Oscilloscope 101

This lab assignment gave us some insight on how to use an oscilloscope. First, we were given an explanation that the oscilloscope consists of a CRT electron gun that drives electrons towards a phosphor screen. When the oscilloscope is turned on, a white dot is visible at the center of the screen. The white dot is moved by electrostatic deflection by moving the deflection plates, which the user controls by adjusting certain time-based controls. We were also told that by default, the oscilloscope internally generates a sawtooth function.  We were also informed that the oscilloscope contains two input channels, which are the ALT and CHOP modes. Finally, we were shown the the TRIGGER input, which generates the waveform.

To begin Exercise 1, we were told to energize the function generator and the oscilloscope and to connect the function generator to Channel 1 of the oscilloscope. We made sure that the red banana jack was connected to the red banana jack and likewise for the black banana jacks. We then pushed the appropriate button on the function generator in order to produce a sinusoid and adjusted the frequency to 5 kHz. Then we set the peak-to peak amplitude to be 5 V. The screen read "enter number" so we went ahead and entered the value of 5 V. The word "offset" did not appear on the screen, so we did not have to worry about this part.  Next, we were to verify the scope by pressing the auto-scale button while turning off Channel 2. We then made sure to turn on Channel 1 and while pressing the "edge" button ans selecting "1". The "d" knob was adjusted so that two cycles of the sinusoid was visible on the screen. We then used the "e" knob to center the sinusoid. We then used the "c" knob to make the waveform as large as possible on the screen. The trigger level was adjusted so that we could check whether or not synchronization was lost or not. Finally, for the fun part, we measured the period to be 0.208 ms using the cursor button while toggling between X1 and X2. We then measured the peak-to-peak amplitude to be 5 V by also using the "cursor" button and toggling between Y1 and Y2. Using the basic concepts of a sinusoid graph, we computed the zero-to-peak amplitude to be 5/2 = 2.5 V. The formula Vrms = V/sqrt(2) = 2.5/sqrt(2) gave us the rms value for the anticipated voltage. To wrap up Exercise 1, we were instructed to make a verification of our results with the multimeter. We were to make both DC and rms AC voltage measurements. We made sure that the function generator was attached to the multimeter and left it this way for the rest of the experiment. The Vdc came out to be 62mV and the Vac came out to be 2.34 V. We noted that the Vac value of 2.34 was somewhat close to the oscilloscope's peak-to-peak value of 2.50.

We were then instructed to begin Exercise 2, in which we included a DC offset. We pressed the offset button in order to add a DC offset of 4.5 V. The screen was still properly displayed, so we didn't have to adjust any knobs for this part. Next we browsed the CH1 menu and selected button "a" to make sure that DC coupling option was selected. We were then asked to make a sketch of the waveform. Notice how the waveform is above the x-axis.

We then pressed the coupling button in order to switch to AC coupling mode. We then made some adjustments with the toggling buttons so that the waveform would then be properly displayed. We then made a sketch along with the V/div and s/div parameters. Notice how the AC coupling sketch is symmetrical along both axes, unlike in the DC coupling mode where the graph is shifted vertically.

To wrap up Exercise 2, we made some DC and AC voltage measurements with a multimeter. We obtained values of Vdc = 5.35 V and Vac = 2.45 V. These measurements justified the vertical shifting of the DC curve.

Now for Exercise 3, we were instructed to display and measure a square wave with an offset. We made the necessary adjustment on the function generator by pressing button 2. We were the told to measure DC and AC values using a multimeter. We obtained values of Vdc= 5.20 V and Vac 5.13 V. We were then instructed to change the scope to DC coupling and then to sketch the waveform along with the parameters.

Finally, for Exercise 4, we were asked to measure a mystery signals given to us by our instructor. First we disconnected the function generator from the scope and the multimeter. We then connected Channel 1 of the scope to the mystery signal panel. The photo below shows the values of the DC voltage, frequency used, and the peak-to-peak amplitude.

In my opinion, I believe that the lab assignment really helped to reinforce the concepts of sinusoidal waveforms of AC analysis to a deeper level. Even though we used oscilloscopes frequently in my physics classes, I never knew about the technical specifics of the oscilloscope until now.