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Care should be taken to ensure that the sample presented to the SADPminiEx is not
contaminated with any component that will damage, contaminate or affect the SADPminiEx
in a way that will impair the unit’s accuracy.
It is strongly recommended that the sample should not contain particulate matter, oil,
hydrocarbon or any other condensate. If these components contaminate the sample system
and/or the measuring sensor, the SADPminiEx response time will be lengthened, although
the sensor calibration will not be effected.
The flow rate, although not critical to the sensor measurement, should be low enough to
avoid abrasion to the sensor surface without being so low as to extend the SADPminiEx
response time to an unacceptable level. In general, a flow rate of between 5 and 8
litres/min at NTP will give the right balance.
The sensor used in the SADPminiEx is a variable capacitor, which is directly affected by
changes in partial pressure of water vapour, and these changes, that are proportional to the
dew/frost point temperature, are displayed on the instrument indicator.
pressure of water vapour, and these changes, that are proportional to the dew/frost point
temperature, are displayed on the instrument indicator.
4.1
Gases to Avoid
The moisture sensors are suitable for many different industrial and research applications.
Most gases can be checked for their moisture content with no need for the calibration to be
altered when changing between different gases, as the sensor operates only with reference
to the water vapour content. There are, however, some gases that must be avoided, as
they are not compatible with the material of construction of the sensor. Ammonia (NH
3
),
Ozone(O
3
) and chlorine (Cl) must be avoided at all times, even in small quantities.
Hydrogen chloride (HCl) also attacks the sensors very quickly. Some, less aggressive,
acidic gases, such as sulphur dioxide (SO
2
), can be monitored, as long as the moisture
content is low, generally less than 100ppm(v). If in doubt, please ask your supplier.
Sulphur hexaflouride (SF
6
) has no effect on the sensor. If the gas has been exposed to
arcing, however, it is possible that various acidic species will have been formed that will
corrode the sensor. When testing SF
6
that may have been arced, therefore, an acidity test
should be carried out first; if the gas proves to be acidic then the moisture test should not
be carried out.