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3-12
Instruction Manual
HASAxE-IM-HS
05/2006
Emerson Process Management GmbH & Co. OHG
3-2 Oxygen Measurement
Resistance (6)
Thermistor (5)
(11)
(red) (black)
(+)
Lead
anode (1)
(-)
Gold
cathode (2)
Electrochemical reaction: O
2
+ 2 Pb 2 PbO
Electrolyte (3)
2 Pb + 2 H
2
O 2 PbO + 4 H
+
+ 4 e
-
O
2
+ 4 H
+
+ 4 e
-
2 H
2
O
Fig. 3-8: Electrochemical reaction of Oxygen Sensor
Note!
The given values are for reference only! The
expected lifetime is greatly affected by the
temperature of the environment in which the
sensor is used or stored. Increases or
decreases in atmospheric pressure have the
same effect as that by increases or decreases
in oxygen concentration (Operation at 40 °C
halves lifetime).
In consequence of it‘s design the sensor‘s
lifetime is limited and depends on theoretical
designed life and oxygen concentration. The
sensor output can be taken as a rough criterion
for end of lifetime: The sensor is weared when
the output in atmosphere is below 70 % of the
initial output. The period till this can be
calculated by
The sensor‘s designed life under constant
conditions of 20 °C is approx. 900,000 hrs.
The lifetime at 21 % oxygen is then calculated
to approx. 42,857 hrs, corresponding to
approx. 5 years.
designed life (hours)
O
2
concentration (%)
Lifetime =
⎝