Parallel Resistive Circuits Troubleshooting Student Name: Lab Station: Introduction: Troubleshooting circuits requires knowledge of Ohm’s law and Kirchoff’s voltage and current laws as a minimum. Two things you have to keep in mind are that an open circuit will carry no current but will have the full open circuit voltage across it, and a short-circuited component will have no voltage across it but will carry the total series current through it. In this lab the student will thoroughly examine isolated Faults on three resistor current dividers. Faults will be introduced, and measured currents will be compared to calculated (expected) results. Calculated results are essential prior to building and testing the circuit to ensure a good understanding of the fault conditions in question. Materials: 1 DMM (Digital Multi—Meter) 1 dc power supply 1 19 ohm 5% Resistor (R4) (Simulates short) 1 1 M ohm 5% Resistor (R5) (Simulates open) 1 195 ohm 5% Resistor (R6) 1 29 k ohm 5% Resistor (R7) 1 38 k ohm 5% Resistor (R8) 1 47 k ohm 5% Resistor (R9) Kirchoff’s Current Law states: ‘The sum of the currents into a junction (total current in) is equal to the sum of the currents out of that junction (total current out).’ IT = I1 + I2 + I3 m Kirchoff’s Voltage Law states: ‘The sum of all the voltage drops around a single closed path is a circuit is equal to the total source voltage in that loop.’ Vs = V1 + V2 + V3 Conductance: Reciprocal of resistance symbol (G). Unit is siemens(5) Branch: A single current path in a parallel circuit. Node: Point where two or more conductors are connected. Current Divider: A parallel circuit in which the currents divide inversely proportional to the parallel branch resistances. FIE Aw,— {1:23 'l??ol'urn 1:; HT HE. REI- — I?kohm :HIl-mhm #TI-mhm Figure 1: Parallel Circuit for Lab 7b)

Part I — Parallel Circuit with Short Circuits 1. For the circuit shown in Figure 2, calculate the nominal values oF current 1, 11, I23, 12, and 13 and write them in table 1. 2. Assume that R7 (only) becomes short-circuited. we will use 16 ohms in parallel with the resistor to simulate a short. Re—calculate the currents I, 11, 123, 12, and 13 and write them in table 1 below. 3. Repeat the calculation For step 2 For R8 shorted, then R9 shorted. Complete Table 1. Table 1 — Calculated Current Values without and with Faults Calculated Calculated Currents with One Resistor Shorted 160 in narallel Values (no fault) R7 Only Shorted R8 Only Shorted R9 Only Shorted 4. Now construct the circuit shown in Figure 1. Adjust the power supply so there is 16 volts across R7. The 166 ohm resistor (R6) is there to provide current protection to the supply. IF the power supply is current limiting, set it to 166 mA. 5. Measure the current 1 and record it in the table below. Add 16 ohms (R4) in parallel with R7 and measure 1 again. The 16 ohm vaLue is used to simuLate a short circuit. Repeat this step, three times, shorting R7, then R8, and then R9 with the 16 ohm resistor, one at a time. 6. Now remove the short and set your meter up to measure 11. Record the value in table 5. Repeat this step, three times, adding the short across R7, R8 and Finally, R9. 7. Repeat step 6 For 123, 12, and 11 Table 2 — Measured Current Values without and with Faults Measured Values Measured Currents with One Resistor Shorted Current (no Fault) R7 Only Shorted R8 Only Shorted R9 Only Shorted Calculate the percent diFFerence between what you calculated and what you measured, using this Formula: % diFFerence = (measured — calculated)/calculated x 166% Complete table 3. Table 3 — DiFFerence Between Calculated and Measured No Fault and with Short-Circuits No Fault Values Percent DiFFerence, Measured vs. Calculated (% diFFerence) R7 Only Shorted R8 Only Shorted R9 Only Shorted DO NOT DISASSEMBLE THE CIRCUIT

Part II — Parallel Circuit with Open Circuits 1. Assume that R7 (only) becomes open—circuited. Re—calculate the currents I, Il, 123, IZ, and I3 and write them in table 1 below. 2. Repeat step 2 for R8 and R9. Also record these values in Table 1. Table 4 — Calculated Current Values without and with Faults Calculated Currents with One Resistor Open Calculated Values—no (Replaced with 1M0) Current fault, from table 1 R7 Only Open R8 Only Open R9 Only Open I Ii I23 12 Is 3. REMOVE ANY SHORT YOU MAY HAVE LEFT IN PLACE FROM PART 1. Verify that there is still 16 volts across R7. A 1 MD vaLue is used to simuLate an open circuit as its vaLue is so much Larger than the original resistors. A true open circuit aLLows no current to flow but using this method provides some current. 4. Measure the current I and record it in table 5. Repeat this step three times, replacing R7, R8 and R9 with the open circuit (1 MO) one at a time. 5. Now set your meter up to measure I1. Record the value in table 5. Repeat this step three times, replacing R8 and R9 with the open circuit (1 MO) one at a time. 6. Repeat step 5 for I23, 12, and I1 Table 5 — Measured Current Values without and with Faults Measured Currents with One Resistor Open Measured Values—no Re-laced with 1M0 Current fault R7 Only Open R8 Only Open R9 Only Open I Ii I23 I2 I3 Calculate the percent difference between what you calculated and what you measured, using this formula: % difference = (measured — calculated)/calculated x 166% Complete table 6. Table 6 — Difference Between Calculated and Measured, No Fault and with Open Circuits No Fault Values Percent Difference, Measured vs. Calculated (% difference) R7 Only Open R8 Only Open R9 Only Open Current THERE IS A QUESTION 0" THE NEXT PAGE

Write a few short sentences explaining what you learned in this lab and how you could apply it to troubleshooting an actual circuit board.

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