User:Jason O Archer/Notebook/PHYC 307L Junior Lab/2008/09/08

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Oscilloscope Lab 9/8/08
After turning on the oscilloscope and the function generator, I connected the 'LO' output of the function generator to the Channel 1 input of the oscilloscope using Bayonet Neill-Concelman (BNC) cables. (I attempted connecting the 'HI' output, but the resulting waveform on the oscilloscope was more difficult to read). As per Dr. Koch's website's suggestion, I set the frequency of the waveform to 200 Hz.

After receiveing some unusual readings on the oscilloscope (thick black lines indicated by the oscilloscope to be a waveform), I adjusted the 'SEC/DIV' (seconds per division) until a clear sine wave appeared on the order of 10 milliseconds per division. At this point, a display on the oscilloscope indicated that the waveform had been triggered.

From a preliminary examination of the waveform based on the division grid of the oscilloscope, I found that the peak-to-peak voltage of the waveform was roughly 500 ± 100 millivolts (mV), and the period of the waveform was roughly 5 ± 5 milliseconds (ms). From a second, more precise examination of the waveform using the cursor function of the oscilloscope, I found that the peak-to-peak voltage was 508 ± 16 mV, and the period was 5.2 ± 0.8 ms. Finnaly, using the pre-programmed measuring functions of the oscilloscope, I measured the peak-to-peak voltage to fluctuate between 504 and 508 mV, and the period to fluctuate between 5.128 and 5.144 ms.

I adjusted the function generator to produce a wave with very high amplitude. From a preliminary examination of this new waveform, I found the peak-to-peak voltage of the waveform to be roughly 2200 ± 200 mV, and the period of the waveform was roughly 5 ± 5 ms. From the second examination of the waveform using the cursor function, I found that the peak-to-peak voltage was 2.22 ± 0.08 V, and the period was 5.2 ± 0.8 ms. Finnaly, using the pre-programmed measuring functions of the oscilloscope, the peak-to-peak voltage fluctuated between 2.18 and 2.20 V, and the period fluctuated between 5.110 and 5.150 ms.

I adjusted the function generator to produce a wave with very low amplitude. This waveform had such a low amplitude that the oscilloscope lost its trigger and I had to adjust the 'VOLTS/DIV' voltage scaling to restore it. From the preliminary examination of this third waveform, I found the peak-to-peak voltage to be roughly 60 ± 20 mV, and the period of this waveform to be roughly 5 ± 5 ms. From the second examination of this waveform using cursors, I found the peak-to-peak voltage to be 59.2 ± 3.2 mV, and the period was 5.2 ± 0.8 ms. Finally, using the pre-programmed measuring functions of the oscilloscope, the peak-to-peak voltage fluctuated between 60.0 and 63.2 mV, and the period fluctuated between 5.100 and 5.170 ms.

I adjusted the function generator again to produce a wave with very large DC offset. This waveform had such a large DC offset that the oscilloscope lost its trigger a second time and I had to adjust the coupling to AC coupling to restore it. From the preliminary examination of this fourth waveform, I found the peak-to-peak voltage to be roughly 900 ± 100 mV, and the period of this waveform to be roughly 5 ± 5 ms. From the second examination of this waveform using cursors, I found the peak-to-peak voltage to be 880 ± 32 mV, and the period was 5.2 ± 0.8 ms. Finally, using the pre-programmed measuring functions, the peak-to-peak voltage fluctuated between 864 and 872 mV, and the period fluctuated between 5.130 and 5.140 ms.

Either the oscilloscope has some difficulty measuring low-frequency square waves and triangle waves, or the function generator has difficulty creating them.

Triggering on the rising edge means tracking a waveform from a point at which the waveform has a specific voltage which is rising relative to time.

Using a falling edge trigger shifts the stationary waveform left or right (relative to time), but does not move it. Pulse and video triggering move the waveform to the right (relative to time). No triggering methods shift the waveform up or down (relative to voltage).

After switching the output of the function generator from 'LO' to 'HI', I was able to generate a DC offset of 11.4 V. AC coupling was far more effective in reading minor fluctuations or "ripples" in the signal.

Adjusting the waveform to Dr. Koch's website's specifications of a square wave with no DC offset and an amplitude of roughly 8.6 V, I used the cursors to measure the fall time from the peak of the waveform to a value of 10% of that peak. This value was 54 ± 8 ms. Using the pre-programmed measuring function of the oscilloscope, I found a very different fall time fluctuating between 163.5 and 164.0 ms. This discrepancy appears to arise from the oscilloscope measuring fall time to the next trough of the function, not to 10% of the peak. The cursor measurement implies a time constant of (54 ± 8)/2.197 ms = 25 ± 3.6 ms.

Aram asked me to recreate the waveform. At this point I realized I had made an error of not recording the frequency of the waveform. He also instructed me that I should create the waveform with an endpoint close to zero, not to 10% of peak that I had done. I was able to generate a 1.4 Hz square wave with no DC offset and an amplitude of roughly 8.6 V. I used the cursors to measure the fall time from the peak of the waveform to a value of 10% of that peak. This value was 58 ± 4 ms. Using the pre-programmed measuring function of the oscilloscope, I found a similar fall time fluctuating between 49.40 and 56.00 ms. The cursor measurement implies a time constant of (58 ± 4)/2.197 ms = 26.3 ± 1.8 ms. The programmed measurement implies a time constant of (52.70 ± 3.30)/2.197 ms = 24.0 ± 1.5 ms. These values are close, so I can assume my cursor measurement was somewhat valid.


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