2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
New set of Lab experiments
with ELVIS II
Alexander Ganago
Jason Lee Sleight
University of Michigan
Ann Arbor
Lab 2
Introduction to Multisim
© 2009 Alexander Ganago
February 7, 2009
Page 1 of 4
Lab2_Intro_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Goals for Lab 2
Learn how to simulate circuits and obtain data such as output voltages with Multisim
In the pre-lab, simulate circuits with semiconductor diodes – the “ideal” diode, which
is called DIODE_VIRTUAL and one of the “real” diodes – 1N914
In the lab, build semiconductor diodes circuits with 1N914 on ELVIS prototyping
board and take data with ELVIS test/measurement instruments
In the post-lab, compare the data you obtained for semiconductor diodes circuits in
pre-lab simulations and in the lab; draw conclusions on the accuracy of simulations
Learn about the Wheatstone bridge circuit and its applications in DC and AC
measurements
In the pre-lab, simulate balanced and unbalanced Wheatstone bridge circuits with DC
and AC sources
In the lab, build balanced and unbalanced Wheatstone bridge circuits with DC and AC
sources and take data with ELVIS test/measurement instruments
In the post-lab, compare the data you obtained on balanced and unbalanced
Wheatstone bridge circuits in the pre-lab and in the lab; draw conclusions on the
accuracy of simulations
In the lab, explore [for extra credit] various unbalanced Wheatstone bridge circuits
In the post-lab, explain [for extra credit] the data you obtained on various unbalanced
Wheatstone bridge circuits explored in the lab.
© 2009 Alexander Ganago
February 7, 2009
Page 2 of 4
Lab2_Intro_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Introduction
In this Lab, you will start working with Multisim – a powerful and user-friendly software
package for circuit simulation and data analysis, which is fully integrated with ELVIS II.
As soon as you learn new theory, you can:
1. Start using the new concepts to simulate a circuit with Multisim, and compare
results of simulations with the results you can obtain with other tools for circuit
analysis.
2. Build the same circuit on your ELVIS II prototyping board, collect data from
your circuit, and compare your real-world data with the results of your
simulations.
This integrated approach to learning new material helps you to develop intuition along
with mastering hands-on skills and problem-solving strategies. Along with deeper
understanding of circuit theory, you will practice circuit design and troubleshooting
valuable for your future careers.
Note that you can simulate your circuit using an “ideal” component such as “ideal diode”
that behaves exactly as the theoretical model predicts – or you can take advantage of the
database integrated in Multisim and model your circuit with a “real” diode whose
characteristics are provided by its manufacturer. Comparison between the results of such
simulations can provide you with a valuable insight into the accuracy of theoretical
model as well as guidance in choosing specific types of components for your particular
application. Running several simulations with various types of diodes will probably save
you time and money in building better circuits for your projects.
In this Lab 2, we will revisit the concept of non-ohmic voltage-current dependence in a
semiconductor diode and reinforce it with two types of simulations – for the “ideal”
diode, which is called DIODE_VIRTUAL and one of the “real” diodes – 1N914; in your
experiments with ELVIS II prototyping board you will also build a circuit with 1N914.
Secondly, we will explore the Wheatstone bridge – a very useful circuit for measurement
and control with resistive sensors.
