Description
Original instructions
Function description
This function block is suitable for simple three-point step-action controls.
Control of the actuator proceeds according to the direction of the actual/setpoint value deviation in relation to the upper and lower threshold value. The control of the threshold value describes a configurable hysteresis.
This controller can also be used for temperature regulation. A traditional controller (such as a PI_B controller), which a function block such as the PWM1 should be switched to is preferable for complex regulation.
EN and ENO can be configured as additional parameters.
Properties
The control block has the following properties:
Representation in FBD
Representation:
Representation in LD
Representation:
Representation in IL
Representation:
CAL STEP3_Instance (PV:=ProcessValue, SP:=SetPoint,  
    MAN_AUTO:=OperatingMode, PARA:=Parameters, 
    OUT_NEG=>LogicOutputNegativ, 
    OUT_POS=>LogicOutputPositiv, DEV=>Deviation, 
    MA_O=>CurrentOperatingMode, STATUS=>StatusWord)
Representation in ST
Representation:
STEP3_Instance (PV:=ProcessValue, SP:=SetPoint,  
    MAN_AUTO:=OperatingMode, PARA:=Parameters, 
    OUT_NEG=>LogicOutputNegativ, 
    OUT_POS=>LogicOutputPositiv, DEV=>Deviation, 
    MA_O=>CurrentOperatingMode, STATUS=>StatusWord) ;
Parameter description STEP3
Input parameter description:
Parameter
Data type
Meaning
PV
Process value
SP
REAL
Setpoint
MAN_AUTO
Controller operating mode:
"1" : Automatic mode
"0" : Halt mode
PARA
Parameter
Output parameter description:
Parameter
Data type
Meaning
OUT_NEG
BOOL
Logical output: is set to 1 for negative deviations
OUT_POS
BOOL
Logical output: is set to 1 for positive deviations
DEV
REAL
Deviation (PV-SP)
MA_O
BOOL
Current operating mode of the function block
(0: Halt, 1: Automatic)
STATUS
Status word
Parameter description Para_STEP3
Data structure description
Element
Data type
Meaning
dev_ll
Lower deviation threshold (≤ 0)
dev_hl
REAL
Upper deviation threshold (≤ 0)
hyst
REAL
Hysteresis
pv_inf
REAL
Lower limit of the process value range
pv_sup
REAL
Upper limit of the process value range