Emerson Rosemount X-Stream Series, Инструкция по эксплуатации

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Emerson Process Management GmbH & Co. OHG
7-55
X-STREAM XE
Instruction Manual
HASXEE-IM-HS
10/2012
7
Maintenance & Procedures
In consequence of its design the sensor‘s
lifetime is limited and depends on theoretical
designed life and
O
xygen concentration. The
sensor output can be taken as a rough cri
-
terion 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 flushing with nitrogen
(N
2
) for less than 1 h (e.g. for analyzer zero
-
ing purpose) has no influence on measuring
characteristics.
For replacing the electrochemical sensor the
following tools are required:
• Philips screw drivers # 0 & 2
•
1 digital volt meter (measuring range
0 ... 2 V dc minimum) with suitable cables
and probes.
designed life (% hours)
O
2
concentration (%)
Lifetime =
Consider all applicable safety
instructions, especially those at
the beginning of this section 7.5!
7.6 Replacing Worn Out Sensors