© 2009 Alexander Ganago
February 7, 2009
Page 3 of 4
Lab2_Intro_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
As seen from the diagrams, the Wheatstone bridge is simply a pair of voltage dividers,
thus its output voltage is easy to calculate:
⎛ R4 ⎞
⎜⎝ R ⎟⎠
R4
1
4
V1 = VS ⋅
= VS ⋅
= VS ⋅
R1 + R4
⎛ R1 ⎞ ⎛ R4 ⎞
⎛ R1 ⎞
+
⎜⎝ R ⎟⎠ ⎜⎝ R ⎟⎠
⎜⎝ R ⎟⎠ + 1
4
4
4
⎛ R3 ⎞
⎜⎝ R ⎟⎠
R3
1
3
V2 = VS ⋅
= VS ⋅
= VS ⋅
R2 + R3
⎛ R2 ⎞ ⎛ R3 ⎞
⎛ R2 ⎞
⎜⎝ R ⎟⎠ + ⎜⎝ R ⎟⎠
⎜⎝ R ⎟⎠ + 1
3
3
3
VOUT
⎛
⎞
⎛ R2 ⎞ ⎛ R1 ⎞
⎜
⎟
⎜⎝ R ⎟⎠ − ⎜⎝ R ⎟⎠
1
1
3
4
⎟ = VS ⋅
= V1 − V2 = VS ⋅ ⎜
−
⎛ R2 ⎞
⎜ ⎛ R1 ⎞
⎟
⎡⎛ R1 ⎞ ⎤ ⎡ ⎛ R2 ⎞ ⎤
⎜ ⎜ R ⎟ + 1 ⎜ R ⎟ + 1⎟
⎢⎜ ⎟ + 1⎥ ⋅ ⎢ ⎜ ⎟ + 1⎥
⎝ 3⎠
⎝⎝ 4⎠
⎠
⎣⎝ R4 ⎠ ⎦ ⎣ ⎝ R3 ⎠ ⎦
Note that the output voltage is zero, regardless of the source voltage, if the ratios of
R
R
resistances in two voltage dividers equal each other 2 = 1 . This is called a balanced
R3 R4
Wheatstone bridge.
Suppose that R1 is variable while other 3 resistors are constant. Then the output voltage is
R
R
R
R
R
R
positive if 1 < 2 ; the output is negative if 1 > 2 , and vanishes if 1 = 2 . The
R4 R3
R4 R3
R4 R3
Wheatstone bridge whose output signal is non-zero, is called unbalanced.
Note that the output voltage of the Wheatstone bridge circuit is directly proportional to
the source voltage. If the source is DC (with voltage independent of time), such as a
battery, the output is DC voltage as well. If the source is AC (time-dependent voltage),
for example, sinusoidal voltage VS = VS,max ⋅ sin(2π ⋅ f ⋅ t) with the peak value VS,max , at the
frequency f Hz, the bridge output voltage will also be sinusoidal, at the same frequency.
It is easier to detect small output signals of an unbalanced bridge using sinusoidal
voltages instead of DC, to separate useful signals from noise by filtering, etc.
© 2009 Alexander Ganago
February 7, 2009
Page 4 of 4
Lab2_Intro_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Pre-Lab Work
The assignments you have to bring to the lab are typed in bold font.
Part 1: I-V Characteristics of a Diode
Section 1.1: Diode Characteristics
In Pre-Lab Part 1, you will simulate 2 circuits with semiconductor diodes – one with an
“ideal” diode, which is called DIODE_VIRTUAL, the other with a diode, which has the
characteristics of 1N914. You will compare the results of these two simulations side-by
side with each other and with real data that you will receive in the lab.
□ Open NI Multisim (may be named NI Circuit Design Suite).
□ Click the “Place Diode” key to open the diode selection window.
□ In the diode selection window, click on the Diodes_Virtual family, then place a
DIODE_VIRTUAL onto your circuit.
□ Select the Diode family and place a 1N914 diode onto your circuit.
□ Click the add I-V Analysis and place the I-V Analyzer tool into the circuit. Do this
again to add another I-V Analyzer.
□ Add wires to create the following circuit:
© 2009 Alexander Ganago
February 7, 2009
Page 1 of 5
Lab2_preLab_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
□ Run the simulation by clicking the green triangle button. You should allow it to run for
a few seconds in order to get an accurate picture of the I-V characteristics. Stop the
simulation.
□ Open the Grapher tool to view the simulation results (found in the View menu). You
can switch between the two I-V graphs by clicking the respective tabs.
NOTE: if you make a mistake and have to run the simulation again, you will have more
than two tabs. The most resent results will be displayed on the furthest right. You can
delete the old simulation results by doing Clear Pages (found in the Edit menu) and then
selecting the graphs you no longer want.
□ Export the results of each graph to Excel (found in Tools menu). If the option is
grayed out, then click on the graph and try again.
#1. Print out the voltage-current plot for DIODE_VIRTUAL.
