Physics307L:People/Josey/Oscilloscope
Oscilloscope Lab Summary
SJK 21:52, 21 September 2010 (EDT)
Hey Brian, This is a very good lab summary. It's the right scope of what I'm looking for in the informal summaries. I like that you give credit to Kirstin and you link to your primary notebook as well. The main thing missing from this page is a quantitative uncertainty on your measurements. That is, the "+/-" that we discussed in lecture on Monday. Every future lab will require this quantitative estimate of uncertainty and a discussion of the sources of uncertainty and whether your measurements are consistent with accepted values. On this page, you do discuss uncertainty a bit, which is good. I'll put more comments on your primary page.
For this lab, my partner, Kirstin, and I worked with a Tektronix TDS 1002 Oscilloscope, and a BK Precision 4017A Function Generator to understand the basic use and operation of an oscilloscope. The crux of the experiment, however, was to determine the fall time of an RC circuit by using AC coupling on a low frequency square wave. AC coupling is a process in which the oscillator will remove the DC portion of an input signal leaving only the AC portion. However, at very low frequencies, there is a waviness to the signals that represents the inherited physical properties of the RC circuit that is used to remove this portion. On a square wave, this waviness can be used to find the fall time of the circuit. The exact nuts and bolts of this procedure are given in my notebook page for it, here.
Results
For our generated signal, we created a square wave with a frequency of 11 Hz, and a max voltage of 8.56 V. This voltage was determined by the measure function before AC coupling was applied. We measured the fall time in two different ways, using the measure function and the cursors. The value for the measure function was given by the oscilloscope, while the cursor value was found by measuring the time and voltage of the signal at two points and plugging them into this formula:
[math]\displaystyle{ V_2 = V_1 e^ { \frac {-\Delta t} {\tau}} \, }[/math]
where τ is the fall time, giving us these values:
- Measure Function: 37.1 ms
- Cursors: 23.82 ms
Unfortunately, the cursor approach to measuring the fall time is greatly inaccurately as it relies on my ability to find a position on the graph by hand. Because of this, the cursors value is only 64% of the value given by the oscilloscope suggesting that there is a great discrepancy in the processes. More data points for different waves are needed to find a better estimate for the fall time.
Conclusions
This lab was a good introduction into the class, and I was able to learn a lot about the use of the oscilloscope, and function generator. I was also able to use the collect data on different waves and the fall time on the oscilloscope, and gain a refresher in electronics.
