The Transient Analysis mode available in ELECTRO, OERSTED, and KELVIN has the capability to create virtually any desired time dependent source with a library of Standard signals, an algebraic Function editor, and the ability to read in Tables from text files.
Often the desired source can be constructed by using one or more of the Standard predefined time signals.
Examples of the Standard time signals available are shown below. These signals are typical of the type found in mathematical handbooks.
Once you’ve selected a signal from the drop down list, you can set the relevant parameters for the signal in the numeric field boxes. At right we show an example of a Periodic Triangular Pulse Source that is defined by four parameters; a Start time, an Amplitude, a Pulse width and a Period (if desired a fifth parameter, Stop time, could also be specified).
Graphs of the time variation of the source can be plotted using the [Plot Source] button. The [Plot All] button produces graphs of all component signals in addition to the resultant source.
For the parameter settings given above, the source will be the time function shown in the plot below.
You can enter signals as closed form functions of time by selecting the Function radio button and entering the signal as an algebraic expression. An example of this is shown at right.
A plot of the resulting signal is shown below.
Note that the arguments of trigonometric functions are assumed to be in degrees. Also note that there should be no extra spaces in formulas as these will cause parsing errors.
Table Defined Signals
As a final option, you can define signals by creating text files containing two-column data tables.
In the example shown at right, the first column represents discrete time instants, and the second column represents the corresponding signal values. Note that the data points describe a signal with zero initial value followed by a positive pulse of 0.4 starting at t=0.25 and lasting till t=0.5. After another zero interval, a negative pulse of -0.2 starts at t=0.8 and lasts until t=0.9. The signal then returns again to zero.
At right we show the Component Signal Properties section as it appears when the Table radio button is selected.
Click the file open button to locate to the desired data file.
Note also that the Linear radio button has been selected in the Interpolation section.
The resulting time signal is shown below. Note that Linear interpolation should be used for signals with sharp transitions, but Nurbs should be used for continuous signals.