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Oscilloscope

# Oscilloscope - PHY 132 LAB Oscilloscope Introduction In...

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PHY 132 LAB : Oscilloscope Introduction In this lab, we consider AC signals, and use of the oscilloscope. This material is out of sequence with PHY131, but the concepts are not difficult. Text Reference: Young & Freedman 26.1. The oscilloscope (scope) is an indispensable tool for measuring electrical signals. It gives a display of voltage (vertical) vs. time (horizontal). These scales are accurately calibrated, so you can obtain numbers from the display. There are a zillion knobs, most of which we can ignore for now. You do need to understand the following: 1. Gain and position of Y and X axes. These are marked as volts/division and sec/division. 1 division is a 1cm box on the screen. A value is determined from the display as volts = (# divisions) * (volts/division). You can generally read this to 0.1 division. Take care that the CAL knobs are clicked into the calibrated position. 2. Input coupling : A/C or D/C or GND. D/C feeds the signal directly into the scope. A/C feeds only the A/C part after stripping the average (D/C) value. GND shorts the input providing an accurate zero reference, for positioning the display. 3. Focus/Intensity : adjust these to get a clear sharp line, but don’t burn the screen. Wiring tips and Digital Multimeters: See notes appended. Theory: AC signals frequently take the form of a sinewave, which we write as v(t)=V 0 sin( ω t) + V DC eq. 1 This has amplitude V 0 , and angular frequency defined as ω = 2 π /T = 2 π f eq. 2 where T is the period (sec) and “f” is the frequency, in cycles per second or Hertz (Hz). It is possible also to have a DC offset V DC . PHY132 Labs (Bennett, JCHS) -1- 08/21/06

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