# User:Anastasia A. Ierides/Notebook/Physics 307L/2009/08/24

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## Oscilloscope Lab

SJK 22:22, 14 September 2009 (EDT)
22:22, 14 September 2009 (EDT)
Excellent job on your lab notebook and summary! Other than the minor things I've written throughout, I really like what you did in both the primary notebook and the summary. I also liked how you and Alex had a lot of fun while trying hard and learning a lot during this lab. Good work!

Partner: Alex Andrego

### Set Up & Procedure

SJK 22:21, 14 September 2009 (EDT)
22:21, 14 September 2009 (EDT)
Excellent job on the methods here and especially putting down exact model numbers. Two things: (1) you should link to the procedure you're following (the oscilloscope lab page). I know you linked it on your summary and below, but it would be good to explicitly say here that you're following those instructions. (2) Photos would help! I know you may not have a good way of getting photos into your lab notebook. Maybe you could ask an iphone-blessed labmate to give you a hand?
1. Obtain oscilloscope (Tektronix TDS 1002), wave generator (BK Precision 4017A), and BNC cable
2. Connect the oscilloscope to the function generator with the BNC one end in the scope's Channel 1 port the other on the Lo Output of the function generator
3. Set the oscilloscope to display channel 1
4. Turn off the variable volts/division and all magnification settings
5. Set the channel 1 input coupling to DC, the trigger mode to auto, and the trigger source to channel 1
6. Set the intensity control to a nominal viewing level and adjust the focus control for a sharp display
7. Hook up the output of the function generator to the oscilloscope and set the output function to sine
8. Begin measurements using the grid, the cursor, and "measure"
9. Repeat the last step for different waves of various amplitudes and large DC offset

### Measuring The Sine Wave

1. Counting Lines. The amplitude of the wave generated is two lines above the equilibrium, about 1V. We used the Volts/Div knob to adjust the size of our graph.
2. Using The Cursor. Using the cursor we saw that it is 1.04V.
3. Using Measure. Using the measure button the max value for the amplitude was 1.04V as well.
4. Different Waves/Further Investigation:

When using different frequencies we arrived at different values for each trial summarized in the following table:

### Triggering

1. A rising edge is the positive slope of the signal wave pulsed into the oscilloscope by an external source.
2. Using different triggers:
• Pulse basically allows us to view an instantaneous, unaltered pulse
• Edge allows us to view the rising or falling edge of a pulse
• Video allows us to view the whole unaltered pulse of both rising and falling

### AC Coupling

According to the helpful sites mentioned on the Oscilloscope lab page, AC coupling allows only AC signals, blocking out DC signals using a capacitor and only the AC wave appears. DC coupling allows both AC and DC signals and the wave appears "sketchy".SJK 22:10, 14 September 2009 (EDT)
22:10, 14 September 2009 (EDT)
I don't think "sketchy" is probably the best way to describe it. DC coupling will faithfully represent the wave (except for very high frequency features), so there's not too much sketchy about it.
With our observations when switching to DC we were able to view wave patterns of very low frequencies (<10 Hz) whereas with AC we were only able to view the higher frequency wave (~79 Hz) while the lower frequency wave was not visible. Therefore we have concluded that the AC coupling mode is better for viewing the rippling on the DC voltage.
Measure the "Fall Time" for AC Coupling
Our directions for this part were to set the function generator to output a square wave with zero DC offset and an amplitude of about 8.6 V. We used the cursors to measure the fall time, peak to 10% value, and then used the "measure" function to measure the fall time of the square wave.
Using Cursors for 10% Value
We measured 50.4ms by using the cursor menu and choosing the time function. We used the position tuning knobs to find reference points on the grid by moving the screen area. Our 10% value was approximately 2.12V but because our instrument couldn't approximate that exact value we ended up using 2.20V as a reference.
Using the Measure Function
Using the "measure" function on the oscilloscope and choosing the "fall time" option, we measured 83.8 ms as our fall time. There is no certainty as to why this value is larger than the cursor value, but we have been experiencing this problem with our machine throughout this lab. There must be some sort of error with the measure function and therefore we do not trust the value given here.SJK 22:12, 14 September 2009 (EDT)
22:12, 14 September 2009 (EDT)
I like your lack of trust here and the fact that you discuss the discrepancy with your cursor measurement! I actually don't think the scope is broken, but rather it's just something about the "measure" feature that we don't understand. Very good that your experimentalist's instinct kicked in.
RC Constant
Using the fact that a capacitor charges at the same rate as it discharges, and according to the http://en.wikipedia.org/wiki/Rise_time article on rise time as well as http://www.kpsec.freeuk.com/capacit.htm, we find that the RC constant is RC<<T where T is the time signal implied by our results due to the resemblance of our screen of spiked charges and that of the circuits web page that we consulted.
The expected value of our fall time is given by:
$-t\div \ln (V_f/ V_i)\equiv \tau$
Where τ is the expected value, the ratio of Vf / Vi = 0.1, and t is our measured value. So, plugging these values into the above equation we get:
$\tau \simeq 21.9 ms$

### Oscilloscope Lab Summary

This is the link to my Oscilloscope Lab Summary: Oscilloscope Lab Summary

### Acknowledgments

SJK 22:18, 14 September 2009 (EDT)
22:18, 14 September 2009 (EDT)
Great job with the acknowledgments and links!

Of course my lab partner: Alex Andrego

And here are the websites that my lab partner and I found very useful: