En
gl
is
h (
G
B)
32
Fig. 42
T
n
too small
•
The controlled variable reaches the setpoint very
slowly:
– The reset time T
n
is too large.
Fig. 43
T
n
too large
•
The controlled variable exceeds the setpoint and
then reaches it very slowly:
– The proportional band X
p
is too small.
Fig. 44
X
p
too small
•
The controlled variable reaches the setpoint very
slowly or with a jump:
– The proportional band X
p
is too large.
Fig. 45
X
p
too large
15.1.6 Control modes for dosing applications
Proportional control
The purpose is to chlorinate a flow of water
uniformly.
Fig. 46
Chlorine dosing
If the water quality is constant, it is not necessary to
check the result as a specific quantity of dosed
chlorine results in a specific excess of chlorine.
Therefore this is an open-loop control. If the flow of
water is constant, an open-loop control is
unnecessary as the gas dosing unit is simply set to
the required dosing quantity.
However, this is not possible if the flow of water
varies. Then you must control the dosed quantity
according to the amount of flowing water:
TM
03
70
98
16
13
TM0
3
709
9
1
6
1
3
TM0
3
710
0
1
6
1
3
SP
t
Manipulated variable
Time
SP
t
Manipulated variable
Time
SP
t
Manipulated variable
Time
TM
03
71
01
16
13
TM
03
71
02
16
13
Pos.
Description
1
Water flow
2
Quantity of dosed chlorine
SP
t
Manipulated variable
Time
t
1
2