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.

Bemerkung

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).

Bemerkung

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