bürkert 8205 Bedienungsanleitung Seite 54

2 SPECIFICATION
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 15-30 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 or transistors.
Controlling Principle
The pH controller 8205 is designed for use
in static or dynamic process of pH control.
The output signals may control a valve or a
pump, by means of impulses which time
duration or frequency is computed
according to user parameters and pH value
of the fluid.
(See § 4.3 Operation).
Refer to Appendix A for general
characteristics of PID controllers.
PH CONTROLLER 8205
ACID BASE
Fig. 2.1
Static process control
A) Static process: Fluid controlled in a
tank, without significant flow, the control
mode is proportional.
ACID BASE
Dynamic process control
Fig. 2.2
B) Dynamic process: Fluid controlled in a
pipe, or in a tank with significant flow. The
control mode is PI or PID.
E-4-
ALARM
ALARM