User:Tyler Wynkoop/Tyler's Page/Oscilloscope

Oscilloscope Lab Summary

When first introduced to the Oscilloscope, most of the lab group (myself included) had very little understanding of what an Oscilloscope actually does, other than make sinusoidal waves on a screen. The lab's goals, naturally, were to enlighten fledgling physicists on an oscilloscope's functionality and utility.

Functions Studied Specifically

• Base Functionality
  • In other words: "What does an oscilloscope do?" Entering the first lab, Professor Koch explained that an oscilloscope is a tool used to measure patterns in anything that can be converted into voltage. For example, wave patterns and background noise in an AC voltage source.
• Settings and Controls
  • Setting up the oscilloscope's viewing window to appropriately view voltage patterns. This was accomplished by using the various dials an menus on the oscilloscope. One dial adjusted the vertical height of the voltage displayed, while others adjusted the time interval displayed. Learning to use the function generator was also necessary. The function generator was a voltage source from which we could adjust the voltage pattern to our liking. Dials on the function generator controlled the shape of the wave, amplitude, and frequency.
• Measuring Waveforms
  • The function generator generates time-dependent functions, as explained before. We used the oscilloscope's various measuring tools to determine various properties of the wave form.
  • Measurements taken
    • Using the grid lines on the Osc
      • Amplitude approx. 3.61V
      • Period approx. 2.00ms
    • Using cursors
      • Amplitude 3.64V
      • Period 2.000ms
    • Using the measure function
      • Amplitude 3.68V
      • Period 2.000±.004ms
• Triggering
  • Triggering is essentially the point on the wave when the oscilloscope begins to measure the wave form. I noticed that if the triggering position became larger than the amplitude of the wave, then the oscilloscope would display only segments of the wave form, overlapped in rapid succession, an undesirable result.
• AC/DC coupling
  • AC/DC coupling are two modes of the oscilloscope designed to either filter out (AC coupling) or allow (DC coupling) DC voltage when the oscilloscope displays a waveform and takes measurements.
• Fall Time
  • In the circuit that AC couples the oscilloscope, there is a capacitor which allows the DC voltage to be filtered. Fall time is the characteristic time for that capacitor to discharge. According to the formula: [math]\displaystyle{ V_0 = V_{max}*e^{-t/\tau} }[/math] Where (τ) is the fall time, a characteristic constant of the capacitor.
  • I experimentally found the fall time of the capacitor by adjusting the function generator to produce a square wave at very low frequency to allow the capacitor to discharge as much as possible, and measuring physically on the wave (cursors) and with the measurement function on the oscilloscope.
    • With cursors, the estimated value is 53.00 ms
    • With the measure function, the value is 55.6±.3ms^{SJK 14:33, 24 September 2010 (EDT)}

      

      14:33, 24 September 2010 (EDT)
      Great that you include estimate of uncertainty! It's unlikely in this case that the confidence interval is well-defined (as it would be if reporting standard error of the mean), but a great start! If there were an accepted value (as with most of other labs), a comparison to accepted value is essential as well, e.g., the electron charge in Millikan

Extraneous Experimentation

^{SJK 14:35, 24 September 2010 (EDT)}

14:35, 24 September 2010 (EDT)
I loved the extra studies you did for this lab. I love that kind of exploration in any of the labs, so keep it up!

• To understand the use of the oscilloscope more fully, after discussion Professor Koch suggested viewing the AC current straight from the building. Since the voltage from the wall socket was too intense for the oscilloscope to handle, he used a step-down to lower the voltage to within tolerable limits of the scope. I continued to refine the view of the oscilloscope to zoom in on several specific distortions in the wave. These distortions were apparently simply background noise, possibly from other electric devices in the room.

• I also found that the human body (my own in particular) emits voltage "noise." I discovered this by grounding one end of the test plug and holding the other in my hand. The voltage across this (my hand to ground) was enough to make the oscilloscope respond.
• After studying the voltage from myself, I returned to the wall socket in an attempt to analyze the background noise. My goal was to filter the regular AC current coming through to only get the noise. I attempted to filter this by setting my function generator to emit the same voltage and frequency of the stepped-down wall voltage, simply offset in phase by half a cycle. I then summed the waves via an oscilloscope function, attempting to cancel out the wall signal, leaving only the background noise behind.

Links

User:Tyler_Wynkoop/Notebook/Junior_Lab/Week_1

Physics307L:Labs/Oscilloscope