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LAB# 24 THE CATHODE RAY OSCILLOSCOPE INTRODUCTION : One of the most basic instruments for all modern science and technology is the cathode ray oscilloscope (C R O) or scope. The purpose of this experiment is twofold: (1) teach you how to use a CRO and a function generator; (2) how to use a CRO to analyze waves. In particular, several different sources will be displayed and compared by means of the CRO. The heart of the CRO is simply an evacuated tube very similar to a television picture tube. The instrument we will use has two sets of deflecting plates, so that the beam of electrons can move either from side to side (x- deflection) or up and down (y-deflection). See figure 1. Figure 1 The Oscilloscope That's basically all there is to an oscilloscope. There is a special circuit (called the sweep) which automatically increases the voltage on the horizontal plates until the spot moves across the screen from left to right and then quickly switches back to zero voltage and repeats itself. You can "sweep" the beam across at fast (100,000 times/sec.) or slow (10 times/sec.) speeds so you can get a good picture of the vertical signal. In addition, there are amplifiers to make the signal larger and move it on the screen, but that does not concern us right now. APPARATUS: Oscilloscope or scope, Two digital function generators or oscillators, microphone, stands, probes and connectors, tuning fork, and if available (Computer tutorial “OSCILLOSCOPE”). PROCEDURE: PART 1. Producing and Measuring Sine Waves 1. Start with nothing plugged into the oscilloscope. 2. Turn on the oscilloscope and wait about 30 sec. Use the vertical and horizontal POSITION knobs as necessary to bring the trace to the center of the screen. 3. Adjust the trace intensity and brightness so that the trace is easily visible.
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4. Some knobs are printed with the word CAL’D , turn them fully clockwise. These are calibration knobs. On the VOLTS/DIV (volts per division) knobs, the outer
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