Description

Function description

The function block PI_B depicts a PI-algorithm with a mixed structure (series/parallel). Its functions derive from function block PIDFF. These functions enable the function block to perform most classical control applications, without compromising user friendliness or using too many system resources. However, for difficult control tasks requiring extended control functions, the PIDFF block should be used.

and can be configured as additional parameters.

Functions

The most important functions of function block PI_B are as follows:

Calculation of the proportional and integral component in incremental form
Actual value, setpoint value, and default value in physical units
Direct or inverse action
Possibility of upgrading a block-external I component (RCPY input)
Dead zone on deviation
Incremental value and absolute value default
Upper and lower limit value of the default signal
Output offset
Selecting manual/automatic mode
Tracking mode
Upper and lower limit of the setpoint value

Extended functions

As is the case with PIDFF these functions can be extended by using various additional function blocks:

Automatic control setting via the block AUTOTUNE
Internal or external setpoint value selection via the block SP_SEL
Controlling manual operation of the sampled servoloops using the function block MS

Representation in FBD

Representation:

Representation in LD

Representation:

Representation in IL

Representation:

CAL PI_B_Instance (PV:=ProcessValue, SP:=SetPoint,
    RCPY:=CopyOfRealAction, MAN_AUTO:=OperatingModeFlag,
    PARA:=Parameters, TR_I:=InitializationInput,
    TR_S:=InitializationOrder, OUT:=AbsoluteOutput,
    OUTD=>IncrementalOutput,
    MA_O=>CurrentBlockOperatingMode, DEV=>ValueOfDeviation,
    STATUS=>StatusWord)

Representation in ST

Representation:

PI_B_Instance (PV:=ProcessValue, SP:=SetPoint,
    RCPY:=CopyOfRealAction, MAN_AUTO:=OperatingModeFlag,
    PARA:=Parameters, TR_I:=InitializationInput,
    TR_S:=InitializationOrder, OUT:=AbsoluteOutput,
    OUTD=>IncrementalOutput,
    MA_O=>CurrentBlockOperatingMode, DEV=>ValueOfDeviation,
    STATUS=>StatusWord) ;

Parameter description PI_B

CAUTION

UNEXPECTED BEHAVIOR OF APPLICATION

Do not set the datatype of the PARA input parameter to constant, in the general attributes tab of the Data Properties window.

Failure to follow these instructions can result in injury or equipment damage.

Input parameter description:

Parameter	Data type	Meaning
PV	REAL	Process value
SP	REAL	Setpoint
RCPY	REAL	Copy of the effective actuator position
MAN_AUTO	BOOL	Controller operating mode: "1" : Automatic mode "0" : Manual mode
PARA	Para_PI_B	Parameter
TR_I	REAL	Initialization input
TR_S	BOOL	Initialization command

Input / output parameter description:

Parameter	Data type	Meaning
OUT	REAL	Actuator output

Output parameter description:

Parameter	Data type	Meaning
OUTD	REAL	Differential output Difference between the output of the current and previous execution
MA_O	BOOL	Current operating mode of the function block: "1": Automatic operating mode "0": other operation mode (i.e. manual or tracking mode)
DEV	REAL	Deviation value (PV - SP)
STATUS	WORD	Status word

Parameter description Para_PI_B

Data structure description

Element	Data type	Meaning
id	UINT	Reserved for autotuning
pv_inf	REAL	Lower limit of the process value range
pv_sup	REAL	Upper limit of the process value range
out_inf	REAL	Lower limit of the output value range
out_sup	REAL	Upper limit of the output value range
rev_dir	BOOL	"0": direct action of the PID controller "1": opposite action of the PID controller
en_rcpy	BOOL	"1": the RCPY input is used
kp	REAL	Proportional contribution (gain)
ti	TIME	Integral time
dband	REAL	Dead zone on deviation
outbias	REAL	Manual adjustment of static deviation

Base	Lower limit	Upper limit
Hexadecimal	16#0	16#FFFF
Octal	8#0	8#177777
Binary	2#0	2#1111111111111111

Data	Representation in one of the bases
0000000011010011	16#D3
1010101010101010	8#125252
0000000011010011	2#11010011

REAL

The REAL type is encoded in a 32 bit format.

The possible value ranges are shown in the figure below:

When a result is:

between -1,175494e-38 and 1,175494e-38, it is considered to be a DEN;
less than -3.402824e+38, the symbol -INF (for - infinity) is displayed;
greater than +3.402824e+38, the symbol INF (for + infinity) is displayed;
undefined (square root of a negative number), the symbolNAN is displayed.

NOTE: The IEC 559 standard defines two classes of NAN: the silent NAN (QNAN) and the signaling NAN (SNAN). A QNAN is a NAN with a most significant fraction bit while an SNAN is a NAN without a most significant fraction bit (bit number 22). QNANs can be propagated via most arithmetic operations without throwing an exception. As for SNANs, they generally indicate n invalid operation when they are used as operands in arithmetic operations (see %SW17 and %S18).

NOTE: When a DEN (non-standardized number) is used as an operand, the result is not significant.