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Emerson Process Management GmbH & Co. OHG 7-41
X-STREAM XE
Instruction Manual
HASXEE-IM-HS
10/2010
7
Maintenance & Procedures
7.5 Replacing the Electrochemical Sensor
7.5 Replacing the Electrochemical 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
criterion for end of lifetime: The sensor is
worn-out when the output in atmosphere is
below 70 % of the initial output. The period
till then 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 therefore calcu-
lated to approx. 42,857 hrs, corresponding
to approx. 5 years.
Irrespective of all calculations above:
A sensor is worn-out when, connected to
ambient air, the output voltage is less than
2.8 V: Replace the sensor!
Note 1!
The given lifetime values are for reference
only! The expected lifetime is greatly affec-
ted 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 de-
creases in oxygen concentration. (Operation
at 40 °C halves lifetime).
Note 2!
Due to the measuring principle the electro-
chemical oxygen cell requires a minimum
internal consumption of oxygen (residual
humidity avoids drying up the cell). Supplying
cells continuously with dry sample gas of low
grade oxygen concentration or with sample
gas free of oxygen could result in a reversible
detuning of O
2
sensitivity. The output signal
will become unstable, but response time re-
mains constant.
For proper measurement results the cell
needs to be supplied continuously with con-
centrations of at least 0.1 Vol.-% O
2
.
We recommend using the cell if need be in
alternating mode, means to purge the cell with
conditioned ambient air (not dried, but dust
removed) when measurement pauses.
If it is necessary to interrupt the oxygen sup-
ply for several hours or days, the cell has to
regenerate (supply cell for about one day with
ambient air). Temporary ushing with nitrogen
(N
2
) for less than 1 h (e.g. for analyzer zero-
ing purpose) has no inuence on measuring
characteristics.
For replacing the electrochemical sensor the
following tools are required:
• Philips screw drivers # 0 & 2
• Square key for the eld housing's squash
fasteners
• allen key for the ameproof analyzer to
remove/open the cover/front door.
• 1 digital volt meter (measuring range
0 ... 2 V dc minimum) with suitable cables
and probes.
designed life (% hours)
O
2
concentration (%)
Lifetime =