PID_FIXCYCLE (FB)

FUNCTION_BLOCK PID_FIXCYCLE

Represents a PID controller for which the cycle time can be set manually

A PID controller continuously calculates an error value e(t) as the difference between a desired set point and a measured process variable. The PID contoller applies a correction based on proportional, integral, and derivative terms (sometimes denoted P, I, and D respectively) which give their name to the controller type.

Note

For fast and fix tasks it is recommended to use PID_FIXCYCLE instead of PID, because the cycle time is defined accurately, whereas PID only can measure the cycle time with a maximum accuracy of milliseconds. In case of very short cycles (1ms) this might lead to a rough run (see PID).

Note

It is not necessary to readjust the controller parameters (KP, TN, TV) if the cycle time changes.

For more information see: PID.

InOut:

Scope	Name	Type	Initial	Comment
Input	ACTUAL	REAL		Actual value, process variable
	SET_POINT	REAL		Desired value, set point
	KP	REAL		Proportionality const. P
	TN	REAL		Reset time I in sec
	TV	REAL		Rate time, derivative time D in sec
	Y_MANUAL	REAL		Y is set to this value as long as MANUAL = TRUE
	Y_OFFSET	REAL		Offset for manipulated variable
	Y_MIN	REAL		Minimum value for manipulated variable
	Y_MAX	REAL		Maximum value for manipulated variable
	MANUAL	BOOL		TRUE: Manual: Y is not influenced by controller FALSE: Controller determines Y
	RESET	BOOL		TRUE: Sets Y output to Y_OFFSET and reset integral part
	CYCLE	REAL		Time in s between two calls
Output	Y	REAL		Manipulated variable, set value
	LIMITS_ACTIVE	BOOL	FALSE	TRUE: Set value would exceed limits Y_MIN, Y_MAX
	OVERFLOW	BOOL	FALSE	Overflow in integral part