Teach Tough Concepts: Superposition with NI Multisim and LabVIEW

Publish Date: Oct 26, 2012 | 16 Ratings | 4.25 out of 5 | Print | 1 Customer Review | Submit your review

Overview

Learn how you can use National Instruments educational software and hardware to teach the fundamental circuits principle of superposition. Along with accompanying textbooks, NI LabVIEW and NI Multisim interface directly with NI ELVIS and NI myDAQ to provide a complete solution for circuits theory, simulation, and physical implementation and validation. The following document will explain how to achieve this result in your classroom.

By the end of this tutorial, you will be able to:
• Build and simulate a circuit that can be solved using superposition in NI Multisim
• Build the circuit on a breadboard and validate the voltage using NI myDAQ or NI ELVIS II and LabVIEW
• See a solution for reinforcing the principle of superposition by allowing students to quickly try different permutations of circuits

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Download example programs and follow the tutorial below to recreate the lab demonstrated in the above video.

Background

Traditionally, fundamental concepts such as superposition are taught with pencil and paper or on the chalkboard.  These fundamental concepts have not changed in nature, but the way that they can be taught has evolved.  Let's have a look at a circuit that can be solved using superposition:

Figure 1. A Basic Linear Circuit with 2 Independent Voltage Sources

The basic circuit solving method using superposition is as follows:

1. Identify the source to be isolated
2. Set all remaining independent sources to zero by shorting voltage sources and setting current sources to an open circuit
3. Solve for the voltage across each element of the circuit
4. Repeat for each remaining voltage or current source
5. Summate the individual voltage drops to find the overall voltage drop across the element due to all independent source used in conjunction with one another

Again, used superposition is traditionally taught and solved using a pencil and paper.  So is there an easier way to teach and learn this concept?  Can the concept be better reinforced by allowing students to quickly try different permutations of circuits and then build the physical circuit and validate it?

Let's start by integrating NI Multisim to build and simulate the circuit using the procedure below.  We will then follow by building the circuit on a breadboard and validate the voltage using NI myDAQ or NI ELVIS II and LabVIEW to acquire the analog voltage.

Simulation: Multisim Step-by-Step Procedure

Note: If you do not have NI Multisim installed on your local machine, you can Download and Evaluate Multisim Education Edition free for 30 days.

If you would like to interface with NI myDAQ or NI ELVIS-II directly in Multisim for simulation, you will first need to download and install the latest version of the NI ELVISmx device driver.  Then open Multisim and select File»New»NI myDAQ Design or NI ELVIS II Design.

Use the following procedure to create the above circuit in Multisim.  Single-pole, double-throw (SPDT) switches are used to short out the DC voltage sources, and a relay can be used to open the circuit to any current sources.  A simulated voltmeter is used to measure the voltage drop.  The solution Multisim file is included at the end of this document.

1. Open NI Multisim by navigating to Start»All Programs»National Instruments»Circuit Design Suite»Multisim
1. A new circuit is created by default
2. Create the 5 VDC power sources
1. Right-click the blank schematic and select Place Component...
2. Select Sources for the Group
3. Select Power_Sources for the Family
4. Select DC_Power for the Component and select OK
5. Left-click to place the first voltage source on the schematic
6. Select Close when the Select a Component dialog box returns
7. Right-click the voltage source and select Copy
8. Right-click the schematic and select Paste and left-click to place the second voltage source
9. Double-click either supply and change the Voltage (V): to 5 V
10. Repeat for the remaining voltage supply
11. The circuit should look similar to Figure 2

Figure 2. Two Independent 5V DC Voltage Sources

1. Place the SPDT switches to short the circuit voltage supplies
1. Right-click the blank schematic and select Place Component...
2. Select Basic for the Group
3. Select SWITCH for the Family
4. Select SPDT for the Component and select OK
5. Hold Ctrl and press R three times to rotate the component 270°
6. Left-click to place the first SPDT switch below one voltage source and connect the voltage source to one of the SPDT's poles
7. Wire the two components together as seen in Figure 3
8. Repeat for second SPDT switch and voltage source

Figure 3. Addition of SPDT Switches

1. Place horizontally oriented resistors
1. Right-click the blank schematic and select Place Component...
2. Select Basic for the Group
3. Select RESISTOR for the Family
4. Type 3.8k in the Component input box and select OK
5. Left-click to place the resistor above and to the right of the left-most voltage source
6. Wire the output of the left most voltage source to the left input of the 3.8kΩ resistor
7. Wire the second pole of the SPDT switch to the same left input of the 3.8kΩ resistor to form a node
8. Repeat process for other voltage source and SPDT switch with a 1.2kΩ resistor
9. The schematic should now appear similar to Figure 4

