Description
Original instructions
Function description
The function block RATIO carries out ratio control when it is attached to a controller.
The aim of ratio control is to establish a ratio of one process variable PV (controlled variable) to another PV_TRACK (reference variable). The role of the RATIO function block is to calculate the Control setpoint corresponding to the control variable.
EN and ENO can be configured as additional parameters.
Properties
The function block contains the following properties:
Formula
Calculation of the control setpoint
Representation in FBD
Representation:
Representation in LD
Representation:
Representation in IL
Representation:
CAL RATIO_Instance (PV:=ProcessVariable, 
    PV_TRACK:=ControllingProcessVariable, 
    RK:=ExternalRatioCoefficient, 
    K_RK:=CoefficientTypeFlag, K:=InternalRatioCoefficient, 
    PARA:=Parameters, KACT=>RealRatioCoefficient, 
    SP=>CalculatedOutput, STATUS=>StatusWord)
Representation in ST
Representation:
RATIO_Instance (PV:=ProcessVariable, 
    PV_TRACK:=ControllingProcessVariable, 
    RK:=ExternalRatioCoefficient, 
    K_RK:=CoefficientTypeFlag, K:=InternalRatioCoefficient, 
    PARA:=Parameters, KACT=>RealRatioCoefficient, 
    SP=>CalculatedOutput, STATUS=>StatusWord) ;
Parameter description RATIO
Input parameter description:
Parameter
Data type
Meaning
PV
Process value regulated by the control loop (only used to calculate KACT)
PV_TRACK
REAL
Reference variable of the control loop
RK
REAL
Remote relationship coefficient
K_RK
Coefficient type for ratio used
"1": remote ratio RK
"0": local ratio K
K
REAL
Coefficient for local ratio
PARA
Parameter
Output parameter description:
Parameter
Data type
Meaning
KACT
REAL
Coefficient for real ratio
SP
REAL
Calculated output
STATUS
Status word
Parameter description Para_RATIO
Data structure description
Element
Data type
Meaning
k_min
Lower threshold with K or RK
k_max
REAL
Upper threshold with K or RK
sp_min
REAL
Lower threshold of the calculated output SP
sp_max
REAL
Upper threshold of the calculated output SP
bias
REAL
Offset coefficient