Entering Expressions in Analyses in NI Multisim

In NI Multisim 10.0 you have the ability to add expressions into analyses. The analysis tools in Multisim provide a sophisticated manner in which to study the characteristics of a circuit. In the Analysis Dialog Box (Figure 1), the output tab displays variables describing node voltages and branch currents in the circuit. These can all be outputted to the Grapher during the simulation and analysis process.

There are times, however, when you might want to take these variables and combine them into expressions, such as power, to evaluate important characteristics of the circuit. In Multisim this is done easily through the analysis options. In the following example you will perform the simple steps needed to create an expression while performing transient analysis on a RF Amplifier circuit.

Figure 1. The Analysis Dialog Box

Begin by opening up a sample circuit provided with your installation of Multisim.

1.Open up the example file <installation path>\samples\RFAmplifiers.ms9 and view the following circuit (Figure 2).

Figure 2: RF Amplifier Example

 

2. Go to the File menu - select Simulate»Analyses»Transient Analysis and then select the Output tab in the transient analysis dialog box.

You can now add an expression to analysis. The items in the Variables in Circuit scroll box (Figure 3) display the voltage and current values which can be grouped into expressions. For the purpose of this example, we will multiply the input by the output voltages. The output voltage is represented by the variable V(Output) and the voltage taken at the input is represented by the variable V(Input).

3. Press the Add Expression button.

4. In the Variables scroll box, select V(Output) and press Copy Variable to Expression. Now copy the ‘*’ symbol (to designate a multiplication) from the Functions scroll box, and click Copy Function to Expression. Now return to the Variables scroll box and select the V(Input) variable. Again, click Copy Variable to Expression. The analysis dialog box should now appear as it does in Figure 4.

5. Click the OK button.

6. You will notice the expression now appears in the Selected Variables for Analysis scroll box.

7. If you now simulate by clicking the Simulate button, you will see the transient analysis waveform of our expression (Figure 5).

Note: To finish the simulation quicker, simply lower the analysis end time on the Analysis Parameters tab of the Transient Analysis dialog box. The End time (TSTOP) parameter in this example is set to 1e-005.

Related Links:
Learn more about Electronics Workbench Multisim
Download the Multisim Evaluation Version

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