Introduction to Multisim

Prepared by: Mohamad Eid,

Updated by: David Modisette

Fall 2020

The purpose of this document is to introduce the many features of Multisim. Begin by first

opening up Multisim. For Windows users the default location can be found by clicking: Start

->All Programs -> National Instruments -> Circuit Design Suite ## -> Multisim [Version

Number] Be sure to note the version number you are using in your report in the Equipment

section. You should see a screen similar to Figure 1 below. This is called as a “Capture and

Simulate” environment because you “Capture” your schematic by drawing it in Multisim and

then you “Simulate” it.

Figure 1 shows the different parts of the Multisim workspace. Note that the location of the

toolbars on your Multisim window may be different slightly.

Figure 1. The most important components in the Multisim workspace

If you don’t see the toolbars shown above, Left-click on the View tool item and go to Toolbars.

Make sure the toolbars shown in figure 1 are checked as shown in figure 2.

Figure 2. Viewing the toolbars

Please familiarize yourselves with the location of each toolbar as it appears in your Multisim

window. We will be repeatedly referring to the toolbars throughout this document (using the

color codes from Figure 1, example: the Virtual Toolbar).

Example 1: Simple DC Analysis in Multisim

Let’s construct the simple circuit shown in figure 4.

Figure 3. A simple series circuit constructed in MultSim

Constructing this circuit in Multisim is easy:

1. Left-Click on the Power Source Family in the Virtual Toolbar.

2. The Power Source Components will pop up.

3. Left-Click on the DC Power Source icon and drag a battery onto the circuit workspace.

Figure 5 shows the result.

Figure 4. A DC power source in Multisim

If you want to change the value of the power source, Double-click the battery. This opens up

the Power Sources dialog box shown below.

Figure 5. Power Sources Dialog box. Use this to change the value of the battery voltage.

Let’s add the resistor and the potentiometer. Left-Click the Basic Components Family in the

Virtual Toolbar.

5. The Basic Components will pop up.

6. Left-Click on the Virtual Resistor tool and drag a resistor onto the workspace. As in the case

of the battery, you can Double-click the resistor to change component values.

7. Lets complete the circuit by placing the potentiometer. Left-Click on the Potentiometer Tool

and drag a potentiometer onto the workspace. You can increase (decrease) the resistance on the

potentiometer by pressing the “A” (Shift+A) key. Note: The increase and decrease refers to the

resistance between the middle leg and the bottom leg of the potentiometer. Double-click the

potentiometer to change the total resistance of the potentiometer and the increment or

decrement in the resistor value.

Figure 7 shows the circuit components placed on your workspace. The “50%” next to the

potentiometer means that the resistance between the middle leg and bottom leg is 50% of 1 kΩ:

500 Ω. If you press A, you will notice that resistance will increase by 5% (the resistance

between the middle leg and the top leg will decrease by 5%). Again, Double-click the

potentiometer to change the increment percentage.

Figure 6. The circuit components are in place.

8. The final component to place is the ground. You cannot simulate the circuit without a

ground. The reason for this is SPICE (the underlying simulation engine) uses nodal analysis to

solve circuits. The first step in nodal analysis is to pick a ground node. It does not matter where

we ground the circuit, for consistency let’s pick the node at the negative terminal of the power

supply at the bottom of the circuit as ground. See Figure 5 where we can get the ground.

Left-click the Ground tool in the Power Source Components menu. Drag the ground to the

bottom of the circuit, the result is shown in figure 7. Circuit is ready for wiring

9. To wire the circuit, simply Left-click at the starting node, drag the wire to the ending node

and Left-click again. Figure 8 shows the results of wiring the 12 V source to the 1 kΩ resistor.

Note the curser is a dot in cross-hairs when wiring. Complete the wiring as shown in figure 8.

Make sure you connect to the wiper of the potentiometer.

Figure 7. The circuit is complete

Remark: To make debugging easier in larger circuits, it would be instructive to change the wire

colors. To do so, Left-click on the wire to select it and then Right-click to choose Wire color.

Figure 9 shows the result. You should try to stick to electronics wire color conventions. For

example: RED for power and BLACK for ground.

Figure 8. Wire Color Selected.

Before we can simulate the circuit, we need to add instruments so we can make measurements.

One of the neat things about Multisim is that it comes with a bunch of standard instruments.

These instruments are the same (except for the scope) as on your lab bench. Hence your

simulation environment is a step closer to your real lab environment.

Let’s measure the voltage drop across the potentiometer. This will make an interesting exercise

since you can see the voltage across the potentiometer change as you vary the potentiometer

resistance.

10. Left-click the Agilent Multimeter from the Instruments Toolbar and drag the multimeter

onto your workspace. Figure 10 shows the result.

