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© Servomex Group Limited 2017
AquaXact Issue 1.0
4
Installation
Do not attempt to install, commission, maintain or use the AquaXact
1688 Dew Point Transmitter unless you are trained and know what you
are doing.
Follow the instructions in this section to safely install the AquaXact 1688
Dew Point Transmitter.
Do not install the unit in places subject to extreme mechanical vibration
or shock. If you do, sample measurements may not be accurate and the
transmitter may be damaged.
Sensor installation
4.1
The moisture content at the sensor is not only due to the moisture of the gas being
measured, but is also due to desorption of water from tubing, trapped moisture (at the
interconnection points, valves, filters and other hygroscopic materials in the system), leaks
in the system and others. As a result the measurement may vary from what is expected
and care should be taken in choosing the sampling approach utilized in the measurement.
Factors such as gas pressure, flow rate, materials of construction, length and diameter of
tubing, number of interconnecting fittings, dead space in tubing and manifolds will
influence the observed measurement value and response time.
The high-capacitance thin-film sensor can be installed either directly in the line to be
sampled (in-situ), or in a slip stream of a sample system (extractive). To assure a long and
accurate performance of the sensor, it should be protected from contaminants such as
liquids (water, oil etc.), and particulates. The sintered stainless steel sensor encapsulation
protects from particulates larger than 100 microns, finer particulates (e.g. from degraded
desiccant or rust) should be filtered with a particulate filter with suitable capability, do not
use hygroscopic filter materials.
4.1.1
In-situ installation
In-situ installation is recommended only for measurements where the gas pressure is
expected to be constant, the gas is expected to be free of contaminants, the gas
temperature is within the operating specifications of the sensor and there is no chance of
liquids coalescing. Examples of applications suited for in-situ installations are pure gases
or output of desiccant dryers (for instrument air), glove boxes, etc. For most other
applications in-situ installation should be avoided for the following reasons:
Sample conditioning is almost always necessary to avoid exposure of the sensor to
liquid water and other contaminants, such as hydrocarbons, which may damage the
sensor or affect accuracy over time.
If the gas line is under pressure, it is more likely that water condensation occurs which
may damage the sensor.
