User:David K. O'Hara/Notebook/physics 307 lab/Oscilloscope lab summary

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Oscilloscope Lab Summary

SJK 16:42, 15 September 2009 (EDT)
16:42, 15 September 2009 (EDT)
I like this lab summary. Particularly the two sections "measuring values..." and "measuring fall time," where you do a good job of concisely reporting the values and discussing the uncertainty. Keeping this kind of summary in mind for your future labs will work well, I think. Importantly, make sure you have units on your measurements; make sure you link to your primary lab notebook. Also, you will need to implement rigorous uncertainty analysis (such as mean +/- standard error of the mean) in future labs.
SJK 16:36, 15 September 2009 (EDT)
16:36, 15 September 2009 (EDT)
Make sure to put a link to your primary lab notebook in the summary. Also any other links that the reader may want to see...for example, the oscilloscope lab page in this case.

Lab Objective
The purpose of this lab was to become familiar with oscilloscope operation and to become accustomed to using "wiki" as a document editor.


With all electrical equipment there are dangers to both people and equipment that require a certain amount of cautioun to used when working with energized electrical components. When moving energized electrical equipment you have to be careful of avoiding shocks by touching or otherwise creating an electrical short in the equipment. In fact all electrical equipment should be in place and properly setup before any of the items are energized. No open drinks or other unsafe behavior is acceptable while working with energized electrical equipment.

To protect the equipment that will be used, do not exceed voltage or amperage ratings.

Equipment Used
Tektronix tds1002 two channel oscilloscope
BK Precision 10MHz sweep/function generator

Lab Procedure
We completed multiple excersises with the goal of becoming familiar with oscilloscope controls.

Using a wave function generator we output a signal from that and ran it straight into the oscilloscope.
The basic function of Triggering is that it allows a stable representation of the waveform to be displayed on the scope.

First we used the Triggering functions to see what different triggering settings had on the wave display.

Effects of using different triggers:
video - shows continuously moving waveform, difficult to read. This setting is meant for a video input signal and used on the signal we were working with, it had no noticeable effect.
pulse - had no effect, display was similiar to video
edge - this setting gave a stable representation of the waveform, it generates a pulse when the intput signal crosses a given threshold voltage and with the correct timing settings we were able to set up a stable view of the waveform output by the function generator.

Measuring values off oscilloscope

using a 200hz sine wave signal from a function generator measure the peak-peak voltage (amplitude) and the period (giving frequency)

perform measurements using oscope display divisions, cursors, and finally measure function.
measurement type voltage period frequency
display 2.3 v 4.8 ms 205 hz
cursor 2.24 v 4.84 ms 206.4 hz
measure 2.24 v 4.840 ms 206.446 hz

As it is quite evident from the data taken in the table the three modes of measurements were quite different in the amount of precision that was able to be used for each measurement. When simply trying to read the values from the display it was difficult to obtain anything closer than a ballpark estimate of the values being read. When using the cursors to pull the values off the display the precision improved but the accuracy of the reading was still subject to how the cursor was set up and how the operator placed the cursor on the oscilloscope. The final method of obtaining voltage and period values was to simply let the scope pull its own values. Obviously this was the most accurate of the three types of measurements and the easiest to obtain.

compare AC coupling to DC coupling

AC coupling shows entire wave makeup, both AC and DC parts.

DC coupling shows waveform with only DC component. Filtered waveform.

measuring fall time. Using the scope to measure the fall time on a very low frequency signal (~1hz). Set the function generator to output a square wave with 0 dc offset, and an amplitude of 8.6 volts @1.1hz. After setting up the scope to display one single instance of the given waveform, using the cursor settings to obtain the fall time of the given signal where the voltage amplitude has fallen from its peak value to 10% of that value. Using the fall time measured, it is possible to calculate the RC constant of the oscilloscope using the formula of fall time = 2.197*τ where τ=RC.

I measured the fall time from the peak of the signal to 10% of the signal to be 53.3 ms.

This in turn gave an RC constant of .024.SJK 16:39, 15 September 2009 (EDT)
16:39, 15 September 2009 (EDT)
Make sure to always put units on numbers when presenting final results. In this case, we can figure out the units are seconds, since you gave the formula. But try to get in the habit. Also, it'd be better to keep the units as milliseconds, since that's how you reported the fall time.
Using the cursors to make the measurement off the display does put in doubt the precision of the value given by calculating τ based on neasurements made by eyeballing the 90% drop off of the peak to peak voltage of the oscope display. The precision of the measurement could be improved by taking multiple readings and averaging them, but the inherent systemic imprecision of human control of the cursor setup will still leave a fair amount of error even in the case of multiple statistical runs.