Now, Double-click on the multimeter to open up the instrument’s front panel.

Figure 9. The Agilent 34401A Simulated Multimeter front panel

Notice how the simulated multimeter is the same as the one on your workbench! Left-click the

Power button to turn on the instrument. You will be measuring DC voltage, so Left-click the

DC V button on the instrument. Figure 10 shows what you should get.

All that is left is to wire the multimeter terminals. Complete the wiring as shown in figure 10.

Connect to the wires to the multimeter on the workspace. As you make the connections,

Multisim highlights the terminals on the frontpanel.

11. To simulate the circuit, Left-click the “Simulate” button in the Simulation Toolbar. Figure

10 shows the result.

One of the most powerful features of Multisim is its interactive nature. Change the resistance of

the potentiometer by moving the wiper position. Pressing “A” or Shift+A and note how the

multimeter readings change (you may need to wait a couple of seconds for the multimeter to

register the change). Change the potentiometer resistance all the way to 1 kΩ. (100%). What is

the output voltage? Does this agree with your intuition and circuit properties? Hint: Think about

what the voltage divider formula when R1 = R2.

Assignment:

Simulate the following circuits a) and b): Determine the Loop Currents and the Component

Voltages for each circuit.

The Loop Current or Mesh Current Method solves circuits by writing Kirchhoff's Voltage

Law for currents flowing in the loops of a circuit.

See: https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-dc-circuit-analysis/a/ee-mesh-current-method

This will allow you to calculate the currents flowing through each component and with Ohm’s

Law, V = I x R, (Voltage equals Current times Resistance) and knowing the currents, you can

the voltage on each component.

Short explanation of electrical circuit analysis

(For the students just beginning electrical studying)

There are two types of electrical charge. They are called Positive and Negative.

Electric Charge, or just charge, is the physical property of matter that causes it to experience a

force when placed near another electric charge. If the charges are alike, two positive or two

negative, then there is a force between them that forces them away from each other. If the

charges are opposite, a positive and a negative, then there is a force to draw then together.

This force is called the Electromotive Force, EMF, and it is measured in Volts so it is usual

to use the term Voltage synonymous with EMF.

Electric Current, or just current, is the flow (rate) of electric electrical charge.

If the EMF or Voltage is greater than the force holding the charge in place then the charge will

move or flow and produce a current. If the EMF or Voltage is not greater then there is Voltage

but no current (flow).

The impediment to the flow of charge is called Resistance since it resists the flow of the

charge.

The study of electricity concerns the electric charge and how it moves. Its movement is

determined by the relationship among three main characteristic of the electricity’s path:

Resistance, Voltage, and Current.

Ohm’s Law is the Voltage(V) = Current (I) times Resistance (R),

V = IxR => V/R = I => V/I = R

To determine one of these characteristics one must know the other two. When several

components are connected together to form the path or Circuit for the electrical charge to

move through, then Ohm’s law can be applied to each component to determine the voltage

across the component and/or the current through the component. There are two other laws used

to help determine the voltage and current across circuit components: Kirchhoff’s Voltage Law

and Kirchhoff’s Current Law.

Kirchhoff’s Voltage Law, KVL, states that if the voltages of the components that form a full

loop or circle in the circuit are added together then the sum must be zero. Another way to think

of this is: When I get back to where I started around the loop, I must be back to the same

voltage. If I go up 5 V then to get back where I started I must go down 5 V.

A more formal/mathematical expression of KVL is the sum of the Voltages, positive and

negative, around any closed loop in an electrical circuit is zero.

Kirchhoff’s Current Law, KCL states that charge cannot be stored at a junction between

electrical components. This means that if current flows into a junction it must flow out of the

junction. Now there may be more than one path into and out of a junction but all the current

flowing in must equal all the current flowing out. A more formal/mathematical expression of

the KCL is the sum of the positive and negative currents flowing into a node of an

electrical circuit must equal zero.

Now KVL and KCL are true only under a certain condition. Electrical waves move at or near

the speed of light. As a matter of fact, light is electromagnetic waves that our eyes can detect,

just as our ears detect the pressure waves in the air that is sound.

We can vary how quickly the wave changes from positive to negative and back to positive.

This is the frequency with which the wave changes. In electrical engineering we have agreed to

name the number of times this change or cycling from positive to negative and back to positive

that happen in 1 second the frequency of the wave. Now the frequency of the wave is in the

number of cycles in 1 second. If we divide the 1 second by the number of cycles we get the

time of 1 cycle called the Period. Knowing the time in one cycle and the speed of the wave in

distance/time, we can calculate the distance traveled by one cycle of the wave. This distance

is called the wavelength of that frequency.