#2. Print out the voltage-current plot for 1N914.
#3. Create a plot that shows the power consumption by each of the diode (as
function of voltage applied to the diode) to turn in as part of your Pre-Lab.
#4. Write a brief comparison between the results of 2 simulations. Explain which
one you consider more realistic and why.
© 2009 Alexander Ganago
February 7, 2009
Page 2 of 5
Lab2_preLab_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Part 2: Wheatstone Bridge
In Pre-Lab Part 2, you will simulate balanced and unbalanced Wheatstone bridge circuits.
You will start with the balanced circuit where R1=R2=100 Ω and R3=R4=200 Ω; then
you will change R4 to 205 Ω and 210 Ω in order to simulate the signals from an
unbalanced circuit. You will run these simulations twice – for DC and AC sources.
Section 2.1: Wheatstone Bridge at DC
□ Create a new circuit by clicking File..New..NI ELVIS II Schematic.
□ Create the following circuit:
The red wire is connected to the VPS’s Supply+ terminal, the black wire is connected to
the VPS’s Ground terminal, the yellow wire is connected to the DMM’s V terminal, and
the green wire is connected to the DMM’s COM terminal.
□ Double click on the VPS and DMM icons to bring up their respective VIs.
□ On the VPS VI, set SUPPLY+ to be 6V and ensure the device is Multisim.
© 2009 Alexander Ganago
February 7, 2009
Page 3 of 5
Lab2_preLab_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
□ On the DMM VI, ensure the device is Multisim and click the green V to set the DMM
to DC voltage mode.
□ Run the simulation.
#5. Record the value of the output voltage across the balanced bridge measured with
the DMM.
#6. Change R4 to be 205Ω. Rerun the simulation and record the new value across
the bridge.
#7. Change R4 to be 210Ω. Rerun the simulation and record the new value across
the bridge.
#8. Save you circuit. You will need the file for the in-lab, so make sure you bring it
with you.
#9. Calculate the output voltage values expected for #6 and #7. Briefly discuss the
agreement/disagreement between the results of your theoretical calculations
and the results of your circuit simulations.
Unclear whether students have to sweep the
source voltage (as sample data show) or just
use one value (then only a part of sample
data is needed).
Also, is it correct to assume that answer to
#8 is simply the diagram shown on page 3
of this file?
© 2009 Alexander Ganago
February 7, 2009
Page 4 of 5
Lab2_preLab_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Section 2.2: Wheatstone Bridge at AC
□ Repeat section 2.1, this time using the following circuit (create a new file, so that you
have two different files to bring along to lab. One for DC and one for AC):
The red wire is connected to the FGEN pin and OSCOPE CH0+, the black wire is
GROUND and OSCOPE CH0-, the yellow wire is OSCOPE CH1+ and the green wire is
OSCOPE CH1-.
#10. Record the value of the output voltage across the balanced bridge measured
with the oscilloscope.
#11. Change R4 to be 205Ω. Rerun the simulation and record the new value across
the bridge.
#12. Change R4 to be 210Ω. Rerun the simulation and record the new value across
the bridge.
#13. Save you circuit. You will need the file for the in-lab, so make sure you bring it
with you.
#14. Use the results of your calculations in #9 above. Explain whether the output
voltages for #6 and #7 should equal those for #11 and #12. Briefly discuss the
agreement/disagreement between the results of your theoretical calculations
and the results of your AC circuit simulations.
© 2009 Alexander Ganago
February 7, 2009
Page 5 of 5
Lab2_preLab_v3_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
In-Lab Work
Part 1: I-V Characteristics of a Diode
Section 1.1: Diode Characteristics
□ Turn on the Elvis II
□ Wire a 1N914 diode to the DMM/Impedance Analyzer (terminal strips 29 and 30).
□ Power on the PB.
□ Open the ELVISmx Instrument launcher and run the Two-Wire Current-Voltage
Analyzer
□ Set the settings as follows:
□ Run the VI.
□ Log the data and create a printout of the plot.
□ Power off the PB.
