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AMU-II Oxytrace
Product Description
2.
2.1.
Application
Measuring
principle
Temperature
compensation
A-96.150.541 / 111223
Product Description
Description of the System
The AMU-II Oxytrace is used to measure low levels of oxygen in
high-purity water. Especially in power plant water cycles (e.g. feed-
water), a very low level of oxygen is needed to prevent corrosion.
Clark principle:
The sensor consists of one noble metal electrode (e.g. platinum or
gold), a reference electrode (mostly Ag/AgCl) and optionally a metal
guard electrode.
The Clark-type electrode is the most widely used oxygen sensor for
measuring oxygen dissolved in a liquid. The basic principle is that
there is a cathode and an anode submersed in an electrolyte and a
voltage is applied between the two parts. Oxygen enters the sensor
through a permeable membrane by diffusion, and is reduced at the
cathode according to
-
O
+ 4e
+ 2 H
O --> 4 OH
2
2
This reaction creates a measurable current. There is a linear correla-
tion between the oxygen concentration and the electrical current.
The guard electrode is on the same voltage level as the cathode but
there is no current measurement. Oxygen which diffuses from the
electrolyte to the cathode is consumed by the guard electrode. As a
consequence, residual oxygen in the electrolyte will no more disturb
the measurement signal and the response time to low oxygen levels
will be shorter.
The measuring signal depends on temperature, but is automatically
compensated to 25 °C. The sample temperature is determined con-
tinuously by a temperature sensor inside the oxygen electrode.
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9
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