Evoqua WALLACE & TIERNAN MFC, Instruction Manual

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WT.050.580.000.DE.IM.0714
Functions
MFC
4.
How the compound-loop-control
works
The compound-loop-controller outputs a dosing rate proportional
to the flow rate, which does not have a fixed dosing factor
proportional to the flow rate as in the single feed forward control,
but varies depending on demand.
To detect control deviations, the sensor module 1 records the
control variable and a setpoint is specified, which are compared
with the integrated single feed back control.
The internal setpoint can be set within the measuring range of
sensor module 1. "Setpoint Source" must be set to "internal". An
external setpoint from 0–100 % can be provided via the mA/V input
signal. "Setpoint Source" must be set to "external". You can switch
between internal and external setpoint via the digital input. The
"Setpoint Source" must be set to "external with DI3" or "internal
with DI3".
The Xp and Tn control parameters of this higher-level single feed
back control are automatically determined by the integrated fuzzy
logic Tconst and Tvar process times to be entered at 100 % flow
rate. Because the Tvar process time changes, Tvar, Xp and Tn are
continuously updated by the integrated fuzzy logic.
The MFC operates internally with a dosing factor table for 0–105 %
flow. In 5 % intervals, the device determines the required dosing
factors automatically during operation based on the corresponding
flow rate.. The single feed back control corrections are transferred
into the dosing factor table during this process. Non-linearities in
the control loop are learned this way. This quickly activates the
setpoint if flow rate changes occur.
The control operating mode can be switched between single feed
forward control and single feed back control via digital input.
The control direction can be selected with the parameter "Control
Direction" = direct or inverse (e.g. direct = chlorination, inverse =
dechlorination)