3 Installaon
3.1 Gases to Avoid
The SHAW moisture sensors are suitable for many dierent industrial and research
applicaons. Most gases can be checked for their moisture content with no need
for the calibraon to be altered when changing between dierent 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 compable
with the material of construcon of the sensor. Ammonia (NH
3
), Ozone (O
3
) and
Chlorine (Cl
2
) must be avoided at all mes, even in small quanes. Hydrogen
Chloride (HCl) also aacks 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 Hexauoride (SF
6
) has no eect 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 tesng SF
6
that may have been arced, therefore,
an acidity test should be carried out rst; if the gas proves to be acidic then the
moisture test should not be carried out.
3.2 Installing the Air/Gas Sampling System
The Piping Installaon Schemac diagram (see secon 3.3) shows all components,
which could be used in a dry gas measurement applicaon. Although not all the
items shown will be required for every installaon.
The main principle when considering the presentaon of the gas sample to the
SDHmini dewpoint meter is to keep the sample system as simple as possible and
of minimum swept volume, so that it has the least possible inuence on the gas
sample.
The maximum pressure to which the telescopic
measuring head is exposed should not be more than
0.3 bar, 4 psi
Exposing the measuring head to higher pressures may
damage the instrument and result in injury to the
operator or other personnel in the area.
7
2.3 Pressure Exposure
!
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