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ECE 211 Electrical Circuits Lab I LAB #5 Section Name Delta/Wye Conversions and the Wheatstone Bridge OBJECTIVE: 1. To become familiar with delta to wye conversions and its usefulness in circuit analysis 2. To understand the behavior of the Wheatstone bridge. 3. To measure resistors using the Wheatstone bridge. COMPONENTS AND EQUIPMENT: 1. 2. 3. 4. Digital multimeters (2) Variable DC supply. Leads Resistors BASIC Δ-Y TRANSFORMATION The transformation is used to establish equivalence for networks with 3 terminals. Where three elements terminate at a common node, the node is eliminated by transforming the resistances. For equivalence, the resistances between any pair of terminals must be the same for both networks. RC R2 R1 Rb Ra R3 1 ECE 211 Electrical Circuits Lab I LAB #5 Transformation from Δ-load to Y-load Transformation from Y-load to Δ-load PROCEDURE EXPERIMENT 1 In this part of the experiment, you will construct a delta configuration of three resistors, measure and record terminal resistance, and design and construct an equivalent wye configuration. 1. Build the circuit of Figure 1. DO NOT APPLY ANY POWER SUPPLIES Figure 1 Ra= 3.3 K Ω Rb= 5.6 K Ω Rc= 4.7 K Ω 2. Measure and calculate the resistance between the terminals of your delta configuration. Compare both values and explain the differences. 3. Use the delta /wye conversion formulas given above to design an equivalent wye configuration. 4. Build the wye configuration. You can use two resistors in series for each of the calculated resistors to get a closer value. Verify that it has the same behavior as the delta configuration. 2 ECE 211 Electrical Circuits Lab I LAB #5 EXPERIMENT 2 In this part of the experiment, you will substitute the original delta configuration for the wye configuration. This substitution will verify that the delta-to-wye substitution is valid. 1. Calculate and measure Rin. 2. Calculate R6, R7 and R9 in order to make configuration A and B equivalent. 3. Connect the circuit in configuration B (you may use series resistors to get closer values for R6, R7, and R9). Measure the input resistance of Configuration B. Is it the same as configuration A? 3 ECE 211 Electrical Circuits Lab I LAB #5 EXPERIMENT 3 The G in the circuit above is a voltmeter. It measures the voltage drop between A and B. 1. Set R1 and R2 to 1K. Put a potentiometer where Rk is, and pick a random resistor as Rx (in order of KΩ). Set Vo to 5 V. Change the value of the potentiometer until the voltmeter reads “0”, now the bridge is balanced, and the resistances relation will be: Rx/Rk=R2/R1 Calculate the value of Rx. Compare this value with the value of the resistance measured with an ohmmeter. 2. Set R1 to 2K. Compute Rx again. Does it have the same value as before? 3. Change the value of Vo and compute the resistance again. Does the voltage affect the measurement of the resistor? 4