National Instruments Xmath Interactive Control Design Module ICDM - Manual (Page 44)

Chapter 4 PID Synthesis
Xmath Interactive Control Design Module 4-4 ni.com
Notice that there are at least two other commonly used forms for a PID
control law that differ from the one used in ICDM:
and
ICDM enforces a proper controller transfer function, that is, a finite high
frequency gain. Therefore, if the D term is on, ICDM will require at least
one HF rolloff term also to be on.
Opening the PID Synthesis Window
When you select the PID window from the Synthesis menu in the ICDM
Main window, the PID window first decides whether the current controller
transfer function has the form of a PID controller. If it does, then the PID
window sets its parameters (including the push buttons) to the values that
would yield the current controller, and then opens. In this case the current
controller remains unchanged. If the current controller does not have the
form of a PID controller, then a dialog box appears and warns the user and
offers several alternatives.
Manipulating the Controller Parameters
Each parameter can be changed using the slider, variable-edit box, or
graphically. To change the sign of the parameter or to change the parameter
to a value outside the current slider or plot range, you must use the
variable-edit box. Notice that negative values are allowed, but often
are not what you want.
The parameters also can be changed graphically by grabbing and dragging
the controller Bode plot in the following ways:
• To change the gain, with the gain parameter turned on, grab the
magnitude Bode plot anywhere except near the handles (dark circles)
on the plot. You now can drag the Bode plot up and down, which
changes the gain.
• To change the other parameters, listed in column four of Table 4-1,
grab the appropriate handle (dark circle) on either plot and drag it left
and right to the desired frequency, which is the inverse of the time
parameter. The associated slider and variable-edit box also will be
updated as you drag the handle.
C s ( ) K
p
= 1 1 + T
int
s T
diff
s +
⁄ ( )
+
C s ( ) K
p
= 1 T
int
s T
diff
s +
⁄
+