# Physics307L F09:People/Muehlmeyer/Oscilloscope

Purpose

SJK 14:32, 17 September 2008 (EDT)
14:32, 17 September 2008 (EDT)
This is a very good lab summary, except for the missing uncertainty on the "final values" (which is a big deal for future summaries). It reads well and is a good summary of what you did and links to your primary lab notes.

The digital oscilloscope is a necessary tool in every lab, and as young students of physics, it is very important that we begin understanding this tool not only for use in future labs, but also as a matter of giving our theoretical knowledge of physics the tools necessary to apply such knowledge.

This lab is a practice lab. We will learn our experimental procedure when it comes to safety, online data recording and note taking, and lab summaries.

In the experiment itself we will leanr basic functions of the oscilloscope: triggering, measuring with cursors, measuring with the digital functions, AC Coupling and we will use this data to calculate the fall time of an AC coupling.

The Procedure

I will omit the nuts and bolts of how I learned the basics of oscilloscope use. Those notes can be found in my lab notes

AC Coupling

Capacitive coupling allows us to filter out an AC or DC signal so that we can observe the other. In AC coupling we filter out the DC component. I actually split the signal and put it into two seperate channels to observe the difference between AC And DC signals. In my notes I observed that "Channel 1 gave me a very high resolution plot of the AC "ripple" that permeates the DC signal. This AC ripple is the noise in the DC channel. Channel 2 on the other hand shows me the DC current to a much less resolution, I cannot see the ripples to such an intense degree."

I successfully "coupled out" the AC signal from the DC signal.

Measuring the Fall Time

We took two approaches to measuring the fall time of our AC coupled square wave: 1) We used the cursors and measured by eye. 2) We used the fall time function on the oscilloscope.

Using the cursors is a bit in accurate, especially since one must estimate the point at which the decaying wave falls to 10% of its original value. Using the cursors I measured my fall time to be 39 ms.

SJK 14:29, 17 September 2008 (EDT)
14:29, 17 September 2008 (EDT)
I think in most cases, the cursor measurements were either in-line with the "measure" function, or were actually more reliable. So probably in your case there was some problem with your cursor method that we didn't notice at the time.

The fall time function on the oscilloscope measure the fall time of my wave to be 44 ms. My cursor measurement then was 89% of the "true value" measured by the oscillscope. Error: 11%

Data Summary:

• Fall time (cursor)=39 ms
• Fall Time (measure)=44 ms
SJK 14:31, 17 September 2008 (EDT)
14:31, 17 September 2008 (EDT)
In all of your lab summaries, you will need to present final results with uncertainty, which is missing from these two values. You do discuss "error" above, as the relative difference between the two values, but that is different than the uncertainty of each individual value. You'll be learning a lot about this in the coming weeks!

In Summary:

• I learned the basics of oscilloscope use.
• I learned to save my lab notebook often.
• I learned a bit more about the difference between AC and DC current.
• I obtained data for the fall time.
• I learned the experimental procedure we will use from this point on.

In the future:

I think this was a great introduction to Junior lab.