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Emerson Process Management GmbH & Co. OHG 3-9
X-STREAM X2
Instruction Manual
HASX2E-IM-HS
02/2012
3
Measuring Principles
3.2 Oxygen Measurement
Fig. 3-7: Electrochemical reaction of Oxygen Sensor
Resistance (6)
Thermistor (5)
(11)
(red) (black)
(+)
Lead
anode (1)
(-)
Gold
cathode (2)
Electrochemical reaction:
Electrolyte (3)
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.