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Fundamentals of Wireless and Routing Technology
Lab 1
Analysis and Troubleshooting Basic Electric Circuit
Objective :
To gain experience in troubleshooting Electric Circuit.
Equipment :
1. DC Power Supply.
2. VOM or DMM or Scope.
3. Power leads, breadboard, lab kit, connecting wires.
Lab 1 – Pre – Lab
For the circuits shown, calculate the values shown in the tables below. Show all your
calculations.
Table 1:It
VR1
R1
1
Quantity
2
8.2kΩ
V2
10 V
VR2
VR3
R3
4
R2
3.3kΩ
3
1.5kΩ
Circuit 1
Calculated
(Ohm’s Law)
Calculated
using Voltage
Divider Rule
RT
IT
VR1
VR2
VR3
Table 2:Quantity
It
5
V1
10 V
Ir1
R1
8.2kΩ
6
Circuit 2
Ir2
R2
3.3kΩ
Ir3
R3
1.5kΩ
RT
IT
VR1
VR2
VR3
IR1
IR2
IR3
1
Calculated using
Ohm’s Law
Calculated using
Current Divider
Rule
Table 3:It
Ir1 12
R2
3.3kΩ VR2
R1
8.2kΩ
V3
10 V
10
R3
1.5kΩ VR3
11
Cricuit 3
Quantity
RT
IT
VR1
VR2
VR3
IR1
IR2
IR3
Calculated
Table 4:It
8
R1
6
1.5kΩ
R2
3.3kΩ
V4
10 V
7
R4
1.5kΩ
Circuit 4
5
Quantity
RT
IT
IR1
R3
8.2kΩ IR2
IR3
IR4
VR1
VR2
VR3
VR4
Calculated
Part A – Series Circuit
Procedure :
1. Construct the circuit shown below and adjusted to be exactly 10 V using a VOM or
DMM.
2. Enter your calculated values from Pre-lab in Table 1 on the next page.
2
Table 1:R1
4
3
Quantity
8.2kΩ
V1
10 V
R2
3.3kΩ
V
R3
1
2
1.5kΩ
Fig 1
Calculated Measured
(Enter
Pre-Lab)
Calculated
using
Voltage
Divider Rule
RT
IT
VR1
VR2
VR3
3. Now measure the voltage drops on each of the 3 resistors and enter into the measured
values section of the table.
4. Compare the measured values with your calculated values. Do they agree? If not, then
either your measured values are incorrect or the calculated values are wrong. Recheck
and repeat steps 2 and 3 until your measured and calculated values are the same.
5. Add up your calculated and measured voltages. According to the kirchoff’s voltage law
the sum of all voltage drops must equal the applied voltage E. Is that true in your case.
Comment on your result.
6. Indirect Measurement of Current
8
R1
7
8.2kΩ
V2
10 V
R2
3.3kΩ
11
V
6
R3
5
1.5kΩ
Fig 2:- Break Simulation
Measure the voltage drop on any one of the 3 resistors and divide this measurement by
the value of the resistance. Since current is the same throughout a series circuit, it
doesn’t matter which resistor you use. This is just an application of OHM’s law. To
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improve the accuracy of this measurement, measure the actual value of the resistor.
This indirect measurement technique for current is much more useful and easier to
perform then breaking the circuit and inserting an ammeter. Use it from now on for
measuring current unless told otherwise.
7. Compare the measured and calculated current values.
8. Simulate a break in the circuit by removing the wire between R2 and R3.
9. Measure IT, VR1, VR2 and VR3. As well as the voltage across the break. To measure the
voltage across the break, connect voltmeter between R2 and R3.
10. Enter your results in the table below.
Simulated Break Results
IT
VR1
VR2
VR3
11. Based on your observations of the result above, state 3 most important facts about
open circuit faults in a series circuit.
12. Use voltage divider rule to calculate VR1, VR2, VR3. Show your calculations. Compare
these calculated values with the values calculated in step 2. And your measured values.
Do they match? Comment.
Part B – Parallel Circuit
Procedure :
1. Build the circuit shown below and adjust the power supply to be exactly 10V.
It
10
V3
10 V
R1
8.2kΩ
R2
3.3kΩ
R3
1.5kΩ
9
4
2. Enter your calculated values from Pre-Lab for this circuit in Table 2 below.
3. Measure IT, VR1, VR2, VR3, IT1, IT2 and IT3. Enter your measurements in the table.
Quantity
Table 2:Measured
Calculated using
Current Divider
Rule
Calculated
Fault Simulated
Values
IT
RT
VR1
VR2
VR3
IR1
IR2
IR3
4. Your calculated and measured values should agree. If not, repeat steps 2 and 3 until
they match.
