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Biomedical Application: Multisim Simulation

with an ECG Amplifier

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Overview

This example program which include NI Multisim and NI LabVIEW is one in a series which

showcases the power of using advanced LabVIEW instruments within the simulation

environment.

Note: This document is included in a free courseware packet. Download the

Bioinstrumentation Courseware Packet now.

All instruments are based upon a virtual instrument template found in the Multisim sample

folder. Any LabVIEW user can easily take this template and define an instrument which can

input complex signals, or visualize simulation data within Multisim.

This level of advanced design flexibility is only available to the professional design engineer

with the National Instruments platform of Multisim and LabVIEW.

Downloads

Filename: 5925_ecg_amplifier.zip

Requirements: View

Please Note

SPICE simulation, the language by which Multisim emulates circuit design behavior, does not

run in real-time. This means that if a real-world signal is acquired by a LabVIEW instrument it

cannot be directly injected into simulation, since the measurements will be running at different

rates (real time vs. simulated time).

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Purpose Of This Instrument

In the growing world of Biomedical engineering, the need to be able to quickly design circuitry

which interfaces to a human signal is a common design problem. An amplifier for example can

be designed in a circuit simulation package, however the signals which will interface to that

particular circuit will be simple simulation stimuli (such as a sine wave, square wave etc...). To

truly test a biomedical amplifier, you need to be able to interface the design to a real signal.

Using this unique LabVIEW instrument you are able to define a human electrocardiogram

(ECG) signal, and have amplify it through a circuit created in Multisim.

This LabVIEW instrument, built custom for NI Multisim produces a raw electrode

ECG waveform. Since this instrument is built in LabVIEW we have a number of analysis, and

signal altering functions available to us. In this case we are able to add common mode voltage, as

well as noise components to alter the signal to improve the test and validation of our circuit.

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Installation Instruction

Download the archived file to the desktop. You simply need to:

1. Close NI Multisim if open. 2. Open the attached 5925_ECG Amplifier.zip file. 3. Select My Computer. 4. Browse to C:\Program Files\National Instruments\Circuit Design Suite 10.1\lvinstruments. 5. Save the ECG Electrode.llb file from the zip file to this folder.

Instrument Features

The ECG Electrode program consists of 2 main controls, the Common Mode Voltage and

Frequency Content. Both of these inputs can be changed to change the values, and alter

(common mode voltage) or apply noise components (frequency content) to the signal which is

being sent to a circuit.

Using the Instrument and Example Circuit

This instrument will use the example circuit that is in the attached 5925_ECG Amplifier.zip file

folder.

1. Open Multisim by selecting Start > All Programs > National Instruments > Circuit Design Suite 10.1 > Multisim 10.1.

2. Go to File > Open. 3. Browse to the ECG Amp with ECG Signals.ms10 file from the 5925_ECG Amplifier.zip file. 4. You will see a complete amplifier based upon two common Op-Amps. 5. In Multisim select the LabVIEW icon in the instrument toolbar (as seen below). 6. Select ECG Signals. This is the name of the ECG Electrode instrument (as seen below).

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7. Place the instrument onto the schematic as seen below, and connect it to the V_BODY_N and V_BODY_P wires.

8. The circuit is now complete.

9. Double-click on the XLV1 instrument (the ECG electrode stimulus) 10. Set the Common Mode Voltage to 4.7 11. Set the Frequency Content to 8.

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12. You are now ready to begin simulating the circuit. 13. Click on the run button on the simulation toolbar.

14. Double-click on the oscilloscope instrument (XSC1) in the bottom right-hand corner of the screen.

15. You will see the red ECG signal waveform from the Raw ECG Electrodes be amplified by the amplification circuit.

16. Stop the simulation (by selecting the stop button in the simulation toolbar). 17. Change the Common Mode Voltage to any value. 18. Run the simulation and view the change in the ECG signal in the oscilloscope.

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Requirements

Filename: 5925_ecg_amplifier.zip

Software Requirements

Language(s): LabVIEW