Figure 4. Addition of Horizontal Resistors

1. Place the vertically oriented resistors
1. Right-click the blank schematic and select Place Component...
2. Select Basic for the Group
3. Select RESISTOR for the Family
4. Type 1.0k in the Component input box and select OK
5. Hold Ctrl and press R once to rotate the resistor 90°
6. Left-click to place the resistor to the right of the left-most voltage source
7. Wire the output of the 3.8kΩ resistor to the top input of the 1.0kΩ resistor
8. Wire the output of the 1.0kΩ resistor to the input of the left-most SPDT switch
9. Repeat process for other vertical 3.0kΩ resistor
10. The schematic should now appear similar to Figure 5

Figure 5. Addition of Vertical Resistors

1. Add the voltmeter to measure to potential difference
1. Right-click the blank schematic and select Place Component...
2. Select Indicators for the Group
3. Select Voltmeter for the Family
4. Select Voltmeter_H for the Component and select OK
5. Left-click to place the horizontal on the schematic
6. The schematic should now appear similar to Figure 6

Figure 6. Circuit after adding the voltmeter

1. Add a ground terminal to ground the circuit
1. Right-click the blank schematic and select Place Component...
2. Select Sources for the Group
3. Select POWER_SOURCES for the Family
4. Select GROUND in the Component input box and select OK
5. Left-click to place in the lower-middle of the circuit
6. Wire to one side of the circuit
7. Select Place»Junction and left-click on the input terminal of the Ground pin
8. Wire the ground pin to the other side of the circuit
9. The schematic should now appear similar to Figure 7

Figure 7. Complete circuit after adding the ground terminal

1. Press the Run button to simulate the circuit
1. Left-click the SPDT switches to turn them on or to short them
2. The total voltage drop should be equal to the sum of individual contribution as seen on the voltmeter digital display

Figure 8. Principle of Superposition with Multisim Voltmeter

Validation: Step-by-step Procedure in LabVIEW

Use the following procedure to use LabVIEW to interface with NI myDAQ or NI ELVIS-II hardware to physically validate the principle of superposition.  You can use a breadboard, resistors, and wire to build the circuit and connect to the input terminals of the DAQ device.  The LabVIEW VI is attached at the bottom of the document.

1. Ensure that you have connected your NI hardware device (NI ELVIS-II or NI myDAQ) to your local machine
2. Open NI Measurement and Automation Explorer and verify that your DAQ device is labeled Dev1 (Device 1)
1. If not, right-click your device and select Rename
3. Connect your circuit to your DAQ device according to Figure 9

Figure 9. Connection Diagram for Superposition Circuit

1. Open the attached mydaq_superposition.vi LabVIEW VI file
1. Navigate to the block diagram to familiarize yourself with the programming
2. Low-level DAQmx API is used in this example, but the same can be accomplished using DAQ Assistant Express VIs
1. Run the VI and change the Voltage Supply controls while running to observe the results
1. Zero each voltage source to find individual contributions from the sources
2. Verify the total voltage drop is equal to the individual voltage drops

Figure 10. Changing V1 Input on Front Panel of Superposition VI

The NI Electronics Education Platform

The NI Electronics Education Platform is an end-to-end tool chain designed to meet the needs of students and educators. It is an ideal mix of integrated hardware and software that guides students through the engineering and design process from understanding circuit theory to developing and simulating designs, and then on to prototyping and validation.

The platform consists of NI Multisim, the NI ELVIS prototyping workstation, and NI LabVIEW and SignalExpress. NI Multisim provides intuitive schematic capture and SPICE simulation to help students explore circuit theory and investigate behavior. Multisim also includes a 3D prototyping environment which can help students to bridge from a software environment to real-world designs. The NI ELVIS and NI myDAQ are prototyping platforms that allows students to quickly and easily develop their circuits and take measurements interactively using multiple built-in virtual instruments such as an oscilloscope, multimeter, variable power supply, and function generator. NI LabVIEW and SignalExpress are ideal environments which offer intuitive interfaces to measurements, and allow students to compare their measurements and simulations on the same display.

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Customer Reviews
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contact control from LabVIEW  - Jun 14, 2012

s it possible to add two-state contacts to Multisim and control them from LabVIEW in a boolean way? Thanks.