Physics 301
Basic Circuits with Multisim
P. C. Womble
Purpose: This exercise will introduce the student to the Multisim circuit simulation
software. Simple circuits will be simulated and then replicated on the NI-ELVIS.
Introduction: The main Multisim screen is shown in Figure 1. Multisim is a graphical
user interface for circuit design. Furthermore, Multisim uses the SPICE circuit
simulation code to simulate voltages and currents within a circuit.
Power Supplies
Components:
Resistors,
capacitors, etc.
Instruments:
Meters,
oscilloscopes,
etc.
Figure 1. Screen layout for Multisim.
Each component is selected and can be positioned on the grid points on the main form. A
drawing tool can be used to connect the components. Figure 2 shows a connected circuit.
A more detailed description can be found in the “Elvis User Guide” PDF file.
Figure 2. Schematic drawn in Multisim
Running SPICE: Virtual instruments such as voltmeters, ammeters, and oscilloscopes
can also be simulated. They are connected in a manner similar to real instruments. For
example, an ammeter is connected in series to a component and a voltmeter is connected
in parallel to a component.
One “quirk” of the program is that a ground connection must be provided (see Figure 2).
A simulation is started by going to the menu and selecting “Simulation” and then “Run”.
Alternative, one can press “F5”.
By default, a simulation starts at time, t=0, and runs for 1030 seconds. These limits can
be changed under the “Simulation” menu and selecting “Interactive Simulation Settings”.
Also the time step can be changed, thus speeding up or slowing down the simulation.
Circuit 1: R1=R2=R3=3 k, R4=R5=20 k, U1=U2=U4=ammeters, U3=U5=voltmeters, V1=15
V
Exercise 1:
1. Using Kirchoff’s loop rules and the rule of equivalent resistors, calculate the
values of the indicators U1 through U5 for Circuit 1. Show all work on the
worksheet and place your values in the table therein.
2. Set up Circuit 1 in the Multsim software. Allow the simulation to run through
several simulated seconds and note the values
3. Set up Circuit 1 on the NI-ELVIS. Use the Fluke 115 multimeter to measure the
current at the positions of U1, U2, and U4.
a. A 15 volt power supply is available from the NI ELVIS.
Circuit 2: C1= 10 uF, R1=10 k, XSC1=XSC2=Oscilloscope, U1=ammeter, V1= 10 V, pulsed, 1
ns duration, period of 1 s.
Exercise 2:
1. Calculate the RC time constant of Circuit 2.
2. Set up Circuit 2 in Multisim.
3. Use the “Grapher” function under the “View” menu to graph the voltage on
channel A of oscilloscopes XSC1 and XSC2 for the first 0.5 seconds of the
simulation.
4. Fill out questions 1-4 on Circuit 2 on the laboratory worksheet before continuing.
5. Open “The Arbitrary Wave Form Generator” on the NI-ELVIS menu. Load the
“Circuit2.wdt” file into the form at DAC0. The “Circuit2.wdt” is file that
contains a waveform which will be looped. Set the mode to the “loop” symbol.
Press “Play next to DAC0.
6. Wire Circuit 2 on the NI-ELVIS. The “+” side of voltage source V1 will be
DAC0. The “-“ side will attached to either “ground” connections on the left side.
a. You may have some difficulty finding a “10 uF” capacitor. Use any
capacitor on the order of 10 uF. Be sure to note the exact values of your
resistor/capacitors on the worksheet.
7. Use the board connections for Channel A (“Chan A +” and “Chan A –“ ) as your
oscilloscope leads. Connect them in parallel to the position XSC1. Measure the
time it takes the waveform to get to 68% of its final value. Re-position the
connectors to the XSC2 position and measure the time it takes to get to 68% of its
final value. Record these on the worksheet.
8. Calculate the RC time constant for your resistor/capacitor combination.
9. Fill out the other questions in the worksheet under Circuit 2.
Circuit 3:
1. Vary the resistor and the capacitor by a factor of 10 larger and a factor of time
smaller in the Multisim calculation. Describe in the worksheet how the
waveforms for XSC1 and XSC2 have changed by this variation.
Circuit 4:
1. Replace R1 with a 10 mH inductor in the Multisim calculation. Describe the
changes that you observe at XSC1 and XSC2 in the worksheet.
Finishing Up:
Return all components to where you found them. Turn off the NI-Elvis. Hand in work
sheet next week.