6 Start-up
Mycom S CPM 153
58
Hauser
Fig. 20:
Schematic diagram of the CPM 153controller with K
R
(X) as the total gain
Range-dependent modulation gain
The majority of pH neutralisation processes are strongly non-linear (Example: titration
curve). If you specify a strong alkali in portions to a fixed volume of a weak acid, the pH
value changes. The change in pH value is, at the beginning, relatively small, larger in
the area of the so-called equivalence point and then ever smaller.
In the following diagram, such a titration curve is represented for a weak acid with a
strong alkali (y axis: pH value, x axis: volume units added to a strong alkali).
Fig. 21:
Schematic titration curve of a weak acid with a strong alkali.
For difficult neutralisations, the CPM 153 controller gives you the option of partial
compensating for the non-linearity by entering an inverse characteristic Y(X).
X
Actual value
W
Set point
E
Control difference
Y
Set value
K
R
Modulation gain (total gain)
T
n
Integral action time (I component)
T
v
Derivative action time (D component)
X
W
E
Y
I
P
D
K (X)
R
*
T *S
v
1/(T *S)
n
1
+
+
+
–
+
C07-CPM153xx-05-06-xx-xx-001.eps
pH
X [ml NaOH]
5
6
7
8
9
10
11
12
5
10
15
20
25
30
35
C07-CPM153xx-05-06-00-xx-008.EPS
