Servomex AquaXact 1688, Руководство оператора

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AquaXact Issue 1.0 © Servomex Group Limited 2017
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9 Storage and disposal
Storage 9.1
All Servomex AquaXact 1688 Al
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sensors and replacement tips are shipped in glass
storage bottles in order to maintain sensor integrity. The storage bottle is partially filled
with a desiccant to keep the sensor dry and ready for use.
Figure 9-1: AquaXact 1688 Al
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sensor glass storage bottle
The storage bottle can be used for long term storage provided the correct procedures are
followed.
The AquaXact ultra-thin film sensor technology is based on the ability of the sensor to
react to changes in the partial water-vapor pressure in the surrounding gas stream. In a
constant moisture level environment, the rate of absorption and desorption of water
molecules reaches equilibrium with the surrounding gas stream based on the partial water
vapor pressure in the gas environment. Once equilibrium is achieved, the change in the
dielectric strength of the aluminum oxide layer based on the amount of water present in
the layer is accurately sensed as a change in capacitance of the sensor. The ability to
absorb and desorb water molecules in the aluminum oxide layer is based on a certain level
of water molecules being present in different chemical structures within the aluminum
oxide which act as receptor sites.
Because the desiccant in the storage bottle continues to absorb moisture as long as the
sensor remains sealed in the bottle the sensor can dry down to extremely low levels.
Holding the sensor at extremely low moisture levels for long periods of time (more than 3
months) can cause the sensor response to be sluggish when first put into service.
The slow response phenomenon after a long storage period is driven by the fact that the
desiccant continues to absorb water molecules. As a result after a long storage period in
this environment the majority of the water molecules in the chemical structures of the
aluminum oxide layer have been removed, reducing the ability of the senor to absorb
water. When the sensor is then exposed to a gas stream with a partial water vapor
pressure within its normal detection range, the sensor first has to ‘rehydrate’ before it can
start to respond normally.