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Emerson Process Management GmbH & Co. OHG 3-9
X-STREAM XE
Instruction Manual
HASXEE-IM-HS
04/2010
3
Principles
3.2 Oxygen Measurement
Resistance (6)
Thermistor (5)
(11)
(red) (black)
(+)
Lead
anode (1)
(-)
Gold
cathode (2)
Electrochemical reaction:
Electrolyte (3)
Fig. 3-7: Electrochemical Reaction of Oxygen Sensor
In consequence of its 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 cri-
terion 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 lifetime under constant
conditions of ambient temperature 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.
An indicator for end of lifetime is a reduced
output signal. In this case the sensor must be
replaced to ensure accurate measurements
(
Chapter 7 "Maintenance").
designed life (% hours)
O
2
concentration (%)
Lifetime =
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 (operation at 40 °C
halves lifetime).
Increases or decreases in atmospheric pres-
sure have the same effect as increasing or
decreasing oxygen concentrations.