EE 3010 - Laboratory
Experiment 2
Experiment 2: Simulation of DC Resistive Circuits
Objectives:
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Simulate DC Resistive circuits using Orcad PSpice Software.
Verify experimental and theoretically calculated results for a given resistive network.
Observe balanced and unbalanced Wheatstone bridge circuit.
Investigate voltmeter loading effects.
Pre Lab:
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Bring a 3.5” diskette to lab. You will need it to save your files.
Read and understand Appendix D in the text.
Do problem 2.18. Determine the current through the 12-Ω resistor, current passing through the
25-Ω resistor, and the voltage drop across the 30-Ω resistor. Bring your detailed solution to lab.
Enter these values on Table 1 of the Data Sheet.
Transfer your measured resistor values from Experiment 1 to Table 2 of the Data Sheet
Transfer your measured voltage and current values from Experiment 1 for voltage source and
resistors to Table 3 of the Data Sheet.
Using your measured resistor values from Experiment 1, calculate theoretical voltages and
currents for the circuit described by Figure 1. Enter these values on Table 3 of the Data Sheet.
Components Used:
Orcad Lite 9.2 Software for the PC supplied on one of the CDs with the text.
Part A: Introduction to Capture/PSpice
Procedure:
1. Using the computer in the laboratory, start the Orcad software and follow the example described
in Section D.1 of the text. Ask your Lab Instructor for help if necessary.
2. Save the completed circuit as a file to your diskette. This circuit can be printed to the network
printer. You may also copy the circuit and paste it in a word document as a circuit schematic and
include with your lab report.
3. Open the sample circuit provided in lab for Problem 2.18 of the text and record the current value
through the 12 Ω resistor on Table 1 of the Data Sheet.
4. Click on the current (voltage) icon to display the element currents (node voltages). Record values
on Table 1 of the Data Sheet. (You will need to calculate the difference between two node
voltages to determine the voltage across the 30 Ω resistor.)
Conclusions:
1. Does the simulation provide accurate values when compared with calculated values? Explain.
Page 1 of 4
EE 3010 - Laboratory
Experiment 2
Part B: Parallel and Series Circuit
Procedure:
1. Figure 1 is the schematic for the final circuit constructed in Experiment 1. As a prelab activity,
you should have transferred measured values for R1, R2, R3, and R4 to Table 2 of the Data Sheet.
You should have also transferred measured and calculated values for voltages and currents to
Table 3 of the Data Sheet.
2. Construct a schematic of the circuit shown in Figure 1 using Capture. Assign the measured values
from experiment 1 to the components of this schematic. Change the values by double clicking on
the component and editing the value cell. Components may be rotated or flipped by right clicking
on a component and using the pop-up menu.
Figure 1
3. Run the bias point simulation and record the values for current through and voltage across each
component in Table 3 of the Data Sheet.
Conclusions:
1. Does the simulation provide accurate values when compared with both measured values and
calculated values? Explain.
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EE 3010 - Laboratory
Experiment 2
Part C: Wheatstone bridge
Procedure:
1.
Construct a schematic of the circuit shown in Figure 2 using Capture. Assign various values to
R1, R2, R3 and R4 according to the Table 4 in the Data Sheet. Change the values by double
clicking on the component and editing the value cell.
2.
Figure 2
3.
Record the values for current through XY for all these cases.
Conclusions:
1.
Comment on the effect of different resistance values on the current across the branch XY.
Part D: Instrument Loading
Voltmeters have very high resistances that typically exceed 1 MΩ. If the circuit uses relatively low
resistance components (say, less than 10KΩ) the resistance of the voltmeter has a negligible effect on
the circuit. However, this is not always the case. When a voltmeter changes the voltages in the
circuit being measured, we say that the meter “loads” the circuit. In Part C we investigate loading
caused by the internal resistance of a voltmeter and its effect on a circuit.
Procedure:
1. Construct the circuits shown below using Orcad Capture. Run a PSpice Bias Point Analysis and
verify that the node voltages are the same in both circuits. Record the voltages in Table 5 of the
data sheet.
2. Now suppose that we have these circuits actually set up in the lab and we want to measure the
voltages at nodes A and B. Voltmeters have finite resistances. In other words, they draw some
current from the circuit that they are measuring. A model for a typical voltmeter is a 1 MΩ
resistance. Add 1 MΩ resistors from points A and B to ground in each circuit to model
voltmeters used to measure the node voltages. Simulate the circuit and record the node voltages
in Table 4.
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EE 3010 - Laboratory
Experiment 2
Conclusions:
2. Comment on the effect that the resistance of the voltmeter has on the voltages. When should we
be suspicious that a voltmeter might load a circuit being measured? When is it likely to not be a
problem?
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EE 3010 - Laboratory
Experiment 2
Data Sheet
Table 1: Problem 2.18
Calculated
(Prelab)
Table 3: Parallel and Series Circuit
Simulation
I12
Measured
I25
Calculated
(Prelab)
Simulation
(EWB)
Vs
V30
Is
V470
I470
Table 2: Measured Resistor Values
Nominal Value
(Ohms)
V1000
Measured Value
(From Experiment 1)
I1000
V1500
R1
I1500
R2
V220
R3
I220
R4
Table 4: Wheatstone Bridge
R1
100Ω
100Ω
100 Ω
150Ω
R2
110Ω
110 Ω
110Ω
100 Ω
R3
200Ω
200Ω
100Ω
75Ω
R4
220Ω
400 Ω
220Ω
50Ω
IXY
Table 5: Instrument Loading
VA
VB
Original Circuits
Circuits with “voltmeters” added
Your Name_____________________________
Partner Name___________________________
Lab Instructor___________________________
Page 5 of 4
Date______________