8
Controller configuration
The possible controller settings are determined
by the equipment incorporated in your
instrument as well as by the preliminary
settings made in the menu system set-up /
output relays« (see chapter 7.1.3).
Note:
For two-circuit instruments, limit
value and controller always relate
to input 1.
8.1
Types of controller
The Mycom CPM 152 measuring transmitter
has the following controller functions for
controlling the pH value:
• Limit contacts
• P, PI, PD, PID controllers
• Neutralisation controllers (P, PI, PD, PID
controller for 2 control contacts)
• Two-range P controller
• Three-level step controller
Limit contactor
Depending on the measured value in each
case, the contact concerned is either
permanently closed or permanently open.
Hysteresis and switching function (min./max.)
parameters can be set.
PID controllers
There is a choice of conventional P, PI, PD
and PID controllers available in the controllers
menu for pH/redox controlling with an
actuator. Control contact 1 is used to output
the actuating signal. Setting of the parameters
of the PID controllers is via the values control
gain K, integral action time T
n
and derivative
action time T
v
.
Direct controller action:
pos. control deviation X
w
➔
pos. act. signal
Inverse controller action:
neg. control deviation X
w
➔
pos. act. signal
X
w
= X – W, X = measured value,
W = specified value, Y = actuating signal
Neutralisation controllers
In the neutralisation control process, the
pH level of a medium is kept constant by the
addition of acid or alkaline solution.
Two separate actuating signals are required
for this purpose, one for acid metering and
one for alkaline solution metering.
The neutralisation controller is a controller
with 2 control contacts that has been
specially designed for this assignment.
P, PI, PD and PID are available as possible
control structures.
The control gain for alkaline solution and acid
can be set separately.
Integral action time T
n
and derivative action
time T
v
are valid for both actuators.
Within the »neutral zone« there is no metering
of alkaline solution or acid (Y = 0) for
controllers without integral portion (P, PD) and
constant metering of alkaline solution or acid
(Y
new
= Y
old
) for controllers with integral
portion (PI, PID).
pH / mV
pH / mV
100 %
50 %
100 %
50 %
Limit
Limit
Hysteresis
Hysteresis
DIAGR_2.CDR
Y
h
MIN function
MAX function
Y
h
Fig. 8.1
Control curve of a limit
contactor
X
X
w
w
100 %
100 %
K
p
p
K
Y
Y
1
1
direct
inverse
DIAGR_1.CDR
Fig. 8.2
Control curve of a
proportional controller
with direct and inverse
function
100 %
Xw
50 %
Y
1
1
DIAGR_1A.CDR
control contact 2
(for acid)
neutral
zone
control contact 1
(for alkaline solution)
neutral
zone
G
alkal.
G
acid
Fig. 8.3
Control curve of a
proportionally acting
neutralisation controller
Controller configuration
mycom CPM 152
48
Hauser
