PHY 2049L
Lab 5

Oscilloscope Use

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Updated: 1/1/2009
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Comment

This page is fairly complete, but there is no substitute for looking at and fiddling with the real thing. That is, in fact, the main reason for doing this lab. You can only learn this by a "hands on" learn-by-doing experience.


Controls

The function generator is on top.
This one is set with the "100" button pushed in and the dial set to about the 2.0 multiplier so it produces a frequency of 200 Hz as measured by the frequency counter. (See photo at bottom of page.) A coax cable is used to connect its output (which is at the max amplitude for 20V peak-to-peak) to the oscilloscope.

closeup of oscilloscope controls and function generator

The oscilloscope is set to 5 V per division vertically using dial 12 (see below) for Channel 1 (hence amplitude of wave is about 10 V), and 1 ms per division horizontally using dial 18 (hence period of wave is about 5 ms). The trigger level (dial 23) is set to zero with positive slope (switch 22). See diagram below for other details.

Knobs 1 and 3 are used to give a bright, sharp trace that you can read clearly. (Button 2 is used to shrink the trace if you need help finding it so you can adjust the position vertically or horizontally.)

We will only use Channel 1 (CH 1) for the vertical trace. These controls are all in the second column. You need to be sure that switch 14 is to the left (AC), that switch 9 is to the left (CH 1), and that switch 10 is to the left (NORM). You use knob 12 to select the voltage per division vertically. You use knob 7 to position the trace vertically on the screen; this is a critical adjustment for reading the zero crossing when determining a frequency.

labeled diagram of oscilloscope

The fourth column contains the controls for the horizontal trace, which we will use as a time reference. You need to be sure knob 19 is fully clockwise and switch 17 is to the left so the frequency is at the calibrated value: then knob 18 sets the time per division. You use 16 to position the trace horizontally on the screen.

The last column controls when the trace is triggered. We will leave the 24, 25, and 27 selectors alone, triggering on CH 1 under conditions set by knobs 22 and 23.

The photo below shows an additional closeup of the control panel so you can compare it to the diagram above.

oscilloscope controls

This is set to 2 V per division vertically for CH 1, the same for CH 2, and 2 ms per division for the horizontal time scale. The trigger is selected from CH 1, starting when the slope is positive.


Full Lab Setup

This picture shows the full arrangement, with a coax cable connecting the 200 Hz signal (here a triangular wave) from the function generator to the oscilloscope (below) and frequency counter (above) while an adapter at the frequency counter splits off a signal to go to an AC voltmeter (left).

setup with wave generator producing triangular wave

You might notice that the AC voltmeter has a different reading than it did for a sine wave with the same amplitude. You will explore this (which results from the rms averaging done by the voltmeter in AC mode) during the lab. Remember to check if you have a sine wave or some other kind of wave when using the signal generator in later labs. Changing the shape of the wave has significant effects!

 
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