Description

Function description

The function block represents a complex PID controller that in its design specifically includes cascade treatment. The control structure is displayed in theStructure diagram.

NOTE: This function block performs an internal initialization in the first program cycle after a warm start or cold start (e.g. application download or power cycle) of the PLC program.

Due to this, you have to make sure that the function block is invoked in the first program cycle. In case of inkoving the function block in a later program cycle, the internal initialization will not be performed and the ouputs may deliver wrong values.

WARNING

UNEXPECTED OUTPUT BEHAVIOUR

Make sure that the function block is always invoked in the first program cycle.

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

and can be configured as additional parameters.

Properties

The function block has the following properties:

real PID controller with independent gain, ti, td setting
Manual, halt, automatic, cascade, reset, manual value operating modes tracking
Velocity limit for manual operation
Adjustable manual manipulated value tracking
Velocity limit for reference variable
bumpless changeover between manual and automatic
Manipulated variable limiting
bumpless, individually connectable P, I and D components
bumpless gain modification
Choice of anti-windup reset and anti-windup halt
Displacement of anti-windup limits compared to control limits
Anti-windup measure with an active I component only
definable delay of the D component
D component connectable to controlled variable PV or system deviation ERR
Dead zone with gain reduction
external operating point (in P, PD and D operation)
Choice of bump/bumpless manual/automatic switchover

Transfer function

The transfer function is:

Explanation of the variables:

Variable	Description
YD	D component (only when en_d = 1)
YI	I component (only when en_i= 1)
YP	P component (only when en_p= 1)

Representation in FBD

Representation:

Representation in LD

Representation:

Representation in IL

Representation:

CAL COMP_PID_Instance (SP:=ReferenceVariable, 
    PV:=ControlledVariable, 
    SP_CAS:=CascadeReferenceVariable, MODE:=OperatingModes, 
    PARA:=Parameters, YMAN:=ManuallyManipulatedValue, 
    YRESET:=Y_ResetValue, FEED_FWD:=DisturbanceInput, 
    OFF:=OffsetFor_P_PD_Operation, Y:=ManipulatedVariable, 
    SP_CAS_N:=CascadeReferenceVariable,
    YMAN_N:=ManuallyManipulatedValue,
    OFF_N:=OffsetFor_P_PD_Operation, ERR=>SystemDeviation,
    STATUS=>OutputStatus)

Representation in ST

Representation:

COMP_PID_Instance (SP:=ReferenceVariable, 
    PV:=ControlledVariable, 
    SP_CAS:=CascadeReferenceVariable, MODE:=OperatingModes, 
    PARA:=Parameters, YMAN:=ManuallyManipulatedValue, 
    YRESET:=Y_ResetValue, FEED_FWD:=DisturbanceInput, 
    OFF:=OffsetFor_P_PD_Operation, Y:=ManipulatedVariable, 
    OFF_N:=OffsetFor_P_PD_Operation, ERR=>SystemDeviation,
    STATUS=>OutputStatus) ;

Parameter description COMP_PID

Description of the input parameters:

Parameter	Data type	Description
SP	REAL	Reference variable
PV	REAL	Controlled variable
SP_CAS	REAL	Cascade reference variable
MODE	Mode_COMP_PID	Operating mode
PARA	Para_COMP_PID	Parameter
YMAN	REAL	Manually manipulated value
YRESET	REAL	Manipulated variable reset value
FEED_FWD	REAL	Disturbance input
OFF	REAL	Offset for P/PD operation

Description of input / output parameters:

Parameters	Data type	Meaning
Y	REAL	Manipulated variable
SP_CAS_N	REAL	Cascade reference variable
YMAN_N	REAL	Manually manipulated value
OFF_N	REAL	Offset for P/PD operation

Description of the output parameters:

Parameters	Data type	Description
ERR	REAL	System deviation
STATUS	Stat_COMP_PID	Output status

Parameter description Mode_COMP_PID

Data structure description

Element	Data type	Description
r	BOOL	"1": Reset mode
man	BOOL	"1": Manual mode
halt	BOOL	"1": Halt mode
cascade	BOOL	"1": Cascade mode
en_p	BOOL	"1": P component on
en_i	BOOL	"1": I component on
en_d	BOOL	"1": D component
d_on_pv	BOOL	"1": D component on controlled variable "0": D component on system deviation
halt_aw	BOOL	"1": Anti-windup Halt "0": Anti-windup reset
bump	BOOL	"0": Bumpless operating mode switchover
ymanc	BOOL	"1": YMAN tracking

Parameter description Para_COMP_PID

Data structure description

Element	Data type	Description
gain	REAL	Proportional action coefficient (gain)
ti	TIME	Integral time
td	TIME	Derivative time
td_lag	TIME	D component delay time
db	REAL	Dead zone
gain_red	REAL	Gain reduction in dead zone (db)
rate_sp	REAL	Setpoint velocity (SP) [1/s]
rate_man	REAL	Manually manipulated velocity value (YMAN) [1/s]
ymax	REAL	Upper threshold for Y
ymin	REAL	Lower threshold for Y
delt_aw	REAL	Limit expansion for anti-windup

Parameter description Stat_COMP_PID

Data structure description

Element	Data type	Description
st_r	BOOL	"1": COMP_PID is in reset mode
st_man	BOOL	"1": COMP_PID is in manual mode
st_halt	BOOL	"1": COMP_PID is in halt mode
st_auto	BOOL	"1": COMP_PID is in automatic mode
st_cascade	BOOL	"1": COMP_PID is in cascade mode
st_max	BOOL	"1": Y ≥ Para_COMP_PID.ymax
st_min	BOOL	"1": Y ≤ Para_COMP_PID.ymin

Runtime error

An error message is returned if

an unauthorized floating point number is placed at the input PV
gain_red > 1 or gain_red < is 0
db < is 0
ymax < is ymin

NOTE: For a list of all block error codes and values, see CLC_PRO.