oscilloscope looks very complicated, once you familiarize yourself with its controls and functions, it is surprisingly easy to use. The purpose of this experiment is to develop familiarity with the oscilloscope and with the types of measurements that can be made with it. How the Oscilloscope Works The most important component of the oscilloscope is the cathode ray tube (CRT), a vacuum tube in which a filament is heated to “boil off” electrons which are then focused into a beam and “shot” toward the screen with an electron gun. In the photograph above, screen is the rectangular, gridded area on the left of the oscilloscope. The screen is coated with fluorescent material which glows when it is hit by the electron beam. On its way to the screen, the beam passes between two sets of deflection plates (horizontal and vertical) and a voltage applied to these plates will cause the beam to curve. The sketch illustrates the CRT components with a negative voltage applied only to the vertical plates ( V y ), causing the beam to bend downward. The amount of deflection d shown on the screen is proportional to the voltage applied to the plates, so you can measure a voltage by seeing where the beam hits the screen. Glass Tube Fluorescent Screen Electron Gun Filament d V y V x The oscilloscope you are using has many electronic refinements associated with the CRT to allow electronic signals to be conveniently displayed and measured. The following sections describe these controls and tell you how to get the oscilloscope ready for the experiment.
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P109 Lab 1B - 2 - Getting Started Look at all those knobs! Looks complicated, doesn't it? Relax. Prepare to enjoy this. We tell you step by step how to work the scope and the function generator. It really isn't as bad as it looks. As you work through this experiment, feel free to twiddle the knobs as much as you want. As long as you don't wrench them off their shafts, there are NO control settings that will harm the equipment or endanger you. On the next page is a drawing of the scope with the controls labeled using circled numbers. As much as possible, controls have been paired. For example, numbers 5A, 6A, 7A etc. control the same functions for channel 1 (CH1) as numbers 5B, 6B, 7B etc. control for channel 2 (CH2). Note that the scope is divided into four major areas, the SCREEN area on the left, the VERTICAL section, in the middle, the Horizontal section and the TRIGGER section on the right. We will look what the controls for each of these sections do, one at a time. Don’t worry if you can’t remember everything.
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