Ft pi

Type Function module

Input IN	REAL (input signal)
KP	REAL (proportional part of the controller)
KI	REAL (integral part of the controller)
ILIM_L	REAL (lower limit of the integrator output)
ILIM_H	REAL (upper limit of the integrator output)
IEN	BOOL ( Enable for Integrator )
RST	BOOL (asynchronous reset input)
Output Y	REAL (output of the controller)
LIM	BOOL (TRUE if the output has reached a limit)
FT_PI is a PI controller which works following the formula
	Y = KP * IN + KI * INTEG(IN)
The input values ILIM_H and ILIM_L limits the working area of the internal integrator. With RST, the internal Integrator can always be set to 0. The output LIM indicates that the Integrator has reached one of the limits ILIM_L oe ILIM_H. The PI controller is free running and uses the trapezoidal rule to calculate the integrator for the highest accuracy and optimal speed. The default values of the input parameters are predefined as follows	KP = 1, CI = 1, ILIM_L= -1E38 and ILIM_H = +1E38.
Anti Wind-Up	Control modules with Integrator tend to the so-called Wind-Up Effect. A Wind-Up means that the integrator module continuously run again because, for example, the control signal Y is at a limit and the system can not compensate the deviation, which then leads to subsequent transition into the control range until a long and time-consuming dismantling of the integrator value and the scheme only respond delayed. Since the integrator is only necessary to compensate the deviation for all other control units, and the range of the integrator should be limited with the values of ILIM. The Integrator then reaches a limit and stops remaining at the last valid value. For other wind- Up Action, the Integrator can be controlled with the input IEN = FALSE any time separately, the Integrator only runs when IEN = TRUE.
The following graph illustrates the internal structure of the controller
	FT_PI can be used in conjunction with the modules CTRL_IN and CTRL_OUT to build a PI controller.