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Lab 3: Equivalent Networks and Superposition Page 1 Lab 3: Equivalent Networks and Superposition Theory & Introduction –Goals for Lab 3 –For this lab you will be exploring some of the circuit solving techniques you have been studying in lecture. Specifically, you will build two DC circuits to experimentally test these concepts. The first procedure will verify Thévenin's equivalent circuit. The second procedure will verify the superposition principle. After you verify that the superposition principle works, you will also test the conditions under which Superposition can be applied. In this lab, you will also learn more about how PSPICE can be used to model a circuit. Theory –Equivalent Circuits –As you have learned in lecture, circuits can be transformed to equivalent circuits to ease in analysis. In sections 4.10 and 4.11 of your text, Thévenin and Norton Equivalents are explored. In this lab, we will focus on the Thévenin equivalent circuit shown below in Figure 3.1.a. Remember that you can always use a source transformation to move from the Thévenin equivalent to the Norton Equivalent circuit shown in Figure 3.1.b and vice versa. Figure 3.1a: Thévenin's Equivalent Circuit Figure 3.1b: Norton’s Equivalent Circuit
Lab 3: Equivalent Networks and Superposition Page 2 Review of measuring Current and Voltage –It is important you remember how to measure voltage and current. You need to measure current in series with the element you want to know the current through. You need to measure voltage in parallel with the element you want to know the voltage over. In addition, for the NI ELVIS DMM, you need to make sure the proper nodes are used to measure current. For the HP DMM, you need to make sure the plug is in the top two holes for voltage and the bottom two holes for current. You can review pages 6-12 of Lab 1 where using the equipment is described in detail. Superposition –The Superposition principle should have been covered in lecture by this time. If you need more detail on it before beginning this lab, please read the appropriate sections of your text. Simply put, superposition holds that if you have a linear circuit with multiple independent sources, you can solve the circuit by solving a circuit with each source in the circuit alone. Then, summing the individual results, with respect to polarity, should give you the same result as if you solved the circuit with all independent sources present. In this experiment, you will be testing this principle. Linear versus non-linear devices –So far, you have encountered mainly resistors when building circuits. Resistors are generally modeled as linear devices in this course. However, there are other devices that are non-linear. Operational Amplifiers have both a linear and a non-linear range of operation.