User:Alex G. Benedict/Notebook/Physics 307L: Junior Lab/Oscilloscope Lab

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Oscilloscope Lab

This Lab was performed by myself and my partner, Joseph Frye User:Joseph_Frye, on August 23 and 30th.

SJK 16:20, 24 September 2010 (EDT)
16:20, 24 September 2010 (EDT)
This is a good primary notebook, but in general it's a little sparse. I tried to find your notes for the neon lab, but can't see any yet. So, I'm guessing you're taking notes with another application. I'm hoping they're a bit more detailed than these, especially since you and Joe broke ground on that experiment.

Set Up

SJK 15:59, 24 September 2010 (EDT)
15:59, 24 September 2010 (EDT)
Good listing of equipment make and model numbers. Pictures would help for explaining connections.

To set up for this lab, we got an oscilloscope and function generator from the equipment closet, and we got BNC cables from the holders on the side of the same closet. We then plugged in the equipment, both of the power cords into the power strip in the table, and one of the BNC cables from the low voltage out on the function generator to the CH 1 in on the Oscilloscope.

Equipment:Tektronix TDS 1002 oscilloscope,BK Precision 4017A 10MHz sweep/function generator

Waveform Measurement

We measured the peak to peak voltage, and the frequency by the three methods suggested in the lab book, we performed three trials for each measurement. The data for the three trials is below.

{{#widget:Google Spreadsheet |key=0AsLE8iWrtjlSdFdsNkhhSGFzcUZlY0ZTcHpLaEpmTkE |width=1050 |height=200 }}

We discovered during the lab, that the Ranges provided on the back of the oscilloscopeSJK 16:04, 24 September 2010 (EDT)
16:04, 24 September 2010 (EDT)
Are you sure these ranges refer to the oscilloscopes ability to measure input signals? I think these ranges are the acceptable range of power supplies. For example the roughly 60 Hz, 120V outlet you used. For sure, the scope can measure input signals much higher than 440Hz
45-440Hz for 100-120V, 45-66Hz for 120-240V, were accurate for the frequencies and voltages it could measure, as it failed for frequencies which were much smaller than 45Hz, and for frequencies much larger than 440Hz, and with a DC offset much larger than 120V it could not measure accurately outside a narrow range of frequencies.


We discovered that the Triggering function when set to rising, stops the graph from changing when it encounters a rising voltage, when set to falling, it would move until it encountered a falling voltage, and then stop. The pulse setting was much like the rising and falling triggers,I think it may stabilize the graph based on when it encounters a full period of the wave or something. The video trigger did not seem to settle,and we were not sure what it measured. SJK 16:06, 24 September 2010 (EDT)
16:06, 24 September 2010 (EDT)
"video" trigger is designed for signals from /to video monitors, for example NTSC signals. The pulse is good for triggering when the level stays above or below a set level for a certain amount of time.

AC Coupling

The AC Coupling seems to remove any constant voltage offset. The AC coupling is better for observing changes to the voltage if it is mostly large and changes are small compared with the offset.

When applied to the square wave graph, it produced a curve like a decaying exponential.

When measuring the fall time, it seemed to vary with the frequency of the square wave produced by the function generator. The data from a few trials is below. We wrote the frequency of the measurements next to the trial number. The expected RC constant varies for each measurement, since the expected fall time is from t=0.34/BW where BW is the bandwidth in hertz, which we took to be the frequency of the generated wave.

Data on Sheet 2. {{#widget:Google Spreadsheet |key=0AsLE8iWrtjlSdFdsNkhhSGFzcUZlY0ZTcHpLaEpmTkE |width=1150 |height=400 }}

Our observed values were pretty close to the expected value of the RC constants, the mean relative error of the four measurements was about 0.14 for both measurement by cursor and by the measure function.

SJK 16:12, 24 September 2010 (EDT)
16:12, 24 September 2010 (EDT)
Hmmm...this is really hard to explain without talking in person (which we can do on Monday). But I think you misunderstood the definition of BW above. Bandwidth would be the bandwidth of the AC filter on the oscilloscope, I think. So, it's amazing the correlation you get with your measurements and that formula and I can't quite explain it. The shape of the signal on the scope should not change with frequency of input wave. Thus, the intrinsic tau for that curve should not change. So, there is something about the way you were measuring that produced the correlation with the formula.