User:Alexandra S. Andrego/Notebook/Physics 307L/2009/08/24

Oscilloscope Lab

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Materials

^{SJK 22:39, 14 September 2009 (EDT)}

22:39, 14 September 2009 (EDT)
good that you have this section...exact model numbers here is very important! Also, a picture would really help. You may not have a phone which can do so, but you could ask a lab-mate (or me) to help out.

Wave generator
oscilloscope
BCN cable

Set Up

To see the Lab guidelines visit the oscilloscope lab wiki page ^{SJK 22:42, 14 September 2009 (EDT)}

22:42, 14 September 2009 (EDT)
Very important to include this link, good job.

To begin the experiment the following preliminary steps were taken

Obtaining and plugging in the oscilloscope and the wave generator
Setting the generator and oscilloscope to their standard settings and functions.
Including the following list of standard procedure as described in the Oscilloscope tutorial:
- Setting the oscilloscope to display channel 1
- Setting the volts/division scale to a mid-range position
- Turning off the variable volts/division
- Turning off all magnification settings
- Setting the channel 1 input coupling to DC
- Setting the trigger mode to auto
- Setting the trigger source to channel 1
Using a BCN cable to connect the output connection of the generator with the channel 1 connection of the oscilloscope
Using the output level and trigger knobs we adjusted the sin wave on the screen until it was a standing wave and clearly visible

Measurments of the Sine Wave

First: Using Grid Lines

The sine wave's amplitude can be measured using the gridlines on the screen of the oscilloscope. Our sine wave is aproximatley two grid lines high which results in about 1 volt.

Second: Using Cursors

By using the cursor function on the oscilloscope we are able to find that the amplitude is more accuratley measured to be 1.04 volts.

Third: Using Measure Functions

By using the measure function on the oscilloscope we are able to find that the amplitude is similarly measured to be 1.04 volts like the cursor function found.

Further Investigation

When we take a look at different freqency of the sine waves and the measurment of their amplitudes we were able to see a significant difference in the measurments of the amplitudes. When the Frequency was increased, the amplitude did not increase or decrease in direct corrolation. When we gave the sine wave a large DC Offset we were able to see a very large amplitude for a medium sized frequency.

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When we increased our voltage above 12 V the generator was not able to compute the sine wave, and instead gave us a "topped-out" or "flatlined" function.

Triggering

What is a "Rising Edge"?

A rising edge refers to the positive slope of the signal wave seen on the oscilloscope.

What does the Trigger do to the Signal?

^{SJK 22:41, 14 September 2009 (EDT)}

22:41, 14 September 2009 (EDT)
Good job with the rising/falling edge triggering. I think you learned the concept overall, but want to point out that "pulse" and "video" triggering are specialized functions that you won't typically use, unless you're anlayzing video signals or certain kinds of pulses.

Video triggering allows us to view the entire signal unaltered or frozen.
Pulse triggering allows us to see the unaltered and instantanious "pulses" of the full signal.
Edge triggering allows us to view a particular part of our signal function
- Rising edge lets us view and stop the positive slopes of our signals at the times they are rising.
- Falling edge displays a halted image of the negative slope of our signal at the times they are falling.

AC Coupling

AC coupling removes the DC current where DC coupling takes into account both forms of current but filters out very small frequencies.

Which mode (AC or DC Coupling) is better for viewing a "ripple" on the DC voltage?

The AC Coupling setting makes it easier to view the "ripples" in the DC voltage because the DC Coupling setting shifts the signal to a much higher voltage and hence out of visual range on the Oscilloscope screen. The AC setting allows us to focus the screen more easily to the signal and hence the ripples are more easily seen.

Measure the "Fall Time" for AC Coupling

Function generator

Square wave

zero DC offset

amplitude about 8.6 V

Using Cursors: 10% Value

We measured 50.4ms by using the time function in the cursor menu. We were able to use reference points on our grid by moving our screen area with the position tuning knobs. our 10% value was 2.12V but because of the instruments we were only able to use 2.20V as a reference.

Using the Measure Function

We measured 83.8 ms by using the falltime option in the type category of the Measure function on the oscilloscope. We are not sure as to why this value is much larger than the cursor value gave us.

We have been seeing this error in the measure function throughout this lab.

Hence we do not trust this value ^{SJK 22:44, 14 September 2009 (EDT)}

22:44, 14 September 2009 (EDT)
This is good experimentalist's instinct: trusting the measurement you understood (cursors) much more than the one that you don't understand and which doesn't seem to be working. Keep trusting that instinct!

What RC Constant is Implied?

The RC constant RC<<T Where T is our time constant is implied by our results because the signal resembled spiked changes like described in the circuits web page that we consulted.

Comparison with the Expected Value

The expected value for the fall time of an oscilloscope can be found using the equation -t/[ln(Vf/Vi)]=Tau where Tau is our expected value. So we can plug in values to get our expected outcome.

-52ms/ln(.1)= Tau = 22.58ms

^{SJK 22:47, 14 September 2009 (EDT)}

Summary

If you wish to see my informal summary of this lab follow this link

Acknowledgements

^{SJK 22:49, 14 September 2009 (EDT)}

Oscilloscope tutorial
Triggers on Hobby.com
Tom Mahony's Lab Book
Paul Klimov's Lab Book
Physics 307L Oscilloscope Lab
Wikipedia Article on the Oscilloscope
AC/DC Coupling Info from Zone.ni.com
Circuit Info from Kpsec.freeuk.com