© 2009 Alexander Ganago
Page 1 of 6
Lab2_inLab_v2_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Section 2: Wheatstone Bridge
Section 2.1: Measuring Resistance
□ Get two 100Ω, two 200Ω, and two 10Ω resistors.
□ Using banana cables with alligator clips, connect one of the 100Ω resistors to the
DMM ports on the left hand side of the Elvis II. One end of the resistor should go to
the COM port and the other to the Ω port directly above the COM port.
□ On the ELVISmx Instrument Launcher, run the DMM.
□ Put the DMM in ohmmeter mode by clicking the green Ω symbol.
□ Run the VI.
□ Record the actual resistance of the resistor in the table below. Repeat resistance
measurements for the other five resistors. Make sure you remember which resistor is
which value!
Nominal Value (Ω)
Actual Resistance (Ω)
100
100
200
200
10
10
□ Stop the DMM VI.
© 2009 Alexander Ganago
Page 2 of 6
Lab2_inLab_v2_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Section 2.2: Wheatstone Bridge at DC
□ Open Multisim and load your pre-lab circuit of the 5Ω unbalanced Wheatstone bridge
which uses the VPS and DMM. If you circuit still has the 10Ω unbalancing or is
already balanced then remove/add those resistances to your model before continuing.
□ Build your circuit on the PB. For the DMM connections, you must use banana clips
with alligator clips to connect to the DMM ports on the Elvis (like you did for resistance
measurements). Use the two 10Ω resistors to create the 5Ω resistor.
□ Record which resistor is in which location of your Wheatstone bridge. You will need
this information for the post-lab.
□ Power on the PB.
□ In Multisim, double click the VPS symbol and then the DMM symbol to open up the
respective VIs.
□ On the DMM, click the green V to put the DMM in DC voltage mode. Set the VI to
collect real data by changing the device to be NI ELVIS II.
□ Run the VI.
□ On the VPS, again set the device to NI ELVIS II and also set the following settings:
This will give you 7.5 seconds to record a data point. If you would like longer, then
increase the step interval.
□ On the VPS, click the Sweep button to start the VI. Record the DMM voltages in the
table on the next page.
□ Repeat the measurements for a 10Ω unbalance and a balanced bridge.
□ Power off the PB.
© 2009 Alexander Ganago
Page 3 of 6
Lab2_inLab_v2_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
VIN (V)
VOUT (mV) 5Ω VOUT (mV) 10Ω
VOUT (mV) balanced
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
5.50
6.00
© 2009 Alexander Ganago
Page 4 of 6
Lab2_inLab_v2_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Section 2.3: Wheatstone Bridge at AC
□ Open Multisim and load your pre-lab circuit of the 5Ω unbalanced Wheatstone bridge
which uses the FGEN and OSCOPE. If you circuit still has the 10Ω unbalancing or is
already balanced then remove/add those resistances to your model before continuing.
□ Build your circuit on the PB. Make sure you remember which resistor has which actual
resistance value (measured in part 2.1)! Use the two 10Ω resistors to create the 5Ω
resistor.
□ Power on the PB.
□ Double click on the FGEN and then the OSCOPE icons to open the VIs.
□ On the FGEN VI, set the device to Multisim and set the following settings:
□ On the OSCOPE VI, set the device to Multisim.
□ Run the simulation.
□ Adjust the Volts/div and Time/div settings on the OSCOPE to view the signals.
□ Once you have the data, stop the simulation.
□ On the FGEN VI, set the device to NI ELVIS II.
□ Run the FGEN VI.
□ On the OSCOPE VI, set the device to NI ELVIS II. Also change the Channel 0 and 1
sources to AI 0 and 1 respectively.
□ Run the OSCOPE VI.
□ Check the Simulated Data and Real Data boxes so that both the simulation and real
data are simultaneously displayed on the plot.
□ Log the data and create a printout of the plot.
□ Repeat this section with both the 10Ω unbalanced and balanced bridge circuits. Make
sure you change the resistor values in the simulation as well.
© 2009 Alexander Ganago
Page 5 of 6
Lab2_inLab_v2_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Section 3: Explorations, for extra credit
This is the end of the required lab. If you are not going to
continue with the explorations, power off the PB and ELVIS II
and clean up your workstation.
