advertisement

ECE207 Electrical Engineering Fall 2011 - 2012 Lab 2 Phasor Measurements Objectives: At the conclusion of this lab, students should be able to: use the NI myDAQ to measure phasor voltage use the NI myDAQ to measure phasor current use a shunt to measure the current through a capacitor Equipment: Laptop with NI myDAQ software installed NI MyDAQ breadboard 1 - 1 k resistor 1 - 2 k resistor 1 - 10 resistor 1 - 33 mH inductor 1 - 0.1 F capacitor Procedure Part 1: Voltage Measurements 1. In this part, you will use the oscilloscope to measure AC voltages. If you need a refresher on using the NI my DAQ instruments, please review the documentation in the box and the tutorials at the following links: Introduction to NI myDAQ: http://decibel.ni.com/content/docs/DOC-13041 DMM – ohmmeter: http://decibel.ni.com/content/docs/DOC-12880 Analog Output and Input: http://decibel.ni.com/content/docs/DOC-12884 2. Use the LCR meter provided in the classroom to measure the inductor and capacitor and record their values on the table in the worksheet. 3. Launch the NI ELVISmx Instrument Launcher from the National Instruments folder and you should see the toolbar appear on your desktop. 4. Use the ohmmeter to measure each of the resistors and record their values on the table in the worksheet. CAB Lab2.docx 1 ECE207 Electrical Engineering Fall 2011 - 2012 5. Use nodal analysis, to find each of the labeled values on the circuit in Figure 1. Make sure that you use the measured values of the components in your calculation. Show the calculations on the space in the worksheet and record the values in the table. Express your answers as phasors with the magnitude in RMS and the phase angle in degrees. Figure 1: Phasor Circuit 6. Make sure that the breadboard is horizontal with the red buss across the top. Build the circuit in Figure 1 with the ground on the blue buss at the bottom of the breadboard. 7. Connect the NI myDAQ function generator (AO 0, 1) to the left side of the 1 k resistor and the ground buss. Connect Ch. 0 of the oscilloscope (AI 0+, 0-) to measure the function generator on the circuit. 8. Connect Ch. 1 of the oscilloscope (AI 1+, 1-) to measure v1, across the 0.1 F capacitor. 9. Click on FGEN to open the function generator on the NI myDAQ and set it to 8.5 Vpp, 1.0 kHz sine wave. Click run on the function generator 10. Click on Scope button to open the NI MyDAQ oscilloscope. Set both channels to 1 V/div, 100 s/div, trigger type Edge, Chan 0 Source, positive slope. Make sure the source on Channel 0 is AI 0 and the source on Channel 1 is AI 1. Click run on the oscilloscope. 11. If you have set up the circuit and instruments correctly, your system should look similar to Figure 2. If it does not, please do not move on until you check your work and solve the problem. CAB Lab2.docx 2 ECE207 Electrical Engineering Fall 2011 - 2012 Figure 2: Oscilloscope and function Generator Settings 12. Use the voltmeter to measure the magnitude of the node voltages in V rms and record the values on the table in the worksheet. Recall that the percent error formula is 13. Use the cursors and time axis crossings to estimate the phase angle similar to what you did in Lab 1. Please go back and review Lab 1 if you don’t recall how to do this. Record the measured phase angles on the table in the worksheet. Note that the error for a phase angle is a difference not a percent so use the following: Part 2: Current Measurements 1. In this part, you will measure phasor current. Since the oscilloscope only measures voltage, you will use voltages and measured resistor values to find current. 2. Use the measured voltage of the source and V1 to find the voltage drop across the 1 k resistor using the following formula: 3. Use the measured values of V1 and V2 to find the voltage drop across the 2 k resistor. Use the voltage across the resistor to find the current, I2, using the following formula: 4. Record the current magnitudes and phase angles on the table in the worksheet and perform the error analysis. CAB Lab2.docx 3 ECE207 Electrical Engineering Fall 2011 - 2012 5. It is necessary to do a little bit more work to find the current through the capacitor. It is necessary to put a 10 resistor as shunt in series with the capacitor as shown in Figure 3. Figure 3: Capacitor with shunt resistor 6. Use the oscilloscope to measure, Va, the voltage across the resistor. Note that this signal will be very small and you will have to turn Channel 1 up to 10 mV/div. Finally, use the following formula to find I3: 7. Record the magnitude and phase of I3 on the data table and perform an error analysis. 8. You have now completed Lab 2 and should confirm that you have included all of the required information on the worksheet. Submit the worksheet to the instructor by the end of the lab session. CAB Lab2.docx 4 ECE207 Electrical Engineering Fall 2011 - 2012 Lab 2 Phasor Measurements WORKSHEET NAME: ________________________________________________________ NAME: ________________________________________________________ Part 1: Voltage Measurements Table 1: Component Values (include all units) element measured nominal % error Nodal Analysis calculation on Figure 1: CAB Lab2.docx 5 ECE207 Electrical Engineering Fall 2011 - 2012 Table 2: Voltage Measurements (include all units) component measured nominal error | V1| V1 | V2| V2 Part 2: Current Measurements I1 calculation from measured voltage and resistance: I2 calculation from measured voltage and resistance: I3 calculation from measured voltage and resistance: CAB Lab2.docx 6 ECE207 Electrical Engineering Table 3: Curent Measurements (include all units) component measured nominal Fall 2011 - 2012 error | I1| I1 | I2| I2 | I3| I3 CAB Lab2.docx 7