User:Chad A McCoy/Notebook/Jr. Lab/2008/09/08

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Jr. Lab #0: Oscilloscope Main project page
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Oscilloscope Lab: 9/8/2008

SJK 02:27, 17 September 2008 (EDT)
02:27, 17 September 2008 (EDT)Very good lab notebook.  I would say the major thing missing is the description of ALL the equipment and the connections that were made.  Also, sometimes the settings of the function generator were not specified, though usually they were.  Except for those omissions, very good work.
02:27, 17 September 2008 (EDT)
Very good lab notebook. I would say the major thing missing is the description of ALL the equipment and the connections that were made. Also, sometimes the settings of the function generator were not specified, though usually they were. Except for those omissions, very good work.

Basic use

  • For our lab, we are using a Tektronix TDS1002 Two Channel Digital Storage Oscilloscope SJK 02:20, 17 September 2008 (EDT)
    02:20, 17 September 2008 (EDT)Great that you record this model number!However, I don't see the model number for function generator, and so far not details of connections.  You will want to spend more time on this in future labs, so you know all the equipment that was used.  Pictures are great too.  (Imagine a student next year trying to replicate your experiments by reading your lab notebook.  Give them all the information they would need.)
    02:20, 17 September 2008 (EDT)
    Great that you record this model number!

    However, I don't see the model number for function generator, and so far not details of connections. You will want to spend more time on this in future labs, so you know all the equipment that was used. Pictures are great too. (Imagine a student next year trying to replicate your experiments by reading your lab notebook. Give them all the information they would need.)
  • The oscilloscope originally was set to give the data set as a series of dots, thereby making it impossible to see the defined sine wave as with the dot print style the graphs showed up as individual points without connecting lines to show the graph of the function. When Professor Koch came over he helped me determine that I needed to change the print function to vectors so that I would see the actual graph of the sine curve.
  • After setting the dividers to 5 volts vertically and 1 millisecond horizontally, the display showed 2 full periods of oscillation.
  • By inspection, the sine wave had a period of approximately 5 milliseconds and total amplitude of 22 volts.
  • Using the cursors, the frequency came out to be 200 hertz, plus/minus 1.6 Hz, and the amplitude measured to be 22.2 volts plus/minus .2 volts.
  • With the measure functions in the oscilloscope, the frequency was measured to be 199.8 Hz, with amplitude of 22.2 volts.

Triggering

  • Using the different trigger functions appeared to have different results in the on-screen appearance, as the rising and falling slope functions showed inverted graphs of the same function width, whereas using a pulse trigger differed based on the type of trigger pulse, be it equal time, greater than the time, or less than the time. The display also differed as the pulse time was altered, as it measured the time of the pulse having positive voltage, such that for a function with mean voltage approximately zero, the apparent graphs would center on each other for the successive triggering if it was set for equal time with the pulse length approximately half the period of the wave.
  • Using the triggering, Professor Koch, Aram, and I were able to determine that the pulse setting measured the time with voltage greater than zero by adding a positive DC offset to the curve from the generator such that the voltage was greater than zero for a longer period of time.
  • Using a square wave, I noticed that the fall between the high and low measured values had a dip of approximately 650 mV below the rest value, along with a time for the voltage to change approximately 70 ns, regardless of the frequency and amplitude of the function output by the generator.SJK 02:24, 17 September 2008 (EDT)
    02:24, 17 September 2008 (EDT)I'm not sure exactly what you mean here.  Is this the rounding off of the square wave?  Probably due to the upper bandwidth limit of the o-scope or the function generator...more likely the function generator..
    02:24, 17 September 2008 (EDT)
    I'm not sure exactly what you mean here. Is this the rounding off of the square wave? Probably due to the upper bandwidth limit of the o-scope or the function generator...more likely the function generator..
  • The last thing that was determined was that the mean function in the measure tools displays the mean of all points visible on the display at a given point in time, such that if the display is centered on values with voltages significantly different than the mean for the full data, the mean that is displayed is that of the currently shown values. This was determined by Prof. Koch, after the question was proposed by Aram, as he narrowed the window and centered it on the peak values of the data and we noticed the mean changing as the window was altered.SJK 02:25, 17 September 2008 (EDT)
    02:25, 17 September 2008 (EDT)I do remember that we came to this conclusion, but that still seems pretty weird to me...so I still don't quite believe it!
    02:25, 17 September 2008 (EDT)
    I do remember that we came to this conclusion, but that still seems pretty weird to me...so I still don't quite believe it!

AC vs. DC coupling

  • With a large voltage applied on the input of the oscilloscope, the DC coupling showed a smooth square curve, whereas the AC coupling showed a exponential decline in the voltage from the peak at a value of positive 22.6 volts.
  • To measure the fall time of the capacitor in the oscilloscope, I ran a single acquire sequence with amplitude 45.2 volts and frequency 79.3 mHz. In doing so, the fall time as given by the oscilloscope was 52.60 ms, and that given by the cursors was 53 ms plus/minus 2ms.
  • Therefore, to measure the time constant, we use the formula V = V0 * (1 − e(t / tau)) and when substituting V=.1, V0=1, and t=.0526, we get .1 = e(0.0526 / tau), and solving for tau gives tau = − 0.0526 / ln(.1), therefore tau = 0.0228s


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