Adding Instruments to Your Circuit

This chapter gives you a brief overview of Multisim’s instrument functions and takes you through the steps of adding an instrument to your circuit. Multisim offers a variety of virtual instruments. This chapter describes the oscilloscope.

Introduction

Multisim provides a number of virtual instruments. You use these instruments to measure the behavior of your circuits. These instruments are set, used and read just like their real-world equivalents. They look and feel just like the instruments you’ve seen and used in a lab. Virtual instruments are one of the best and easiest ways of examining your circuit’s behavior by displaying the results of simulation.

The instrument toolbar is displayed by default. If your instrument toolbar is not displayed, click the Instruments button on the Design Bar. When you click this button, the Instruments toolbar appears. It includes one button for each instrument.

Virtual instruments have two views: the instrument icon you attach to your circuit, and the opened instrument, where you set the instrument’s controls and display options.

Adding and Connecting Instruments

For the purposes of this tutorial, we want to add an oscilloscope to the circuit. Either carry on with the circuit you have been creating so far, or open the file tut2.msm (which has been properly wired) from the Tutorial folder and proceed.

Step 1: Add an oscilloscope

! To add the oscilloscope:

1. Click the Instruments button in the Design Bar. The Instruments toolbar appears.

2. Click the Oscilloscope button and move your cursor to the circuit window. Your cursor will appear as the ghost image of the instrument.

3. Move the cursor to the right side of your circuit and click.

4. The oscilloscope icon appears on the circuit window.

5. You now need to wire the oscilloscope into your circuit.

Step 2: Wire the oscilloscope to the circuit

! To wire the oscilloscope into your circuit:

1. Click the A terminal on the oscilloscope icon and drag a wire to the junction between the output of U1 and R2.

2. Click the B terminal on the oscilloscope icon and drag a wire to between Q2 and C1.

Your circuit should look like this:

Configuring Instrument Settings

Each virtual instrument provided by Multisim includes its own series of optional settings that control its display.

! To open the oscilloscope, double-click the oscilloscope icon. The oscilloscope looks like this:

The time base section of the scope’s panel controls the scale of the oscilloscope’s horizontal or x-axis when comparing magnitude against time (Y/T)

To get a more readable display, adjust the timebase in inverse proportion to the frequency— the higher the frequency, the lower (or more magnified) the time base.

! To set the time base for our circuit:

• Set the timebase scale (which should use the waveform magnitude against time (Y/T axes) to 20 us/Div to best display the frequencies in our circuit.

• Set the Channel A scale to 5V/Div, and click DC.

• Set the Channel B scale to 500 mV/Div, and click DC.