Evoqua WALLACE & TIERNAN SFC, Original Instruction Manual

Page: 78 / 288

78
WT.050.590.000.DE.IM.0719
Functions
SFC
4.
Special Functions
• The control direction can be switched.
• Automatic determination of the control parameter using the
integrated fuzzy module. The fuzzy module determines the
control parameter from the embedded Tconst and Tvar
process times.
• The setpoint can be switched between internal and external
• Ypi stop function during a change in control variable
• Control variable Wq available optionally as proportional or
indirect proportional as well as factor adjustment
• Smooth switch from compound loop to single feed forward or
single feedback closed-loop control via digital input 1, 2 or 3
available
Yout = Wq x (DF
Wq
+ ek x Kp x (1 + t/tn)) x Yout factor
Ratio Feedback control
t Internal controller cycle time
tn Integral action time
Kp Control amplification 100 / Xp
ek Setpoint-actual value
DF
Wq
Learned dosing factor for the current flow rate
Wq Flow rate signal in %
Yout Determined controller output value %
Yout factor This factor gives the option of increasing the dosing
output by a dosing factor DF of 100% when the setpoint
value is not reached increase the dosing output.
Setting range: 1.0– 4.0
Factory setting: 1.0
Please note
If the Yout factor is increased to >1, there is a danger that the
setpoint value will also not be reached with a higher flow rate
value, because the Yout value takes the value 100 % prematurely.
Determining the
compound loop process times
To adjust the control for compound loop, the Tconst and Tvar
process times must bet entered in the parameter menu path.
These times refer to control loop dead times,which on the one
hand are independent of the control variables, and on the other
hand depend proportionally on the control variables.
The constant dead time< Tconst > (independent of control
variable) consists of the control variable measurement dead time
(measuring dead time) and possible dosing delays.
The variable dead time< Tvar > depends on the current control
variable and is entered in the menu at a control variable of 100%.
The following calculation examples apply to the use of the SFC for
flow-controlled chlorine dosing with chlorine overfeed correction
(potable water control loop).