8205
E-5-
pH CONTROLLER 8205
2 SPECIFICATION
WASTE WATER
WASTE WATER
ACID
BASE
ACID
BASE
pH 7
Measuring Principle
The most important part of a pH electrode
is the glass membrane of pH-selective glass.
When the electrode is immersed into the
solution, an electrical charge caused by H-
ions (H
+
) generates a cell voltage between
the glass membrane and the solution. This
electric voltage is recorded with reference
to a reference electrode, located around the
pH glass electrode. The cell voltage of the
combination electrode is directly
proportional to the pH value (59.16 mV per
pH unit at 25
°
C).
The controller functions in a 3-wire circuit
and requires a power supply of 12...30 VDC.
A relay alarm contact, and a 4...20 mA
standard signal proportional to the pH or to
the T
°
C, are available as output signals.
The pulse output signals are provided by
relays (standard); triacs or transistors .
Controlling Principle
The pH controller type 8205 is designed for
use in static or dynamic process of pH
control. The output signals control a valve
(e.g.: Bürkert Type 2031) or a pump, by
means of impulses which times duration or
frequency is computed according to users
parameters and pH value of the fluid.
(See § 4.3 Operation).
A) Static process: Fluid controlled in a tank,
without significant flow, the control mode
is proportional.
B) Dynamic process: Fluid controlled in a
pipe, or in a tank with significant flow. The
control mode is PI or PID.
Fig. 2.2 Dynamic process control
The pH sensor type 8200 for pH controller
type 8205 separate version can be easily
installed into pipes using our specially
designed fitting system. Please refer to the
pH sensor type 8200 instruction manual
(Ref 428937J).
pH 7
Fig. 2.1 Static process control
Refer to Appendix A for general
characteristics of PID controllers.