Now for KVL and KCL to be valid, the components’, of the circuit, physical sizes must be

much smaller than the frequency’s, that is applied to the circuit, wavelength. Otherwise, the

components will act like radio antennas and allow energy to escape the circuit and be lost.

Another needed bit of information for this lab is:

Resistors impedance to the flow AC current is just its resistance, R.

A capacitor’s impedance to the flow of AC current is dependent on the frequency of the AC

current. The formula for the magnitude of the capacitor impedance is Xc = 1/(2 fC), where

Xc is called the reactance of the capacitor and is in Ohms, f is the frequency in

Hertz(cycles/sec), and C is the capacitance in Farrads.

For more explanations see:

Electric current: https://en.wikipedia.org/wiki/Electric_current

Electric resistance: https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

EMF (Voltage): https://en.wikipedia.org/wiki/Electromotive_force

Comments on doing the lab and report:

The lab report is to convey to others what was done, how it was done, what was expected, what

the results were, and how the results compare to what was expected. It is best if the report is

accurate, clear, concise and complete. It should be written such that another EE/CE student

could repeat exactly what you did and get exactly the results you obtained. Review the

Laboratory Report Format example and try to follow the format as closely as possible while

adapting it to particular experiment being done.

To inform the lab report reviewer what was done, the Procedure section of the report should

explicitly reference this procedure document by title and URL. If you deviate from the

instructions for some reason, this should be noted in the report. Describe the deviation and the

reason. Any information you feel should be restated to improve the understanding of the report

should also be included. An item that must always be included in the report is the schematic of

any circuit that is discussed or has measurements presented. This allows the reader to know

what and where a characteristic of the circuit is discussed or presented.

When doing simulations and measurements we need to know what value we expect the

measurements to be before doing the measurements. This allows us to confirm the experiment

was correctly configured, correctly performed, and correctly measured. If our results are

considerably different from expected, then there is at least one error somewhere and it must be

found and corrected. You should never have large errors. If you have large errors and can’t

find out why, then contact the TA or me for help. You shouldn’t have a report with incorrect

results.

While performing the experiment and making measurements, a detailed listing of the actions

should be kept in a laboratory notebook. The notebook should contain the schematics,

summary of the procedure, components’ and voltage sources’ measured values, expected results

calculations, and measurement results. The information in this notebook will document what

was done and can be used in court to support claims of inventorship. It will also assist when

writing the formal lab report and can be used in the exams for this course.

Therefore, to determine the results we expect, we must calculate by hand, these expected

results. So the readers of our report know and can check our work, we need to include these

calculations in the report. The more detail we can provide, the easier it will be to find the cause

of the error(s). Therefore, every lab report should have the assumptions stated and the detailed

calculations included in the Theoretical Analysis section of the report.

When the measurements are made, the results should be compared with the expectation to

determine if the desired results were obtained. This comparison should be included as a table

or tables in the lab report’s Verification Results section. The table should have a table number

and a meaningful, descriptive title. As described in the Laboratory Report Format, the table

should have a row for each measurement and the columns, in order, will be

The name of the measurement (such as VR1, the voltage across resistor R1), the expected value

with units (such as 10 V), the obtained results with units (such as 9.853 V), the difference

between expected and obtained results (such as 0.147 V), the percentage difference between

expected and obtained results (such as 1.47% from the calculation 0.147/10 x 100%), and last a

comment if the % error is significant enough to merit a comment. So the table for this single

measurement would be:

Name Expected Measured Error % Error Comment

VR1 10V 9.853V 0.147V 1.47% Error within tolerance

The results should not be adjusted or changed in any way. They should be report exactly as

they were produced. If the meter output was inf, then enter inf and do not change it to infinite.

The Discussion section of the report is where you can interrupt your results. This is where you

can describe how you view your results. This is where you explain the significance of what

you did and how it fits into past work and possible future work. You can discuss difficulties

and provide guidance on parts that need particular care.

Last, any documents, graphs, pictures or other evidence you want to include should be placed in

an Attachments section.

Now you should be ready to being:

a) and b) are the electronic circuits to simulate:

Figure 10: Circuits to Simulate for Lab Exercise

This second electrical circuit (b) has an AC, Alternating Current, Voltage source. This means

the electrical current first flows one direction then reverses and flows the opposite direction,

thus the current alternates.

In the resistors, the current and the voltage are in phase. That is, if the current is increasing

the voltage is increasing and if the current is decreasing the voltage is decreasing.

