Description
Original instructions
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Function description
The function block replicates a three-point step controller, and exhibits a PD-like behavior due to a dynamic feedback path.
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.
EN and ENO can be configured as additional parameters.
Properties
The function block THREE_STEP_CON1 has the following properties:
Representation in FBD
Representation:
Representation in LD
Representation:
Representation in IL
Representation: 
CAL THREE_STEP_CON1_Instance (R:=ResetMode, 
    SP:=SetPointInput, PV:=ProcessVariable, 
    GAIN:=ProportionalRate, TI:=ResetTime,    
    T_PROC:=NominalControllerTime, HYS:=Hysteresis, 
    DB:=Deadband, Y_POS=>PosControlVarAt_ERR_EFF, 
    Y_NEG=>NegControlVarAt_ERR_EFF, 
    ERR_EFF=>EffectiveError)
Representation in ST
Representation: 
THREE_STEP_CON1_Instance (R:=ResetMode, 
    SP:=SetPointInput, PV:=ProcessVariable, 
    GAIN:=ProportionalRate, TI:=ResetTime,    
    T_PROC:=NominalControllerTime, HYS:=Hysteresis, 
    DB:=Deadband, Y_POS=>PosControlVarAt_ERR_EFF, 
    Y_NEG=>NegControlVarAt_ERR_EFF, 
    ERR_EFF=>EffectiveError) ;
Parameter description
Description of input parameters:
Parameter
Data type
Description
R
BOOL
"1": Reset mode
SP
REAL
Setpoint input
PV
REAL
Actual value input
GAIN
REAL
Proportional action coefficient (gain)
TI
TIME
Integral time
T_PROC
TIME
Nominal actuating time of the controlled valve
HYS
REAL
Hysteresis from three point switch
DB
REAL
Dead zone
Description of output parameters:
Parameter
Data type
Description
ERR_EFF
REAL
Effective switch value
Y_POS
BOOL
"1" = positive manipulated variable at output ERR_EFF
Y_NEG
BOOL
"1" = negative manipulated variable at output ERR_EFF
Runtime error
With HYS > 2 * DB an error message is returned.
NOTE: For a list of all block error codes and values, see CLC.
Warning
In the following cases a warning will be returned:
If...
Then...
GAIN ≤ 0
the controller operates without feedback.
TI = 0
the controller operates without feedback.
T_PROC = 0
the controller operates with a predetermined value of T_PROC = 60 s.
NOTE: For a list of all block error codes and values, see CLC.