Physics307L F09:People/Martin/Notebook/070829
Oscilloscope Lab
Getting Started
see comment
Upon walking in to the class my oscilloscope appeared to be set up already. Indeed this was the case. Turning on my oscilloscope gave me an instant sine wave, no messing around necessary. My wave function generator is a Wave Tech model 180 and a digital oscilloscope TDS 1002 (Tektronix)
Measuring my Wave
1) Count the lines- I can count this was easy, originally I thought that there was going to be some sort of numerical value associated with the dotted lines but as far as I can tell there is not. I count four lines from the trough of the wave to the peak of the wave. The oscilloscope made one period in about 3.5 vertical lines.
2) Using Cursors- It took me some time to figure out how to switch the cursors from a vertical line to a horizontal line, but as Dr. Koch pointed out it is like a ATM machine, meaning the side buttons have a function and switch between options. Using this method I found the distance between trough and peak to be 8.00 V, and that the frequency was 29.07 Hz. During this measurement I had to figure out which channel the cursors were measuring because the result from this section did not match the result from the next section, again ATM machine (easier then I thought).
3) Finally time to measure.- This tool was really neat. My final, hopefully correct, measurement was measured on the pk-pk option as 7.92 V. Using the freq option I found the frequency to be 28.7 Hz and using the Period function I found the period to be 34.8 ms.
see comment
Time to mess with the oscilloscope
Using small amplitudes is just mean, the waves start moving and it becomes difficult to look at the oscilloscope without becoming dizzy. Messing with the measuring function, while trying to retain my lunch, it seemed that the measuring function did not measure any inconsistencies in amplitude, there was a smooth enough transition through amplitudes to assume that the machine can measure small amplitudes. Even at higher amplitudes my oscilloscope seemed to be functioning properly and giving me a amplitude that made sense. Also the frequency does not change under the varying amplitudes, from very high to quite low. This is good a varying frequency reading would be a bad thing. Kyle + things moving around on a computer screen = bad. Changing the DC offset moves the sine curve around on the screen, see previous statement. For very high DC offset (I cannot see the graph any more it is off the screen) the measurement feature was way off to compare with my original case I got a pk-pk reading of 3.04 and then a question mark. Getting a "?" from any machine is not a good thing.
Triggering
Rising edge triggering-this is when the graph stops when the graph reaches an increase in voltage. There was a falling trigger option which is the opposite of the rising trigger option. There was also a video and a pulse trigger option. The video and pulse trigger options appeared similar in that they both had a wave that propagated across the screen slowly, messing with the voltage dial you can create a standing wave.
see comment
AC Coupling
2) For me it was easier to measure ripples in the edge trigger and in DC coupling. In the boxed wave form the ripples at the top of the boxes seemed to be easier to differentiate between then the ripples on the AC coupled graph.
3) Measuring fall time Setting my DC Voltage so that the pk-pk measurement was 6.08 volts, my eyed measurement with the cursor I found the fall time to be 48 ms. I then took the computer measurement and got 53 ms at a different amplitude I got 54.6 ms for a smaller amplitude and at a larger amplitude I got 52.8 ms.
4) The RC Constant The RC constant (resistance)(capacitance)=t which is proportional to the fall time, so in this case my RC constant was 53 ms.
5) Expected Value I found what looks to be the usars manual for the TDS 1002 users manual. Unfortunately I ran out of time to find the correct value for the RC constant but hopefully it is there.
