Week 1 Lab 2 Oscilloscope Lab

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ECPI University, Virginia Beach *

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Electrical Engineering

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Feb 20, 2024

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Electric Circuits Lab Oscilloscope I. Objectives :  Familiarize with Oscilloscope functions for both Tektronix and native Multisim Oscilloscopes.  Familiarize with function generator.  Use the oscilloscope for DC & AC voltage measurements. II. Parts List :  DC Power Supply, Function generator, DMM, Oscilloscope.  Resistors (1) 1kΩ, (1) 2kΩ. III. Procedures : Part I: Oscilloscope operation: In this section, the instructor will present the theory of operation of the oscilloscope and its main functions in circuit measurements. You may want to refer to the operating manual for detailed explanation of the oscilloscope functions. (Your oscilloscope model may be different than the one shown below) Figure 1. Tektronix Oscilloscope 1

Part II: DC Voltage measurement: 1. Connect the circuit shown in Figure 2. 2. Calculate the current flowing in the circuit, I = 12mA. 3. Calculate the voltage across R 1 , V R1 = 12V 4. Measure the voltage across R 1 using DMM, V R1 = 12V 5. Measure the current flowing in the circuit using DMM, I = .012 A VS 12 V R1 1.0kΩ Figure 2. Circuit Diagram 6. Turn on your oscilloscope. 7. Set the coupling to ‘GND’, as shown in Figure 3. Figure 3. Oscilloscope screen with GND Coupling 8. Connect CH1 probe across the resistor. Make sure the ground lead is connected to the power supply ground. 9. Set CH1 VOLTS/DIV to 5VOLTS/DIV. 2

10. Set CH1 coupling to ‘DC’. 11. The waveform observed should be similar to Figure 4. Figure 4. Oscilloscope screen with DC measurement 12. Measure the voltage across R 1 using oscilloscope, V R1 =11.8V 13. Modify the circuit by placing 2kΩ resistor in series with 1kΩ, as shown in figure 5 below. VS 12 V R1 1.0kΩ R2 2kΩ Figure 5. Series circuit 14. Measure the voltage across R 1 using oscilloscope, V R1 = 4V 15. Measure the voltage across R 2 using oscilloscope, V R2 = 8V 3

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Part III: AC Voltage measurement: 1. Set your function generator to a 1 Vrms. sinusoidal waveform with a frequency of 1 kHz. 2. Calculate the peak-to-peak voltage for this waveform. V pk-pk =2V 3. Measure the signal voltage using your DMM, V s (DMM) =1V 4. Connect your oscilloscope to the function generator. 5. Adjust the scope to display the waveform as shown in Figure 6 below. Figure 6. Oscilloscope screen with AC measurement 4

Assignment:  Change the settings of your VOLTS/DIV for CH1 to 1 VOLT/DIV  Count the vertical divisions.  Calculate the peak-to-peak voltage:  V pk-pk = (Number of divisions) x (Volts/DIV)= 2.3 V  Change the settings of your VOLTS/DIV for CH1 to 2 VOLT/DIV  Count the vertical divisions  Calculate the peak-to-peak voltage:  V pk-pk = (Number of divisions) x (Volts/DIV)= 2V  Change the settings of your SEC/DIV to 200µs/DIV  Count the horizontal divisions for one cycle  Calculate the time period:  T= (Number of divisions) x (SEC/DIV)= 2.4ms  Calculate the frequency 416 hz.  Change the settings of your SEC/DIV to 1ms/DIV  Count the horizontal divisions for one cycle  Calculate the time period:  T= (Number of divisions) x (SEC/DIV)= 3ms  Calculate the frequency 333hz.  Compare your results to the automatic ‘Measure’ function of the scope.  Use the cursor function on the scope to measure the peak-to-peak voltage and period. Part IV: AC Voltage measurement: 1. Modify the circuit by replacing the DC source with the AC Power source as shown in figure 7 below. R1 1.0kΩ R2 2kΩ VS 1 Vrms 1kHz 0° Figure 7. Series circuit 2. Measure the peak voltage across R 1 using oscilloscope, V R1 = 941mV 3. Measure the peak voltage across R 2 using oscilloscope, V R2 = 1.88 V Part V: The Native Multisim Oscilloscope 5

1. Connect the circuit shown in Figure 8. Set the function generator to a sinusoidal waveform with a frequency of 100 Hz, a peak amplitude of 10 V P , and 0 V DC offset. Figure 8. Series Circuit 2. Place the oscilloscope and digital multimeter (DMM) as shown in Figure 9. The DMM should be set to read AC volts. The oscilloscope should be set to 5 ms/Div under time base and 2 V/Div for Channel A. It should also be set to AC mode. Figure 9. Test equipment setup 3. Run the Multisim simulation and record the DMM reading. DMM Reading: 3.535 V 6

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4. Measure the period (T), amplitude of peak voltage (V p ), amplitude of peak-to-peak voltage (V pp ). 5. Set the function generator to each value listed in Table 1. You will have to change both the vertical and horizontal scales to make the measurements. Record the number of vertical oscilloscope divisions the signal is deflected, the peak voltage (using the cursors), and the peak-to-peak voltage (using the cursors). Finally, record the DMM reading. Function Generator Settings Oscilloscope DMM Voltage Frequency Voltage, V p Volts/ Div Deflection V p V pp V RMS 100 Hz 10 V 2 5 Div. 4.992 V 9.985 V 3.535 V RMS 500 Hz 20 V 5 5 Div 9.985 V 19.976 V 7.071 V RMS 1 kHz 30 V 10 10 Div 14.874V 29.756V 10.606 RMS 2 kHz 50 V 10 10 Div 24.887V 49.696V 17.676V RMS Table 1. AC Oscilloscope Measurements Part VI: Understanding DC Offset and AC and DC measurement modes 1. Modify the circuit in Figure 9 to include a second DMM and connect Channel B of the oscilloscope across R 2 . 2. Set the function generator to a frequency of 1 kHz, Amplitude 5 V P , and Offset 5 V. 3. Set one DMM to read AC volts and one DMM to read DC volts. 4. Set the oscilloscope time base to 500 µs/Div. Set Channel A settings to 2 V/Div and AC mode. Set Channel B settings to 2 V/Div and DC mode. 5. Run the simulation and place your screenshot below. 7

6. 7. Explain what you observe and why for the following settings: a. DMM AC mode: This multimeter is reading the voltage drop across R1 in VRMS. b. DMM DC mode: This multimeter is DC mode can only measure current flow in one direction, which is why it shows half of the AC supply voltage. c. Oscilloscope AC mode: The sine wave in AC mode stays centered on the x- axis d. Oscilloscope DC mode: With the offset applied the sine wave of the DC channel is moved above the x-axis, which prevents opposite current flow from showing on the oscilloscope 8