Lab III - Network Laws Rev1 2023

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University of Maryland, Baltimore County *

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306

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Electrical Engineering

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Dec 6, 2023

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CMPE 306 Lab III: Network Laws, Current and Voltage Measurements Created by: E.F.C. LaBerge based on previous unattributed lab description July 2013 Revised Fall 2016 E. F. C. LaBerge and Aksel Thomas Revised for Keysight Equipment E.F.C. LaBerge, July 2023, Sept 2023

1 1. Purpose and Introduction The purpose of this second lab exercise for CMPE306 is to expose the student to the physical manifestations of the basic network laws: Ohm’s Law, Kirchoff’s Current Law (KCL) and Kirchoff’s Voltage Law . This lab includes a pre-lab exercise, discussed in Section 2. This lab requires the basic equipment skills presented and practiced in Lab I. Students should review those skills especially the procedure for non-destructive measurement of current before starting this lab. In this lab, you will be required to build various circuits using the breadboards and parts from your lab kit. By the successful conclusion of this lab, students will have observed the following features of linear DC circuits: 1. Ohm’s Law 2. Kirchoff’s Current Law 3. Kirchoff’s Voltage Law 4. The fact that a series combination of resistors operates as a voltage divider. 5. The fact that a parallel combination of resistors operates as a current divider. 6. The reciprocal sum characteristic of parallel resistors. 7. The computation of the virtual mesh currents used in mesh analysis. The lab report in standard format is due at the start of next week’s lab session. Spelling, grammar, coherence, content and formatting all count. 2. Pre-lab The pre-lab for this lab exercise consists of the following task: 1) LTSPICE (or equivalent) simulation of the circuits in Figure 1 through Figure 5 of this lab. Some of these circuits are simple modifications of the circuits simulated during Lab II, so if you saved your circuits from last week, you should be nearly complete with this portion of the pre-lab. During this simulation exercise, pay particular attention to the signs of the currents! What happens to the sign if you rotate the component (with <CTRL> R) by ? Keep this in mind as you create the circuits. You should spot check the lab computations with your circuit simulations before you get to class. Have your lab assistant certify your simulation results prior to starting to construct your circuit. 180 °

2 3. Equipment 1. Keysight triple power supply. We will use both the yellow and green supply voltages. 2. Keysight digital multimeter 3. Two sets of banana-alligator patch cords (two each red and black or two double banana plugs) 4. Breadboard 5. Resistors from lab kit: . Hint 1: Resistor color code from 0 to 9: Bk-Br-R-O-Y-Gn-Bl-V-Gr-W. Hint 2: Figure out the color codes for these resistors (you already know that 1kΩ is brown-black-red) and then check their values with the multimeter. 6. Miscellaneous wires from lab kit. 7. You may want to record data directly into Excel or Word or their equivalents. If so, you will need a laptop or the lab computer. Don’t forget to save your work to a USB stick if you are using the lab computer so that you have the data to complete your report. 4. Procedure There are five parts to today’s lab, so you need to move smartly. If you get hung up, ask for help so that you don’t fall behind. Before you start exercise 4.1, use the multimeter to measure and record the actual values of all four resistors. Answers to the nearest ohm are sufficient: fractional ohms won’t change the computations in any meaningful way. (See Hint in the parts list, above.) 4.1. Ohm’s Law and Voltage Division Figure 1 Circuit for Ohm’s Law and Voltage Division 1. Using a resistor, wire together the circuit shown in Figure 1. You will need to use the green output of the Keysight power supply to create the 12V source, because the yellow supply we used in Lab I is limited to 6 V maximum. The setup is the same, just select the green 2 button and use the green On button. When setting the voltage to 12 V, also set the current to 510 Ω , 1k Ω , two 2k Ω V1 12V R2 2kohm R1 1kohm .op 1k Ω and a 2k Ω

3 0.250 A. ( Hint: Except for the value of the second resistor, this is the same circuit you built in the last task of Lab I . Go back and look at how you built that circuit .) 2. Be careful! Follow the process for measuring current defined in Lab I. Current must always be measured in series! ( Hint: Remember that measuring current requires a reconfiguration of the red probe connection on the multimeter ). Configure the multimeter for current measurement and follow the procedure from Lab I to measure and record the current flowing from the power supply to the breadboard, and the current flowing between R1 and R2. 3. How are the resistors connected in this circuit? Using the measured values of the resistors, verify a) Ohm’s Law, , and b) KCL for the series circuit. 4. Compute the ratios . Multiply these ratios by the supply voltage and compare the results with the voltage measured across , respectively. 5. Add the resistor in series with the resistor and call this . Measure and record the current flowing between the resistor and the resistor. Why is this value different from that recorded in Step 3? Using the measured values of the resistors, reverify Ohm’s Law and KCL. 6. Be careful! Reconfigure the multimeter setting to measure voltage by moving the red probe to the appropriate voltage and resistance measuring position before this step! Select DCV (voltage) or ࠵? 2 W (resistance) before measuring. Voltages must be measured in parallel with the resistors. Measure the voltage drop across all three of the resistors. Use these measured values to verify KVL for this circuit. 7. Compute the ratios . Multiply these ratios by the supply voltage and compare the results with the voltage measured across , respectively. 8. Change the green voltage on the Keysight power supply to 15V and repeat steps 2 through 7. Be careful when you go back to measuring current. Reconfigure the multimeter and be sure to use the right current measuring procedure. BE CAREFUL! 9. Turn off the power supply output and construct the circuit for 4.2, below 4.2. Ohm’s Law and Current Division 1. Using all four resistors, wire together the circuit shown Figure 2. As in the previous section, you will need to use one of the +30V outputs (either the Green output or the Blue output) of the Keysight power supply to create the circuit. V = IR R 1 R 1 + R 2 and R 2 R 1 + R 2 R 1 and R 2 510 Ω 2k Ω R 3 2k Ω 510 Ω R 1 R 1 + R 2 + R 3 , R 2 R 1 + R 2 + R 3 and R 3 R 1 + R 2 + R 3 R 1, R 2 and R 3

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