Experiment 6

The Oscilloscope and the Function Generator

The oscilloscope and the function generator are essential equipment in any electronics laboratory. The Agilent DSO 1002A series oscilloscope is a digital device, which can be connected to a computer. The laboratory station computer communicates with the oscilloscope. using Run Imuilink Data Capture software. Digitized oscilloscope images and image data can be transferred to the computer using that software. Similarly, image information can he stored within the oscilloscope itself. The HP 33120A function generator is also a digital device, which is connected to the laboratory station computer.

Before starting this experiment, it is necessary to configure the output impedance of the function generator:

1. Push the Shift key, and then push the Enter key. The message "A MOD MENU' is displayed.
2. Push the ">" key three times. The message "D: SYS MENU" is displayed.
3. Push the "v" key twice. The message "50" is displayed.
4. Push the '>" key to change "50" to read "HIGH Z". This is the setting needed Ibr the experiment.
5. Push the Enter key to complete the set up process.

Part 1

1. Use the Freq key on the function generator to set the frequency to 100 Hz.
2. Use the Ampl key on the function generator to set the output voltage to 10 V peak-to- peak.
3. Use the Function/Modulation key to select a sine wave.
4. Use the oscilloscope to measure the nns voltage and the period of the sine wave. Enter these values in Table I.
5. Use the digital voltmeter to measure the AC voltage of the sine wave. Enter this value in Table I.
6. Repeat steps 3.4 and 5 for the square wave and the trianeular wave.
7. Compare the meter reading with the oscilloscope reading.

Table 1

Part 2

1. Set the output of the function generator to a 6.3 Vrms with sine wave at a frequency of 75 Hz.
2. Use the oscilloscope to check the rms value and the frequency of the function generator output.

3. Use the digital voltmeter to measure the rms value of the function generator again. Compare this reading to the oscilloscope measurement.

4. Construct the circuit as shown in Figure I.

5. Use the scope to measure the amplitudes of the voltages VAS, Vac. VAC. Record these values. Is the algebraic sum of the first two voltage amplitudes equal to the last? Why not? Does KV!, hold for the AC circuit?

6. Use Ohm's law to calculate the amount of current, I_R1 through the resistor.

7. Use the following formula and your experimental data to calculate la) again. Record and compare these two results.

I_R1= VAC / √{R2 + (1/ ωC)^z}               (1)

Where ω = 2πf is the angular frequency of the voltage in radians per second.

Figure 1: Circuit diagram (a) and Lissajous pattern (b)

Part 3

In this part, we will determine phase difference using oscilloscope. Two different methods are available for using the oscilloscope to determine the phase difference (lag or lead) between two voltages in different parts of the same circuit. The first method consists of measuring the time difference between peak points on the two waveforms. The second method involves a pattern known as a Lissajous figure.

1. To measure the phase difference by the first method, connect channel IX to point A and channel 2Y to point B. with the ground leads of both channels connected to point C.

2. Transport these two waveforms to the computer. Using the program called Run Intuitink Data Capture, capture the image from the oscilloscope to computer.

3. Use the Position knobs to put both waveforms at the center of the display.

4. Use the Display knob to determine the time difference between the peak points on the two waveforms.

5. Calculate phase difference from time difference using following formula (Method On:

θ = 360 x f x Δt Degree                                                   (2)

Enter this value in Table 2.

6. To measure the phase difference by the second method, push the Manu/Zoom key, then select the XY mode.

7. Now an ellipse should appear on the display. Capture this image from scope using Run IntuiLink Data Capture on computer.

8. Push the Cursors key and select the Y I cursor. Then use Push to select key to move the Y1 cursor.

9. Push the Cursors key again and select the Y2 Cursor. Then use the same knob to move the Y2 cursor. The difference between the two cursors will be displayed at the bottom of the oscilloscope screen.

10. The phase difference is calculated using eq. 3 and as depicted in Figure 1 (b) (Method 2):

Sin θ = intersection of ellipse on central axix / maximum vertical extension of ellipse = y₀ / y          (3)

11. By moving the cursor, the value of the intersection of ellipse on central vertical axis and the value of the maximum vertical extension of the ellipse can be determined.

12. Calculate the value of θ, and enter this result in Table 2.

13. The phase angle by which Vac leads V_AC can be calculated directly by the following formula:

Θ = tan-1 (1/ωRC)                (4)

14. Use the formula from equation (4) to calculate the theoretical value of θ, and enter this value in Table 2.

Table 2

By comparing these three values, determine which method gives the more accurate result. From the waveform diagram, which has been obtained above, determine whether VBC leads or lags VAc. Comment on what you think an oscilloscope may be useful for in your field of engineering.