Using a Comparison Display To Show The Difference Of Two SPICE Based Signals

Overview

This example program is part of a series of LabVIEW based virtual instruments that can be used from inside Multisim.  All instruments are based on the virtual instruments templates you can find in your Multisim’s sample folder. There are two main categories of instruments:

• Input Instrument; takes simulation data from your schematic and processes them in the virtual instrument (e.g. custom display, specific analysis, output to real world)
• Output Instrument; inputs signals to a Multisim schematic to drive a simulation (e.g. acquire data from real world I/O, custom and arbitrary waveforms)

 

Note for using real world I/Os

Due to the nature of SPICE, all real world data that will be used to drive a circuit need to be acquired before a simulation is started. Data output to a real world device can be done while simulation is running, however continuous updates can’t happen in real-time, as SPICE simulations don’t have a real-time timebase.

 

Purpose Of This Instrument

Multisim’s oscilloscopes help designers to gain a better understanding of the transient behavior of their circuit. The oscilloscope comes with multiple powerful functions such a triggering, AC and DC coupling and different display options. However, there is always a time a user is looking for a specific function, that a vendor defined instrument can’t offer.

This new Comparison Display is an example of how LabVIEW based instruments can be tailored to an exact purpose. This instrument offers the possibility two plot two channels and the difference between the two as well to normalize on any of the input channels. The user of this instrument automatically benefits from the functions build into the LabVIEW chart. Zooming in on a particular trace, switching between manual and auto and changing trace properties can all happen on the fly.

 

Installation Instruction

Unpack the archive to the Multisim installation directory. The table illustrates the files that will be copied to your harddrive.

Type	Name	Location	Application
Instrument	Comparison_Display.llb	..\lvinstruments	Multisim
Example	Test Comparison_Display.ms10	..\ samples\LabVIEW Instruments\ Comparison Display	Multisim
Project	Comparison Display.lvproj	..\ samples\LabVIEW Instruments\ Comparison_Display	LabVIEW
Source	Comparison Display.llb	..\ samples\LabVIEW Instruments\ Comparison_Display	LabVIEW

 

Instrument Features

The Comparison Display features tip strips for all controls. Hover with your mouse cursor over any of the controls and specific information will be displayed.

• Interface Controls
  • Sample Rate [Hz] accounts for the data exchange between NI Multisim and the LabVIEW based instrument (you need to restart the simulation if you change the value)
  • Interpolation Method sets the method that will be used to account for not evenly distributed SPICE data
• Comparison Controls
  • Normalize allows the user to select a channel (Ch A or Ch B) to be used as a reference (this channel will be set to 1)
  • Difference allows to toggle which channel is the minuend and which the subtrahend
• Display Controls
  • Use default chart options to set trace properties, scaling, axis names and zoom

 

 

How To Use This Instrument

1. Open Multisim and create your circuit
2. Add the Comparison Display to your circuit
   1. Access the Comparison Display from the instrument toolbar
   2. Place it on your schematic
   3. Wire the desired input pins 
3. Start the simulation
4. Double click the instrument symbol to open the interface
   1. Change parameters if necessary
   2. Right click on an axis to enable/disable auto scaling
   3. Left click on the plot legend to change trace properties
   4. Click on the zoom symbol (magnifying glass) to zoom in/out

[+] Enlarge Image

 

Additional Resources

Search ni.com for more LabVIEW based instruments for NI Multisim

Tutorial on "How To Create A LabVIEW Based Instrument For NI Multisim"

Tutorial on "Assure Compatibility of LabVIEW based Instruments across different NI Multisim versions"

 

Note: You only need NI LabVIEW to create or edit and an instrument. NI LabVIEW doesn’t need to be installed on the machine where you intend to run Multisim.

Requirements

Filename: comparison_display.zip

Software Requirements

Application Software: LabVIEW Base Development System 8.2, Multisim Base Edition 9.x
Language(s): LabVIEW

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