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Due date:
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ECE 2006 LABORATORY 6
EQUIPMENT EQUIVALENT CIRCUITS
Objectives
The learning objectives for this laboratory are to give the student the ability to:
 determine the input resistance of the oscilloscope.
 determine the input resistance of the oscilloscope 10x probe.
 determine the input resistance of the digital voltmeter.
 determine the output resistance of a function generator.
 use PSPICE to determine a circuit's Thevenin equivalent.
References D. E. Johnson, J. R. Johnson, J. L. Hilburn, and P. D. Scott, Electrical
Circuit Analysis. 3rd Edition, Prentice-Hall, 1997.
Background
Figures. Each Figure must have a descriptive title and a number. Units must be included
for all numerical values. Figures must be neat and easy to read and understand.
Data. Data is to be taken in ink. It must be clear as to what the data refers to. Do not
forget units.
Sample calculations. Sample calculations are used to demonstrate how results were
obtained. Label each sample calculation so that it is clear as to what it refers to. Each
sample calculation should include a symbol equation and a set of numerical values, a
result, and units, such as
R = V/l
= 10 volts / 2 amps = 5 ohms
Equipment
Oscilloscope
DC power supply
Digital multimeter
Function generator
Resistors
PC with PSPICE.
Procedure
1.
Measure the internal resistance of the oscilloscope.
1.1
1.2
Connect the circuit in Figure 1 using the oscilloscope channel 1 for Ri.
Set Rv to 0 . Set the oscilloscope channel 1 sensitivity to 1 volt/div. Adjust the
DC power supply to about 8 volts. Use the oscilloscope for this measurement.
Record this voltage, Vps, on the data sheet.
1.3
Select a nominal 10 M resistor for Rv. Record the voltage Vi on the data sheet.
Remove this resistor, Rv, from the circuit and measure its resistance using the
DMM. Record this resistance on the data sheet.
1.4
Calculate the internal resistance of the oscilloscope, Ros, and record on the data
sheet. Show this calculation.
2.1
Measure the internal resistance of the oscilloscope with 10x probe.
1.1
Connect the circuit in Figure 1 using the oscilloscope with a 10x probe on channel
1 for Ri.
2.2
Set Rv to 0 . Adjust the DC power supply to about 8 volts. Use the oscilloscope
for this measurement. Record this voltage, V ps, on the data sheet.
2.3
Select a nominal 10 M resistor for Rv. Record the voltage Vi on the data sheet.
Remove this resistor, Rv from the circuit and measure its resistance using the
DMM. Record this resistance on the data sheet.
2.4
Calculate the internal resistance of the oscilloscope and probe, Ros + Rp, and
record on the data sheet. Show this calculation.
2.5
Calculate the internal resistance of the probe, Rp, and record on the data sheet.
Show this calculation.
3.
Measure the internal resistance of the digital multimeter, DMM, when used as a
voltmeter.
3.1.
Connect the circuit in Figure 1 using the digital voltmeter for Ri.
3.2
Set Rv to 0. Adjust the DC power supply to about 16 volts. Use the digital
voltmeter for this measurement. Record this voltage, V ps, on the data sheet.
3.3
Select a nominal 10 MO resistor for Rv. Record the voltage Vi on the data sheet.
Remove this resistor, Rv, from the circuit and measure its resistance using the
DMM. Record this resistance on the data sheet.
3.4
Calculate the internal resistance of the digital voltmeter, Rdmm, and record on the
data sheet. Show this calculation.
4.
Measure the output resistance, Ro, of the function generator.
4.1
Connect the circuit in Figure 2. Use the DMM for the voltmeter, VM. Select the
sinusoidal waveform output on the function generator. Adjust the frequency to
50Hz.
4.2
Remove RL (open the circuit at RL) and adjust Vfg to 1.6 volts. Record Vfg on the
data sheet.
4.3
Connect RL. Select a resistor for RL (approximately 50 ) such that Vo is about
0.8 volts. Record Vo on the data sheet. Measure RL using the DMM and record on
the data sheet.
4.4
Calculate the output resistance, Ro, of the function generator and record on the
Data Sheet. Show this calculation.
5.
Use PSPICE to determine the Thevenin equivalent circuit for the circuit in Figure
3.
5.1
Write and run two PSPICE programs, one to calculate the open circuit voltage,
Voc, and one to calculate the short circuit current, Isc, for the circuit in Figure 3.
5.2
Print the above 2 output files. Add the label "=Voc" next to the open circuit
voltage. Add the label ''=Isc'' next to the short circuit current. Attach these output
files. Record Voc and Isc on the data sheet.
5.3
Calculate the Thevenin voltage, Vth, and the Thevenin resistance, Rth. Add these
values to Figure 4 and to the data sheet. Show your calculation.
5.4
Erase your files from the hard disk. You're welcome to keep your files on your
own floppy disk.
Conclusions
None
Figure 1. Input resistance measurement.
Figure 2. Output resistance measurement.
Figure 3. DC circuit
Figure 4. DC circuit Thevenin equivalent
Data Sheet
1. Oscilloscope input resistance.
Rv = 0 ,
Vps = ______V
Rv = ______,
Vi = ______V
Ros = Ri = ______
2. Oscilloscope with probe input resistance.
Rv = 0 ,
Vps = ______V
Rv = ______,
Vi = ______V
Ri = Ros + Rp = ______
Rp = ______
3. Digital voltmeter input resistance.
Rv = 0 ,
Vps = ______V
Rv = ______,
Vi = ______V
Rdmm = Ri = ______
4. Function generator output resistance.
RL = ______,
Vfg = ______V
RL = ______,
Vo = ______V
Ro = ______
5. Thevenin equivalent for Figure 3.
Voc = ______V
Isc = ______A
Vth = ______V
Sample Calculations
Oscilloscope's input resistance:
Ros = Ri=
Oscilloscope with 10X probe input resistance:
Ri = Ros + Rp =
1 0X probe resistance:
Rp= Ri - Ros=
Digital voltmeter's input resistance:
Rdmm = Rj =
Function generator's output resistance:
Ro =
Thevenin's equivalent source voltage and output resistance for Figures 3 and 4:
Vth =
Rth =