Instruction manual

NGA 2000 MLT Hardware
MEASURING PRINCIPLE
2 - 11
Emerson Process Management GmbH & Co. OHG
Instruction Manual
90002929
07/2006
2.3.2 Electrochemical Measurement (EO
2
)
This sensor uses the principle of galvanic cells, fig. 2-5 shows the design.
Fig. 2-5: Structure of electrochemical Oxygen Sensor
The electrochemical oxygen sensor‘s key components are a lead anode (1) and a gold cathode
(2) surrounded by a special acid electrolyte (3).
The gold electrode is integrated solid with the membrane,which is a non-porous fluororesin
membrane. Oxygen which barely diffuses through the membrane is electrochemically reduced on
the gold electrode.
The temperature compensating thermistor and adjusting resistance are connected between the
cathode and anode. The current generated by oxygen reduction is converted into a voltage by
these resistances.
The value of the current flowing to the thermistor and resistance varies in proportion to the oxygen
concentration of the measuring gases which contact the membrane. Therefore, the voltage at the
terminal of the resistances is used for the sensor output to measure the oxygen concentration.
OXYGEN MEASUREMENT
12
9
8
4
10
1
6
5
7
3
11
2
12
11
13