National Instruments Xmath Interactive Control Design Module ICDM - Manual (Page 30)

Chapter 2 Introduction to SISO Design
© National Instruments Corporation 2-15 Xmath Interactive Control Design Module
(if it was not already) but otherwise does not move. Thus, to make a pair of
complex poles real, you first drag one of them near the real axis and release.
Then you select one of these poles again, and this time drag it left or right.
This will cause the pair to become real.
Adding/Deleting Poles and Zeros
This section describes how you are allowed to add or delete poles or zeros
in some windows. Bear in mind that ICDM may not allow you to add or
delete a zero or pole in certain cases—for example, if the action would
result in a nonproper controller. In this situation, you will be warned with
a dialog box which opens.
To add a zero, click the Add Zero button that is near the plotting area, or
select the Add Zero entry from the Edit menu. In some cases there is an
accelerator for this, such as typing
z in the window. These actions will
cause the cursor to become a crosshairs symbol. If you click the left mouse
button with the cursor very near the real axis, then you will create one real
zero. If you click the left mouse button with the cursor farther from the real
axis, then you will create a pair of complex conjugate zeros. Creating a pole
is similar; typing
p in the window is the accelerator for creating a pole or
complex conjugate pole pair. To abort a pole or zero add operation, click
the left mouse button with the cursor outside the plot area.
To delete a pole or zero, press the <Ctrl> key near the plotting area, select
the Delete entry from the Edit menu, or enter
d in the window. These
actions will cause the cursor to become a skull and crossbones symbol.
Then click the left mouse button with the cursor near the pole or zero that
you want to delete. If the pole or zero is complex, then its complex
conjugate also will be destroyed.
You always can select Undo in the Edit menu to restore deleted poles or
zeros back, provided you have not made any other changes since deleting.
To abort a delete operation, click the left mouse button with the skull and
crossbones cursor in a free area of the plot.
Adding/Deleting Pole-Zero Pairs
When you add (or delete) a pole or zero, you can drastically change the
transfer function that you are editing. In some cases, it may be better to add
(or delete) a pole-zero pair—that is, a pole and zero in exactly the same
location. Adding a pole-zero pair does not change the transfer function at
all until the pole and zero are moved apart.