Description
Original instructions
Function description
This Function block enables the autotuning of the PID controller (PIDFF: Complete PID controller, PI_B: Simple PI controller).
Autotuning stabilizes the control when starting the system and, in so doing, saves time.
EN and ENO can be configured as additional parameters.
Algorithm
The algorithm is based upon heuristic controls, as with the Ziegler Nichols method. Initially, an analysis corresponding to approximately 2.5 times the reaction time of the open loop is performed. Through this, the process can be identified as a process of the first order with delay.
Building on this model, a control parameter set based on heuristic controls and historical data is created.
The parameter range is determined by the ’perf’ criteria. In this individual case, this factor gives the highest rank to the reaction time to disturbances or stability.
The algorithm is applied to the following process types :
Important characteristics
The block has the following characteristics
Operating mode
The various operating modes of the autotuning and their priorities in descending order of validity are shown in the following table:
Operating mode
TR_S
START
Tracking
1
0 or 1
Autotuning
0
1
On completion of the autotuning, the TRS output is set to 0, and the servo-loop is reset to its previous operating mode (manual or automatic). If the autotuning fails, the TRI variable will be set back to the value before autotuning was started and the servo-loop will be reset to its previous operating mode.
Representation in FBD
Representation:
* 
Parameters of the autotuned controller (Para_PIDFF, Para_PI_B,etc.)
Representation in LD
Representation:
* 
Parameters of the autotuned controller (Para_PIDFF, Para_PI_B,etc.)
Representation in IL
Representation:
CAL AUTOTUNE_Instance (PV:=ProcessValue, SP:=Setpoint, 
    RCPY:=RecopyRealCommand, START:=StartAutotuning, 
    PREV:=ReturnToPreviousValues, PARA:=Parameters, 
    TR_I:=InitializationInput, TR_S:=InitializationSequence, 
    PV_O=>PV_InputImage, SP_O=>SP_InputImage, 
    PARA_C=>ParametersToBeTuned, TRI=>TR_I_InputImage, 
    TRS=>TR_S_InputImage, INFO=>Information, 
    STATUS=>Statusword)
Representation in ST
Representation:
AUTOTUNE_Instance (PV:=ProcessValue, SP:=Setpoint, 
    RCPY:=RecopyRealCommand, START:=StartAutotuning, 
    PREV:=ReturnToPreviousValues, PARA:=Parameters, 
    TR_I:=InitializationInput, TR_S:=InitializationSequence, 
    PV_O=>PV_InputImage, SP_O=>SP_InputImage, 
    PARA_C=>ParametersToBeTuned, TRI=>TR_I_InputImage, 
    TRS=>TR_S_InputImage, INFO=>Information, 
    STATUS=>Statusword) ;
Parameter description AUTOTUNE
Input parameter description:
Parameter
Data type
Meaning
PV
Process value
SP
REAL
Setpoint
RCPY
REAL
Copy of the actual manipulated variable
START
"0 → 1" : Starting the autotune
PREV
BOOL
Reverting to the previous controller settings
PARA
Parameter
TR_I
REAL
Start input
TR_S
BOOL
Start command
Output parameter description:
Parameter
Data type
Meaning
PV_O
REAL
Copy of the actual value PV
SP_O
REAL
Copy of the SP input
PARA_C
Parameters of the autotunable controller (Para_PIDFF or Para_PI_B)
Control parameters
TRI
REAL
Copy of the TR_I input
TRS
BOOL
Copy of the TR_S input
INFO
Information
STATUS
Status word
Parameter description Para_AUTOTUNE
Data structure description
Element
Data type
Meaning
step_ampl
Value of the output actuating pulse (expressed in output scale values out_inf, out_sup)
tmax
Duration of the actuating pulse in automatic tuning
perf
REAL
Performance index between 0 and 1
plant_type
Reserved word
Info_AUTOTUNE parameter description
Data structure description
Element
Data type
Meaning
diag
Double word used for diagnosis
p1_prev
Previous value of parameter 1
p2_prev
REAL
Previous value of parameter 2
p3_prev
REAL
Previous value of parameter 3
p4_prev
REAL
Previous value of parameter 4
p5_prev
REAL
Previous value of parameter 5
p6_prev
REAL
Previous value of parameter 6