But the voltage current relationship is different on a capacitor, C1. The current and the

voltage are 90 degrees out of phase. This means that when the current is at its positive peak

value the voltages on the resistors are at their peak positive values. However, the capacitor

voltage is not at its peak value until ¼ of the period later, after the current has passed

through its peak. This phase shift is why the impedance of the capacitor cannot be just added

to the resistance of the resistors but it has to be vector summed with the resistances of the

resistors: .

See below for help with the analysis of the two circuits:

Figure 10: Mesh Analysis of Current Source Resistive Network

In circuit a) there are two loops. Loop 1, with loop current IL1, is formed by the loop

components Resistor R3 and the current source I1. Loop 2, with loop current IL2, is formed by

the loop components the Resistors, R1, R2, and R3. The loop current can be found by

determining the current of a loop component that is only part of the loop of interest. That is, it

is not part of more than one loop. These components are R1, R2, and I1. R3 is shared by both

loops. Since the current source I1 is only in Loop 1 then its current, 4A, is Loop 1’s current,

IL1.

Note: The direction for positive current is arbitrarily selected but convention has it usually

flowing clockwise in the loop. If the calculation determines the current is negative, this means

the current is flowing in the opposite direction.

Now to find Loop 2’s current we must use KVL on Loop 2. The Voltages around the loop must

sum to zero. Therefore (Equation 1)

VR1 + VR2 + VR3 = 0.

From Ohm’s Law, V = I x R:

R1 and R2 has Loop 2 current flowing through them:

VR1 = I x R1 and VR2 = I x R2 where I = IL2,

but R3 has two loop currents, IL1 and IL2 flowing in it and they are in opposite directions. The

net or resulting current magnitude is the difference between the two loop currents IL2 – IL1.

VR3 = (IL2 – IL1) x R3.

Putting this into equation 1 yields:

IL2 x R1 + IL2 x R2 + (IL2– IL1) x R3 = 0. => IL2 (R1 + R2 + R3) = 4 x R3

We know that Loop 1’s current, I L1 is 4A and R1 = 4 Ohm, R2 = 1 Ohm, and R3 = 5 Ohms

Substituting into the equations:

IL2 ( 4 + 1 + 5) = 4 x 5

Now we can solve for IL2. With IL1 and IL2 we can solve for the voltages on each component.

The to check our results we can sum the voltages around the loops and see that they sum to

zero.

For circuit b)

Figure 11 AC Voltage Source and Resistive – Capacitive Circuit.

Circuit b) has an AC voltage source. It is assumed that the voltage source can provide as much

current as needed by the circuit so the voltage is what is stated by the source. We must

determine this current to calculate the components’ voltages. Since the circuit is a series

circuit, all the components are serially connected together, the current for each component is the

same and is the loop current for this circuit. To determine the current, the impedance of the

entire circuit must be calculated and then divided into the voltage from the source. From Ohms

Law: I = V/Z, where Z is the “AC resistance (R)” of the circuit.

The impedance of the resistors, R1 & R2, are just their resistance, 10 kOhms and 100 Ohms

and there is no phase shift.

The impedance of the capacitor has a magnitude dependent on the frequency of the source and a

delay between the current and voltage reaching their peak values with the current being ahead

of the voltage. This is a 90 degree phase shift (1/4 of its period) between the capacitor voltage

and current. The magnitude of the phase shift (called the reactance Xc) is Xc = 1/(2 fC)

where in this case, f = 1000 Hz and C = 0.1 x 10-6

Farrads.

We must combine the two impedances to determine Z, but the resistors with zero phase shift

reach peak voltage when the current is at peak and the capacitor reaches peak voltage after the

current has reached peak. This means we can’t just numerically sum the resistors with the

capacitor impedance. There must be an adjustment made for the capacitor’s 90 degree phase

shift. This is adjusted by doing a vector sum where the capacitor impedance is at a right angle

to the resistor’s impedance.

Figure 12 Resistor – Capacitor Circuit Phasor Diagram

Since the Current and both the Resistors’ voltages are in phase they both lie on the X-axis in the

complex plane and the two resistor values can be numerically summed. The Voltage on the

capacitor lags the current by 90 degrees, so the capacitor lies on the negative Y-axis. The

resultant impedance of combining the resistors’ impedances with that of the capacitor

impedance is the vector Z. Its magnitude, |Z|, is given by the equations .

The current can be found by dividing the source voltage by this impedance.

Knowing the current we can find the voltage on each of the components.

Notice that these voltages around the loop do not sum to zero. This is because the

measurements are based on the peak voltages and the peak voltage for the capacitor occurs at a

different time from the resistors’ peak voltages. If the voltages of all the components are

measured at exactly the same instant in time, then these voltages will sum to zero and KVL

does still hold true.

Good luck and if you have trouble contact the TA or the instructor.