Evoqua WALLACE & TIERNAN MFC, Instruction Manual

Page: 89 / 268

MFC
Functions
4.
89
A second measurement (sensor measuring module 2 or measured
value obtained with CAN interface) is used to optimise the control
and it detects possible control deviations, which, for example,
arise as a result of attrition in a delay tank. The compound-loop-
control's adaptive setpoint adjustment then optimises the setpoint,
in order to eliminate existing control deviations.
The setpoint adjustment operates with a delay time that
determines the setpoint trim function Tconst and Tvar as well as
the flow rate using the process times. The flow must be constant
during this delay, otherwise the time restarts.
Behavior in operation Setpoint 1 = Compound-loop-control setpoint from module
slot 1
Actual value 1 = Measured value from module slot 1
Setpoint 2
= Setpoint trim function setpoint from module
slot 2
Actual value 2 = Measured value from module slot 2
The compound-loop-control of the measurement from module 1
controls the set setpoint 1 depending on the flow rate (see 4.5.3
“Compound-Loop-Control" on page 81). The setpoint has been
reached if the actual value 1 is less that 5 % away from the
measuring range of setpoint 1.
For example:
Setpoint 1 = 0.50 mg/l
Measuring range 1.00 mg/l
5 % of measuring range = 0,05 mg/l =>"good range" =
0.45–0.55 mg/l
A delay time begins when the setpoint 1 is reached, after which the
setpoint trim function is activated. This delay time depends on the
Tconst. and Tvar delay times and the current flow rate. The smaller
the flow rate, the longer the delay time.
Example:
Flow rate = 50 %
Tvar (at 100 % flow rate) = 2h:30min
Tconst = 2 min
=> Delay = 100 % / 50 % x Tvar + Tconst = 5h:02min
The setpoint trim compares setpoint2 with actual value2 once the
time has expired and changes the compound-loop-control
setpoint1 according to the following equation, if necessary:
New setpoint1 = set (setpoint2 - actual value2) x trim factor
If the flow rate changes, the delay time is reset.
The delay time is also restarted if the actual value1 is more than
5 % of the setpoint 1. The time starts again only after the 5 %
range has been reached.
The delay time is always reset after an automatic setpoint change
and only restarted once the setpoint range has been reached.