Laboratory_1

Laboratory_1 - PRINCETON UNIVERSITY Laboratory 1:...

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PRINCETON UNIVERSITY PHYSICS 106 LAB Laboratory 1: Introduction to the Oscilloscope Introduction. Two workhorses in any R&D lab are the signal generator and the oscilloscope. A signal generator is used to create a periodic voltage, which may be used as the input to some experimental apparatus. The oscilloscope is used to measure voltage as a function of time, often the output of some apparatus. (Actually, it is more typically used to measure a signal in the middle of some apparatus that isn’t quite working right….) Modern oscilloscopes are completely digital--computers in disguise--except for the analog front end amplifiers and the cathode ray tube (CRT). Nevertheless, a well-designed scope still retains the look and feel of the analog scopes of days gone by. For most instruments, the best way to get proficient is to 1) understand the basic principles, 2) break it down (in your mind) into functional units, and 3) play with it. Be sure that each person in a lab group does some of the oscilloscope work. You will use the oscilloscope in more labs this semester, so getting familiar with it now will save you a lot of time later. Basic Principles of the oscilloscope. The sketch below shows a block diagram of an oscilloscope. The cathode-ray tube (CRT) is the central element. It's very similar to the one in a TV set or a computer monitor. The electron gun forms a narrow beam of electrons which passes through two sets of deflection plates on its way to a phosphorescent screen. The screen emits light where the beam hits. The horizontal and vertical amplifiers apply voltages to the deflection plates. The resulting E fields from these voltages deflect the beam to any position on the screen. Thus, a saw-tooth voltage on the horizontal plates causes the spot to sweep at a constant speed from left to right across the screen making the horizontal position proportional to time. If simultaneously there is a vertical voltage of (say) V 0 sin2 π t/T, a sine wave will be drawn on the screen. But there's a catch. Unless the saw-tooth and the sine voltage are synchronized , successive wave forms will not be superimposed on the screen. That's the job of the trigger circuit. When on 'internal' it starts each saw-tooth sweep at the same voltage level of the vertical signal, thus the two are synched and the pattern on the screen is stationary. Sometimes you want to trigger from an external (reference) signal, or even from the 60 Hz power line; a switch lets you do that. Oscilloscope cut-away box drawing
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This note was uploaded on 05/04/2010 for the course PHY 106 taught by Professor Roberth.austin,hermanl.verlinde during the Spring '08 term at Princeton.

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Laboratory_1 - PRINCETON UNIVERSITY Laboratory 1:...

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