5. Add up I1, I2 and I3. According to KCL the sum of all branch currents must equal I T.
Verify KCL for both the calculated and measured values.
6. Knowing it, use current divider rule to calculate branch currents, I1, I2 and I3. Compare
with calculate values in step 2 and measured values in step 3.
7. Simulation of Open Circuit Fault in a Parallel Circuit
Original circuit is redrawn below.
2
V1
10 V
A
R1
8.2kΩ
R2
3.3kΩ
3
A
B
1
R3
1.5kΩ
B
Introduce a break at point A (You can do that by either lifting the resistor at point A or
by removing the wire that connects the bottom bus to R2 at A).
8. Measure IT, I1, I2, I3, VR1, VR2 and VR3. Enter these values into the table.
9. Based on your simulated results, state 3 basic facts about open circuit faults in Parallel
circuit.
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10. Can you introduce a short across points A and B? (Don’t try to do that). What will
happen?
Part C – Series Parallel Circuit
Procedure:
1. Enter the calculated values from Pre-Lab for this circuit in Table 3 below.
Table 3:It
3
Ir1
V1
10 V
R1
8.2kΩ
Ir2
R3
3.3kΩ VR2
2
Ir3
R2
1.5kΩ VR3
1
Calculated
Measured
RT
IT
VR1
VR2
VR3
IR1
IR2
IR3
Fig 1.
2. Set E = 10V. Measure the values of VR1, VR2 and VR3 and enter in the table. Add up V2
and V3. Comment on your results.
3. Using the current measurement technique of Lab # 3, find the measured currents in
branch 1 (I1), and branch 2 (I2). Add I and I2 together, this sum should equal IT. Now
measure the total circuit current using the method of Lab 2 (break the circuit at point A
and insert an ammeter). Comment on your results. Enter these currents in the table.
Part D
Procedure:
4. Lessons of Lab 3, 4 and Part A of this lab can be applied to more complex series-parallel
circuit. The trick is to recognize simple series and parallel parts in the complex.
Combination circuit and then apply series circuit rules to the series parts and parallel
circuit rules to parallel parts.
5. Enter the values from the Pre-Lab for this circuit in Table 4 on the next page.
6
It 18
R1
1.5kΩ
V1
10 V
15
Ir2
A
Ir3
R2
R3
3.3kΩ 8.2kΩ
Jumper for fault simulation
when required
16
17
B
R4
1.5kΩ
Ir4 = It
Fig. 2
Calculated
Table 4:Measured
Simulated Fault
RT
IT
IR1
IR2
IR3
IR4
VR1
VR2
VR3
VR4
6. Measure the voltage drop on each of the resistors and record in your table.
7. Measure the current into the parallel loop by dividing V1 by R1. Repeat for the current
out of the loop (by dividing VR4 by R4). Enter in the table.
8. Measure the branch currents in the parallel branches (IR2, IR3) using the indirect
methods. Record in your table.
9. Add up V1, V2 and V4, also V1, V3 and V4.
V1 + V2 +V4 =
V1+V3+V4 =
Comment on your results.
10. Add IR2 and IR3. Compare with IT (or IR1 or IR4). Comment on your results.
11. Introduce a short circuit fault by connecting a jumper between points A and B as shown
in the circuit diagram Figure 2.
12. Measure RT, IT, IR1, IR2, IR3, IR4, VR1, VR2, VR3 and VR4 and enter in your results in the
table.
13. Based on your simulated fault measurement values, state some basic facts about short
circuit faults in series – parallel combination circuits.
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Questions and Assignments:
1. For E = 10V, R1=10K, R2=18K, R3=22K, Calculate RT, IT, VR1, VR2 and VR3. For a
series circuit, draw the circuit diagram. Show current direction and label all voltage
drops with proper polarities. Show each step on his calculations.
2. For the circuit shown, there is a break between resistors R2 and R1 as shown.
(a) What is the voltage across R2.
(b) What is the total circuit current.
(c) If the voltmeter is connected as shown, what would the voltmeter read?
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5
R1
6
R2
V2
25 V
8
V
R3
7
3. For E=25V, R1=10K, R2=18K, R3=22K, Calculate RT, IT, I1, I2, I3, VR1, VR2 and VR3 for
a parallel circuit. Draw the circuit diagram, show all current directions, label all
voltage drops with correct polarities clearly marked. Show each step of your
calculations.
4. Why was it not possible to measure the current using the indirect method when
measuring the total circuit current in part A, step 3?
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