User:Jacob R Jaramillo/Notebook/O Scope Lab

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O scope lab

SJK 01:19, 17 September 2009 (EDT)
01:19, 17 September 2009 (EDT)
Excellent job noting the exact model numbers, and also excellent job including the photos! It would be very easy for someone to replicate your setup based on this information--kudos!

Equipment:

Tektronix TDS 1002 O Scope

BK Precision 4017A PS

BNC cable

Getting Started:

Lab Assignment:

[[1]]

First I connected one end of the BNC cable to the Power Supply (PS) via the Output adapter and the other end of the BNC cable was connected to CH1 on the O Scope.

Ps.jpg

Oscope.jpg

Basic Measurements:

Once the BNC cable is connected and all devices are one, press the "Measure" button on the O Scope. The O Scope will disply Rise Time, Max V, Pk-Pk V, Fall Time and Mean values. Measurements are also made easy by utilizing the grid lines, the grid value is located at the bottom left hand side of the O Scope screen (this value can be adjusted with the VOLTS/DIV knob). To assist in centering the wave function, you can use the "Position" knob to move the wave vertically.

Triggering:

Triggering is used to display a "snap shot" of a waveform that does not have a high level of inconsistency, which is helpful in anaylyzing the waveform and making manual measurements. There are several ways to measure triggering, such as:

Type: Edge

1: Rising: Which picks a point (or allows you to manually select a point) near the end of the wave at a rising point and acts as a reset point.

2: Falling: Which picks a point (or allows you to manually select a point) near the end of the wave at a falling point and acts as a reset point.

SJK 01:27, 17 September 2009 (EDT)
01:27, 17 September 2009 (EDT)
For "video" and "pulse" I think you describe what happened for your signal, but this is not general. "Video" is good for video signals (such as NTSC) which have repeatable sync features. "Pulse" I am still not quite sure on, but if you do speed of light, we can investigate whether it's a helpful triggering mechanism (selecting based on pulse widths) for that lab.

Type: Video

Appears to display a reel of all voltage and frequency values, thus resulting in a rapidly fluctuating graph.

Type: Pulse

Appears to display a single "snap shot" of a waveform.


AC Coupling:

Capacitive coupling also know as AC Coupling is a process of placing a capacitor in series with the signal to be coupled often times to insure protection of the system. This capacitor is used as means of protection in case an output is shorted to ground or a supply voltage.

  • Interesting note, the O Scope defines fall time as "The time between 90% and 10% of the first falling edge of the waveform" and of course the exact opposite for Rise time.

Failed measurement: Even when using cursors to measure my voltage and calculating my 90% and 10% point, then switching back to measuring time with the cursor, my fall time didn't match the measured fall time calculated by the O scope under the "Measure" button. My fall time was measured to be 54.00ms and the O Scope measured 83.51ms.

SJK 01:18, 17 September 2009 (EDT)
01:18, 17 September 2009 (EDT)
These photos are great! However, even though I know what they mean, another reader is not going to understand them, because they do not have captions or any other description to say what the image is showing. Please do keep including photos! But also take the time to include a caption describing the photo.

Oscopeselfmeasurement.jpg Oscopemeasurement.jpg


RC constant: Resistance and Capacitance.

Summary

SJK 01:31, 17 September 2009 (EDT)
01:31, 17 September 2009 (EDT)
You're right that I'd prefer your pages to be in different locations. We can talk about this next week, and you should have plenty of time to learn how to do it. Briefly: I'd like the summary to be a separate page from the primary notebook. Also, having separate pages for each day, or at least each lab, in your primary lab notebook is good.

As mentioned above my self measurement for fall time using AC coupling was 54.0ms, which was obtained by calculating my 90% and 10% voltage points (vertical cursors) and referencing these points with the time scale (horizontal cursors) to come up with a exact number.

As in any measurement there are uncertainties, in this experiment I would say the largest would be the calibration of the O Scope as the O Scope probably has a +/- X.X ms tolerance. SJK 01:29, 17 September 2009 (EDT)
01:29, 17 September 2009 (EDT)
x.x??? Well, for sure in your next lab, you'll know some more about how to report uncertainty with more statistical rigor. E.g. "mean +/- standard error of the mean."

This lab definitely refreshed my memory of using an O Scope as it had been several years since I had used one. Of course anytime you don't use an instrument for over 5 years there are quite a few cob webs to brush out; however, this lab was very informative and helpful.

I found the following link "To AC Couple or Not to AC Couple? That is the question" which proved to be an interesting source relating actual applications/measurements.

[2]SJK 01:16, 17 September 2009 (EDT)
01:16, 17 September 2009 (EDT)
Cool link!
To tell you the truth I am still fairly confused as to why my self measurement and the O Scope measurement of fall time was so far off. I looked in the O Scope manual to verify that the O Scope calculation was using the 90% and 10% points as I had also used in my self measurement. I understand that ~30ms is an extremely small value; however, this should be well within the O Scopes capabilities???? SJK 01:09, 17 September 2009 (EDT)
01:09, 17 September 2009 (EDT)
I think your cursor measurements are correct and the o-scope is wrong! This is a great example of a talent of a good experimentalist: always questioning the instrumentation. As many other students found, the fall time measurement of the scope is highly dependent on what parts of the waveform you "show" the scope. Whereas, with the cursors, you as the informed user are able to better dictate what you actually want to measure. So, your 54 millisecond number is much more reliable, as you suspected.

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