21-01-2013, 03:26 PM
Cathode Ray Oscilloscope
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Learning Objectives:
During this lab, you will
1. learn how to measure time-varying electronic signals with a cathode ray oscilloscope (CRO).
2. estimate the uncertainty in measure-ments made with a CRO and estimate the uncertainty in a quantities that are calculated from quantities that are uncertain.
Introduction
The cathode ray oscilloscope, CRO or simply scope, is used in many fields of basic and applied research and in electronics development and repair. It is generally the tool of choice for examining signals that change with time on a scale of 1 second to 1 nanosecond. The sketch of the scope in Figure 1 includes a triangular wave signal, a voltage that, as a function of time, continu-ally (and linearly) ramps up and down between two limiting voltages.
Measurements of a Sine Wave
You have been looking at a square wave. Another common signal is a sine wave [V = V0sin(ωt + φ)] such as the 110-volt AC power line. You will use a doorbell trans-former to reduce the signal to a safer level.
Connect the center and either one of the two outer terminals of the transformer to the CH 1 input of the oscilloscope. Adjust the sweep time, the vertical sensitivity and other controls until you get a stable picture. (It probably won’t be a very good sine wave, but that’s what you often have at an outlet.) Sketch the waveform (don’t forget to label the scales on your sketch). Measure and record the period and calculate the frequency. Measure and record the peak-to-peak voltage of the signal.