PID

 Function Block A function block groups an algorithm and a set of private data. It has inputs and outputs. - PID "Proportional-Integral-Derivative" A PID controller is a generic control-loop feedback mechanism widely used in industrial control systems. An "error" occurs when an event or a disturbance triggers off a change in the process variable. A PID controller attempts to correct the error between a measured process variable and a desired setpoint by calculating and then outputting a corrective action that can adjust the process accordingly loop

See Regulation for more information.

Inputs

Input	Data Type	Range	Unit	Default	Description
AUTO	BOOL				TRUE = normal mode FALSE = manual mode
DEADB_ERR	REAL				Hysteresis on PV. PV is considered as unchanged if it is both: Greater than (PVprev - DEADBAND_W). Less than (PRprev + DEADBAND_W).
FFD	REAL				Disturbance value on output.
I_ITL_ON	BOOL				If TRUE, the integrated value is reset to I_ITLVAL.
I_ITLVAL	REAL				Reset value for integration when I_ITL_ON is TRUE.
I_SEL	BOOL				If FALSE, the integrated value is ignored.
INT_HOLD	BOOL				If TRUE, the integrated value is frozen.
KP	REAL				Gain.
PV	REAL				Process value.
SP	REAL				Set point.
TD	REAL				Derivation factor.
TI	REAL				Integration factor.
TS	TIME				Sampling period.
XMAX	REAL				Maximum output value.
XMIN	REAL				Minimum allowed output value.
Xout_Manu	REAL				Output value in manual mode.

Outputs

Output	Data Type	Range	Unit	Description
ER	REAL			Last calculated error.
Xout	REAL			Output command value.
Xout_D	REAL			Last calculated derivated value.
Xout_HLM	BOOL			TRUE if the output value is saturated to XMAX.
Xout_I	REAL			Last calculated integrated value.
Xout_LLM	BOOL			TRUE if the output value is saturated to XMIN.
Xout_P	REAL			Last calculated proportional value.

Remarks

• It is important for the stability of the control that the TS sampling period is much bigger than the cycle time.
• Output of the PID block always starts with zero.
  • The value varies per the inputs provided upon further cycle executions.
• In the FFLD Language, the output rung has the same value as the AUTO input, corresponding to the input rung.

Diagram

FBD Language

FFLD Language

(* ENO has the same state as the input rung. *)

IL Language

(* MyPID is a declared instance of PID function block. *)
Op1: 	CAL MyPID (AUTO, PV, SP, XOUT_MANU, KP, TI, TD, TS, XMIN, XMAX, I_SEL, I_ITL_ON, I_ITLVAL, DEADB_ERR, FFD)
	FFLD  MyPID.XOUT
	ST "Structured text"
A high-level language that is block structured and syntactically resembles Pascal  XOUT
	FFLD  MyPID.ER
	ST  ER
	FFLD  MyPID.XOUT_P
	ST  XOUT_P
	FFLD  MyPID.XOUT_I
	ST  XOUT_I
	FFLD  MyPID.XOUT_D
	ST  XOUT_D
	FFLD  MyPID.XOUT_HLM
	ST  XOUT_HLM
	FFLD  MyPID.XOUT_LLM
	ST  XOUT_LLM

ST Language

(* MyPID is a declared instance of PID function block. *)
MyPID (AUTO, PV, SP, XOUT_MANU, KP, TI, TD, TS, XMIN, XMAX, I_SEL, I_ITL_ON, I_ITLVAL, DEADB_ERR, FFD);
XOUT := MyPID.XOUT;
ER := MyPID.ER;
XOUT_P := MyPID.XOUT_P;
XOUT_I := MyPID.XOUT_I;
XOUT_D := MyPID.XOUT_D;
XOUT_HLM := MyPID.XOUT_HLM;
XOUT_LLM := MyPID.XOUT_LLM;