User:Arianna Pregenzer-Wenzler/Notebook/Junior Lab/2008/09/10

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Setting Up
Make sure oscilloscope is grounded (pluged into a 3-prong outlet),attach BNC cabel to chanel 1(oscilloscope)/output(function generator), set wave type on function generator (look at pictures over buttons), find your sine wave. Do this by either hitting auto set button or adjusting the screen width/height by using Volts/Div or Sec/Div knobs. Use a T connector and a terminator between the BNC cable and the scope if you are getting interference (a 'ghost' image) at high fequencies. Note; when trying to adjust your picture Sec/Div allows you to set time between horizontal intervals. Match that time to the inverse of the frequency(the period).

Dr Koch explained to me that if you have a signal with very high frequencies it can cause interference if it travels directly from the BNC cabel into the osciloscope, but if you use a T connector ending in a terminator the parts of the signal that cause interference travel down the BNC cabel and into the terminator, allowing for the scopes continued operation with out picture distortion. We also took some time to take a terminator apart and look up its resistance in wiki, using its color code(see lab summary).

Measuring Sine Wave
by grid: Adjust screen so that important points line up well to grid intersections, and aproximate by eye (each grid line is a division, each division is divided into 5ths):  Period=100ns, Amplitude=10V by cursor: Hit cursor botton chose horizontal or veritical measurments by slecting under type: Period=100ns,Amplitude=10V. by measure button:measure button, slect source, slect type, you are given a measurment: Period=100.6ns, Amplitude=10v. I need to move on but in making a few quick changes I can't find a readily apparent problem with the scopes ability to measure.

Triggering
The signal that sends the trace across the screen does not occur constantly, rather it sends a signal, and then waits for some indicator (a trigger) to tell it to send the next trace.(edit 9/15) Hit trig menue, type edge means the scope is triggering when an edge of the wave passes a set point, slope pos/neg means it is triggering of an increasing/decreasing point on the wave. Look more at the Wiki on this to get a better understanding

AC coupling
Manual measurment of the fall time of a square wave (to get a square wave with a noticeable fall time select a low frequency range). Set top (horizontal cursor) to the max height of the wave, take 10% of the value of height max and set the bottom cursor equal to this value, read off delta to get the change in volts after the wave has decreased by 90% from its max height. Ex: cursor2=16.8V, cursor1=1.60V, delta=15.2V Now measure with vertical cursors to measure the time between V(max) and 90%V(max). *NOTE; adjust the horizontal position of the wave so that cursor1, which is at a reather undifined pt on the curve lines up with a refrence pt on the grid. cursor1=11.20ms, cursor2=66.40ms, delta=55.20ms (18.12Hz) So the fall time is the change in time (delta = 55.20ms) Using measure button Hit measure, Source=CH1,Type=Fall Time, Value is given as 55.91ms, but is fluxuating by about +/-.3
 * fall time


 * What RC constant does this imply? (See Wikipedia article on rise time)

Boleszek's osciloscope notebook entry
 * I wasn't so sure on how fall time realted to rise time, nor did I come out of this lab with a solid understanding of AC vs. DC coupling so I looked up Boleszek's notebook entry. I had talked to Boleszek proir to my Wednesday lab about his experience in the Monday lab secession and he told me he had enjoyed the lab and taken extra time to make sure he got a good understanding of the osciloscope so his notebook seemed like a good place to start looking for information I had missed. Boleszek has a great notebook entry for the osciliscope lab, and he also found an alternative source for information on the relation between fall time and the RC constant.

[| electromic formula/time constants] I added the previous entry on the evening of 9/14, then I class today I found a written note from lab last week on how to calculate Tao, and therefore the RC constant. It is the same equation listed in the wiki article, but in that article they refer to it as rise time and I thought there might be a difference. note since V(initial) is only 90% (not 100%) of the total amplitude, Vi=.9, Vf=.1(10% of total amplitude) Honestly I have no idea what this means nor did I understand the difference between AC and DC coupling, I did realize, just as I was writing out this equation, that had I taken good data, ie: if I had made measurments multiple times I would be unsure how to figure my error into my calculation. If I had taken multiple measurments I would probably just average the results, for the measure button should I do the same? Should I average in my observed fluxuations?? I think I know or can figure out the answers to these questions, and if not I have many people I can go to for answers; Dr. Koch and my classmates to start with. The big lesson here is I am going to have to be more careful, take better measurments, and make better notes, and if I don't have a plan going into lab the first thing I need to do once I know what I'm doing is formulate one. I spent 3 hours Wednesday but I didn't know where I was going and so I mostly stayed put, in the future I think I can get alot out of lab but I'm going to have to be willing to try doing things I've never done before and might not be good at. I find its so much easier to do stuff I already have know how to do, but then I guess I don't learn much if I always play it safe.*Arianna Pregenzer-Wenzler 23:30, 15 September 2008 (EDT):
 * V(initial)=V(final)*exp(-t/Tao)
 * Vi/Vf = exp(-t/Tao)...ln(Vi/Vf) = -t/Tao...Tao = -t/ln(Vi/Vf)= RC constant
 * RC = Tao =(aproximately) -55.91ms/ln(9) = -25.45ms

To end  I will have to re-visit this information at home, I just need to shut everything down properly.*Arianna Pregenzer-Wenzler 19:08, 10 September 2008 (EDT):


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