Industrial Electricity PRELAB / LAB 7: Series & Parallel Circuits with Faults Name PRELAB due BEFORE beginning the lab (initials required at the bottom of page 3) PLEASE TAKE THE TIME TO READ THIS PAGE IN ITS ENTIRETY BEFORE STARTING In next week s lab you will construct a both a series and parallel circuit (one at a time). Both circuits will use the same load values (resistors). Once you ve tested the circuits, you will introduce faults and see how the circuit s operation is affected. For the PRELAB work (next two pages) you will calculate the theoretical values of the circuits; first without faults and then with an open load and finally with a shouted load. In the case of the faulted circuits, you may need to use reasoning as much as calculation. We ve discussed this already in lecture, so if you paid attention and/or took some notes, you ll know pretty much what to expect. Then, as in the case of the previous labs, you ll take measurements comparing the measured values with the theoretical values along the way. Once you ve built and verified the values of the circuit without faults, you ll then place faults (shorts & opens, one at time) into the circuit and see how the faults affect the circuit operation, again comparing the theoretical against actual measurements. So as you work through the next two pages, keep a few things in mind: Although there are some calculations to do*, always be thinking, what would I expect to measure with a DMM? This becomes especially important when you start putting faults into the circuit. You have to consider whether the fault will kill the circuit or whether it will just change the values of the voltages, currents, and resistances. As you carry out the thought experiment of what would I measure?, keep in mind that you only have one DMM. That is, you can only make one measurement at a time. Things would get crazy if you could put multiple meters into the circuit at the same time. Let s not go crazy! * I do NOT ask you to show your calculations for the PRELAB, but it might be helpful for your learning. 1
PRELAB needs to be completed prior to building the circuits PRELAB Part 1: Series Circuit with Faults 1. In the space to the right, neatly draw the schematic for a series circuit containing the following components: 9V DC supply = 3kΩ = 10kΩ = 15kΩ 2. Enter the values of voltage, current and resistance you would theoretically measure using a DMM. Calculate the power based on these values. CALCULATED VALUES (No circuit faults) 3. Suppose has burned up, i.e., it has opened. Enter the values of voltage, current and resistance you would expect to measure using a DMM. Calculate the power based on these values. CALCULATED VALUES ( open) 4. Now suppose has been short circuited (bypassed). Enter the values of voltage, current, and resistance you would expect to measure using a DMM. Calculate the power based on these values. CALCULATED VALUES ( shorted) 2
PRELAB Part 2: Parallel Circuit with Faults 5. In the space to the right, neatly draw the schematic for a parallel circuit containing the following components: 9V DC supply = 3kΩ = 10kΩ = 15kΩ 6. Enter the values of voltage, current and resistance you would theoretically measure using a DMM. Calculate the power based on these values. CALCULATED VALUES (No circuit faults) 7. Suppose has burned up, i.e., it has opened. Enter the values of voltage, current and resistance you would expect to measure using a DMM. Calculate the power based on these values. CALCULATED VALUES ( open) 8. Now suppose has been short circuited (bypassed). Enter the values of voltage, current, and resistance you would expect to measure using a DMM. Calculate the power based on these values. CALCULATED VALUES ( shorted) PRELAB COMPLETED Initials: 3
Lab 7: Series/Parallel Circuits with Faults Series Circuit Measured Values NOTE: As you work through the lab always be comparing what you measure with your numbers from the PRELAB. 1. Construct the series circuit from the PRELAB (without faults) and measure the values of resistance, voltage, and current. Enter the values into the table. Note: You will not be able to measure power, so calculate the power (see bottom of page 2) based on the measured values. MEASURED VALUES (No circuit faults) 2. Have your lab instructor supply you with two faulty resistors. Use a meter to determine the one that is open. Replace with the open one. Measure the values of resistance, voltage, and current and enter them into the table. Again, calculate the power based on your measured values MEASURED VALUES ( open) 3. Now Replace with the shorted resistor. Measure the values of resistance, voltage, and current and enter them into the table. Once again, calculate the power based on your measured values. MEASURED VALUES ( shorted) Call the lab instructor over to discuss your results before continuing Initials: 4
Parallel Circuit Measured Values 4. Construct the parallel circuit from the PRELAB (without faults) and measure the values of resistance, voltage, and current. Enter the values into the table. Note: You will not be able to measure power, so calculate the power based on the measured values. MEASURED VALUES (No circuit faults) 5. Obtain two faulty resistors. Use a meter to determine the one that is open. Replace with the open one. Measure the values of resistance, voltage, and current and enter them into the table. Again, calculate the power based on your measured values. MEASURED VALUES ( open) 6. Verify that the other resistor is shorted. Replace with the shorted one. DO NOT APPLY POWER TO THE CIRCUIT!! YOU MAY DAMAGE THE POWER SUPPLY!! Measure the values of resistance and enter them into the table. Calculate the power based on the measured resistance values and the theoretical current and/or voltages. MEASURED VALUES ( shorted) Call the lab instructor over to discuss your results before continuing Initials: 5
Questions in Context Use what you have learned in this lab and previously to complete the following tables and answer the following questions. The figure below shows a series circuit operating under normal conditions when all components are behaving properly. NORMALLY OPERATING CIRCUIT VALUES 2 Meter, measuring circuit current For each set of measurements shown in the table below, identify the defective load (component). Indicate how the load is defective: shorted opened increased or decreased. There is only one defective component for each set of conditions. E 1 (V) E 2 (V) E 3 (V) I T (A) Defective Component 72 48 0 2.4 0 0 120 0 45 60 15 1.5 0 80 40 4 30 60 30 3 18 12 90 0.6 0 120 0 0 90 0 30 3 Nature of Defect 6
The figure below shows a parallel circuit operating under normal conditions when all loads (resistors) are behaving properly. Note: The rectangular boxes are meters reading current, and in one case, voltage. 16 6 120 2.5 7.5 2 4 R 4 For each set of measurements shown in the table below, identify the defective component (resistor or fuse). There is only one defect for each set of conditions. V AG (V) M 1 (A) M 2 (A) Defective Component 120 8.5 6 120 14 4 120 12 2 120 13.5 6 0 0 0 Nature of Defect Note: V AG means the voltage measured if a voltmeter were placed from point A to point G How much voltage would be measured across the fuse if it were: a) open and b) good? How would you measure the resistance of an individual branch of a parallel circuit? List all steps. What precautions must be taken when measuring resistance? If opens, what voltage will be measured across it? How will this open branch affect the current that flows through other parallel branches? 7