Physics307L F07:People/DePaula/Notebook/070829

Oscilloscope Lab

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Steven J. Koch 02:05, 5 September 2007 (EDT):This lab notebook is a veritable page-turner! Seriously, very well done, all of the relevant information seems recorded and in your own style too. You do a great job of giving props to people and sources of information. Also seems clear that you learned a lot from this lab.

Set Up

I begin with a function generator, oscilloscope, and 2 BNC cables. With these tools I was ready to begin my descent into the world of the oscilloscope. I started by plugging in the function generator, and oscilloscope to the wall socket. Next I connected the output of my function generator (FG from here on out) to my Oscilloscope. After turning on both machines, and selecting English as my preferred language, although doing the entire lab in Spanish sounded intriguing, I noticed a whole lot of nothing happening on the oscilloscope display. I started messing around with knobs and still had no understanding on how to operate this mysterious machine, so I decided to read the 'directions' and labels.

Basic Waveform Measurement

For my first test frequency I chose 100 Hz because it looked quite clean and highly measurable on the display. I set the Variable knob at maximum. Professor Koch helped me obtain this test frequency by explaining to me what each label on both the FG and Oscilloscope meant in layman's terms. By messing with the Volts/Div knob, I settled on a scale of 500mV per grid unit. Using the triggering mechanism I focused the trigger on the rising edge of Channel 1, and adjusted the Volts/Div knob until the wave occupied most of the display. I did this to obtain a higher level of accuracy. The amplitude of my first test frequency measured by comparison to the grid underneath, was 1400mV. Next I learned from Professor Koch how to manipulate the cursors to give me a detailed measurement of both amplitude (Voltage) and Time. Using this method I recorded a value of 1.31V (1310mV) for amplitude. The final function I must attempt to understand is the "measure" menu. Upon opening the menu I see quite a few numbers and labels I do not recognize. After much thought and comparison I found that the Pk-Pk value for CH1 was exactly what I should be looking at, it displayed a value of 1.32V (1320mV) which is much more accurate than what I obtained using the previous two methods.

Test Frequency 2 (20 Hz) For my second test frequency I decided to use a value much smaller than my previous value of 100 Hz, and adjusted the amplitude to 1/2 that of the previous test wave. I obtained a value of 500mV by direct measurement, 424mV by cursor usage, and 424mV by internal Pk-Pk value.

Triggering

The basic purpose of triggering, is to put the oscilloscope in the time/voltage frame of the wave itself to help aid in measurements and comprehension of the wave itself. We will mostly be using edge triggering in this lab. Edge triggering searches the wave for the voltage pre-determined by the oscilloscope operator, and generates a pulse when that voltage is reached. A rising edge trigger is quite self explanitory, the trigger voltage is located on the rising edge of the wave, predetermined by the oscilloscope operator. The other types of triggering are as follows: Falling Edge: Same as rising edge but happens on falling edge instead of rising edge. External Trigger: Some other source provides a signal at regular or irregular intervals cuing the oscilloscope to generate a pulse. Video Trigger: A system extracts synchronized pulses from the oscilloscope and triggers a 'timebase' (thank you wikipedia) on selected intervals. Delayed Trigger: Uses an edge trigger, but waits a specified amount of time after edge trigger to generate pulse. This allows the operator to examine specific pulses.

AC Coupling

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Steven J. Koch 02:09, 5 September 2007 (EDT):It is great that you recorded the three measurements...this would help you in estimating the error in your measurement. Your values seem a little "all over the place" compared to others...not sure why this is, but we could probably figure it out if were were to investigate it.

I adjusted the FG to have a square wave with amplitude 8.6V. My FG does not have a DC offset. To measure the fall time using cursors, i found first what the value difference was between maximum and minimum,then calculated 10% of that value, and subtracted it from the total value. This will give me the exact delta I need to place the cursors as accurately as possible. The delta I calculated is 10V, so placing my bottom cursor 10V from the peak should give me an accurate fall time. This process yielded a value of 30ms for the fall time. Using the measure function, I found the fall time to be 33.68ms (average). Fall Time Measurement 2 I used a frequency of 15Hz to calculate the fall time a second time and found it to be 59.00ms Fall Time Measurement 3 I used a frequency of 25 Hz to obtain the fall time again, and calculated it to be 21.36ms The RC=t function just states that the resistance*Capacitance should be equal to my fall time, which I observed to be 33.68ms.