Section 3.1: Opposite leg unbalanced
□ Change your circuit so that the offset is on the other leg of the bridge (i.e. in series with
the other 200Ω resistor).
□ Redo section 2.3, however leave the simulation circuit unchanged (so your unbalances
are in series with different resistors). Still change the simulation from 5Ω to 10Ω to
balanced as directed.
Section 3.2: Top half unbalanced
□ Change your circuit so that the offset is on the top half of the bridge (i.e. in series with
a 100Ω resistor).
□ Redo section 2.3, however leave the simulation circuit unchanged (so your unbalances
are in series with different resistors). Still change the simulation from 5Ω to 10Ω to
balanced as directed.
This is the end of the lab. Power off the PB and ELVIS II and
clean up your workstation.
© 2009 Alexander Ganago
Page 6 of 6
Lab2_inLab_v2_AG
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Post-Lab
1.
Compare your In-Lab Part 1 data with your Pre-Lab results in #1, #2. Briefly discuss the
agreement and/or disagreement between both simulations and your real data.
2.
Typically, when students do Section 2.2 measurements on the balanced Wheatstone
bridge in the lab, they obtain non-zero output voltages. Explain why.
3.
Use the actual resistances measured in the lab and calculate the output voltages expected
for 6 V DC input in the following circuits:
-
the balanced Wheatstone bridge
-
the bridge with R4 = 205 Ω
-
the bridge with R4 = 210 Ω.
Compare the results of your calculations with your lab data obtained in Section 2.2. .
Briefly discuss the agreement and/or disagreement between them.
4.
When students do experiments in Section 2.3, they usually obtain two pairs (input and
output) of traces on each oscilloscope screenshot: one that belongs to pre-lab simulations
and the other that shows the lab data.
The input measured with the oscilloscope in the lab differs from the expected 6 V p-p set
on the function generator because the total resistance of the bridge circuit is small and
loads the function generator’s output. The output is proportional to the input, and it also
depends on the actual (not nominal) resistances in the bridge circuit. These two causes of
discrepancies between simulation and real data can be taken into account.
Redo your pre-lab simulation for the bridge with R4 = 210 Ω making both corrections:
(1) Instead of the 6 V p-p input, use the actual V p-p of the input signal that you
measured with oscilloscope in the lab, and
(2) Instead of nominal resistances, use the actual ones measured in the lab.
Compare the results of new simulation with your lab data and comment on whether the
agreement improved.
This is the end of required Post-Lab.
Optional (extra credit) assignments are on the next page.
© 2009 Alexander Ganago
February 7, 2009
Page 1 of 2
2009 ELVIS Lab Book
Lab 2: Introduction to Multisim
Post-Lab
Optional (extra credit) assignments
5.
Explain the difference of output voltages expected in the Wheatstone bridge circuits:
A. R1 = R2 = 100 Ω,
R3= 200 Ω,
R4 = 210 Ω
B. R1 = R2 = 100 Ω,
R3= 210 Ω,
R4 = 200 Ω
Confirm your explanation with analytic calculations and/or Multisim simulations.
6.
Compare the result of #5 above with your lab data in Section 3.1.
7.
Explain the difference of output voltages expected in the Wheatstone bridge circuits:
C. R1 = R2 = 100 Ω,
D. R1 = 110 Ω,
R3= 200 Ω,
R2 = 100 Ω,
R4 = 210 Ω
R3 = R4 = 200 Ω
Confirm your explanation with analytic calculations and/or Multisim simulations.
8.
Compare the result of #7 above with your lab data in Section 3.2.
9.
When your Wheatstone bridge (which was originally balanced) is unbalanced by adding
10 Ω to resistance R4=200 Ω, the output voltage changes from 0 to V4.
When your Wheatstone bridge (which was originally balanced) is unbalanced by adding
10 Ω to resistance R1=100 Ω, the output voltage changes from 0 to V1.
Why does V1 not equal V4?
© 2009 Alexander Ganago
February 7, 2009
Page 2 of 2