4.3 Creating labview instruments to instrument circuit simulations

Creating labview instruments in multisim

Multisim ships with four different virtual NI LabVIEW instruments: a microphone, speaker, signal generator, andsignal analyzer. The symbols are shown in Figure 1 and the speaker front panel is shown in Figure 2.

Microphone - Records audio from the computer sound device and outputs the sound data as a signal source.

Speaker - Plays input signal using the computer sound device.

Signal Generator - Generates and outputs a sine, triangle, square, or sawtooth wave.

Signal Analyzer - Displays time-domain data, auto power spectrum, or running average of input signal.

Custom instruments can be created using the NI LabVIEW graphical development environment. Instruments that arecreated using NI LabVIEW can take advantage of the full functionality of the NI LabVIEW development system including dataacquisition, instrument control, mathematical analysis, and so on.

For example, you can create an instrument that acquires data from the real world using a National Instruments dataacquisition device or modular instrument. Multisim will then use that data as a signal source for circuit simulation.

You can also create an instrument that displays simulation data simultaneously with multiple measurements(running average and power spectrum, for example) made from that simulation data.

NI LabVIEW instruments can be either input instruments or output instruments. Input instruments receivesimulation data for display or processing. Output instruments generate data to use as a signal source in simulation. A NI LabVIEWinstrument cannot be both an input and output instrument.

Additionally, input and output instruments behave differently. Input instruments continuously receivesimulation data from Multisim while simulation is active.

In contrast, at the beginning of circuit simulation, output instruments will first generate a finite amountof data and return that data to Multisim. Multisim will then use that data for circuit simulation. Output instruments do notcontinuously generate data while simulation is running. To cause an output instrument to generate new data, you must stop and restartsimulation.

Output instruments allow the user or creator of the instrument to determine whether the instrument repeats theoutput data. The LabVIEW instrument must be configured to repeat its output data periodically, or else the simulator will assume theoutput is 0V once it has no data remaining from the instrument. Alternatively, if you configure the instrument and repeat theoutput data, the instrument will loop and repeat its output periodically until the simulation has stopped.

Input instruments allow the user or creator of the instrument to set a sampling rate. This sampling rate is therate at which the instrument receives data from Multisim. This sampling rate is analogous to the sampling rate you would set for aphysical data acquisition device or modular instrument that acquires data from the real world. You should observe the Nyquistsampling theorem when choosing a sampling rate for your instrument. Note that the higher the value of the sampling rate, the slowersimulation will run.

To create and modify NI LabVIEW instruments, you must have the NI LabVIEW 8.0 (or later) DevelopmentSystem.

To use NI LabVIEW instruments, you must have the NI LabVIEW Run-Time Engine installed on your computer. Theversion of this Run-Time Engine must correspond to the version of the NI LabVIEW Development System used to create the instrument. The Multisim installer includes the NI LabVIEW Run-Time Engine 8.0 as part of the Electronics Workbench SharedComponents installation.