Evoqua WALLACE & TIERNAN MFC, Instruction Manual

Page: 86 / 268

86
WT.050.580.000.DE.IM.0714
Functions
MFC
4.
Calculation 3:
The sample water distraction is carried out as in calculation 1 and/
or 2. To increase the exposure time, the sample water is also sent
through a delay tank.
The exposure time in the delay tank must be added to the
calculated time.
Determining the dosing dead
time (dosing delay)
Dosing dead times arise from long dosing lines and positioner
running times.
Calculation 1:
Determining the dead time based on dosing line length
The dosing dead time can be determined as follows:
t
dos
= (4.71 x d
dos
x d
dos
x l
dos
) : Q
dos
(result in min)
d
dos
= Internal diameter of the dosing line in cm
l
dos
= Length of the dosing line in m
Q
dos
= Dosing line flow rate in l/h
Calculation 2:
If rapid control variable changes are expected in the system, which
the dosing equipment cannot adjust to (e.g. positioner running
times, dosing pump cycle times), the dosing delay time should be
assumed under all circumstances to be half of the positioner
running time ty or the cycle time tp.
At a positioner running time of 80 seconds, a value of approx. 40 s
should be assumed as the constant dosing delay.
The sum of the measured dead time and the dosing delay is
displayed in the< Tconst > menu in minutes.
Determining the control variable
dependent Tvar dead time
The control variable dependent Tvar dead time depends on the
nominal flow rate, the internal diameter of the line and the distance
between where the chlorine is added and the sample water
extracted.
t
var
= (d
pipe
x d
pipe
x l
pipe
) : (212.3 x Q
nom
) (result in min)
d
pipe
= Internal diameter of the pipeline in cm
l
pipe
= Distance between where chlorine is added and sample
water extracted in m
Q
nom
= Nominal flow rate in m³/h (reflects the flow rate,
which is preset for the controller as 100% flow signal
If there are special reaction tanks in the system, they must be
treated separately.