Lab 16 Parallel RL Circuits On line Leon M 17Mar2020

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Apr 3, 2024

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Lab 16 (eBook 25) Parallel RL Circuits (simplified) Name _Neelmani bhardwaj___________________ Date ___________________ Class ___________________ READING Text, Sections 12–4 through 12–9 OBJECTIVES After performing this experiment, you will be able to: 1. Determine the current phasor diagram for a parallel RL circuit. 2. Measure the phase angle between the current and voltage for a parallel RL circuit. 3. Explain how an actual circuit differs from the ideal model of a circuit. MATERIALS NEEDED Resistors: One 3.3 kΩ, two 47 Ω, One 100 mH inductor REQUIRED LAB PREPARATION (PRELAB) 1. Read all sections of the lab. 2. READ document named “BRIGHTSPACE ON-LINE LAB ASSIGNMENT AND SUBMISSION PROCEDURE” available in Lab 11 folder 3. Read the text book, sections 12-44 through 12-9 4. Find the required resistor and inductor for this lab as indicated in the Materials Needed section above 5. Review the differential probe measurement and phase measurement techniques from Labs 8 and 14. 6. Review the oscilloscope time “base operation” or what is called Horizontal Control depending on the oscilloscope manufacturer. 7. All Voltage and Phase angle measurements are performed with the oscilloscope. No DMM . Fall 2015 Lab 16 P a g e | 1

8. Complete the PreLab questions at the back of this document and hand in to teacher before going to your Lab station the back of this document and hand in to teacher before going to your Lab station SUMMARY OF THEORY The parallel RC circuit was investigated in Experiment 12. Recall that the circuit phasor diagram was drawn with current phasors and the voltage phasor was used as a reference, since voltage is the same across parallel components. In a parallel RL circuit, the current phasors will again be drawn with reference to the voltage phasor. The direction of the current phasor in a resistor is always in the direction of the voltage. Since current lags the voltage in an inductor, the current phasor is drawn at an angle of −90° from the voltage reference. A parallel RL circuit and the associated phasors are shown in Figure 16–1 . Figure 16–1 Practical inductors contain resistance that frequently is large enough to affect the purely reactive inductor phasor drawn in Figure 16–1 . The resistance of an inductor can be thought of as a resistor in series with a pure inductor. The effect on the phasor diagram is to reduce an angle between I L and I R . In a practical circuit this angle will be slightly less than the −90° shown in Figure 16–1 . This experiment illustrates the difference between the approximations of circuit performance based on ideal components and the actual measured values. Recall that in Experiment 15, the phase angle between the source voltage, V S , and the resistor voltage, V R , in a series circuit were measured. The oscilloscope is a voltage-sensitive device, so comparing these voltages is straightforward. In parallel circuits, the phase angle of interest is usually between the total current, I T , and one of the branch currents. To use the oscilloscope to measure the phase angle in a parallel circuit, we must convert the current to a voltage. This was done by inserting a small resistor in the branch where the current is to be measured. The resistor must be small enough not to have a major effect on the circuit. Fall 2015 Lab 16 P a g e | 2

PROCEDURE 1. See document titled” BRIGHTSPACE assignment and submissions process” which is available in Lab 11 folder, 2. These include a. Simulate the circuit in Multisim and record the required results in the appropriate table, b. Paste into a blank sheet an image of your actual breadboard as if you were doing the experiment in the Lab, and c. Submit this completed Lab document, and the simulation files via the assignment folder in Brightspace. 3. Record the results as required in Table 16-1 . Construct the circuit shown in Figure 16–2 . Notice that the reference ground connection is at the low side of the generator . This connection will enable you to use a generator that does not have a “floating” common connection. Using your oscilloscope, set the generator to a voltage of 6.0 V pp at 5.0 kHz. Check both the voltage and frequency with your oscilloscope. Record all voltages and currents in this experiment as peak-to- peak values. Listed Value Measured Value Show as many significant digits as possible on your best measuremen t range Voltage Drop Show V or mV and as many digits as possible Computed Current Ohm’s law, mA R 1 (Ir) 3.3 kΩ 5.91v 1.79 mA R S 1 (It) 47 Ω 122.67mV 2.61mA R S 2 (I L ) 47 Ω 88.16mV 1.87 L 1 100 mH _______mH Same as R S2 R W ( L 1 resistance) _______ Ω Fall 2015 Lab 16 P a g e | 3

in Ω Table 16–1 Figure 16–2 4. Using the oscilloscope , measure the peak-to-peak voltages across R 1 , R S 1 , and R S 2 . Use the two-channel difference method (described in Experiment 8) to measure the voltage across the two ungrounded resistors. Apply Ohm’s law to compute the current in each branch. Record the measured voltage drops and the computed currents in Table 16–1 . Since L 1 is in series with R S2 , enter the same current for both . 5. The currents measured indirectly in step 4 are phasors because the current in the inductor is lagging the current in R 1 by 90°. The current in the inductor is the same as the current in R S 2 , and the total current is through R S 1 . Using the computed peak-to-peak currents from Table 16–1 , draw the current phasors for the circuit on Plot 16–1 . (Ignore the effects of the sense resistors.) Phase Angle Between: Computed Measured I T and I R 46.25 43.75 I R and I L 90° 90 I T and I L 43.2 46.25 Fall 2015 Lab 16 P a g e | 4

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