3 Installation
3.1 Gases to Avoid
The SHAW 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
2
) 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 Hexafluoride (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.
3.2 Installing the Air/Gas Sampling System
The
Piping Installation Schematic
diagram (see section 3.3) shows all components,
which could be used in a dry gas measurement application. Although not all the
items shown will be required for every installation.
The main principle when considering the presentation 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 influence 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
!
