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Optidew User's Manual
3.
Particulates – particulates passing over the sensor can build up on the
mirror over time. This can cause a loss of mirror reflectivity. DCC will
compensate for this by taking into account anything on the surface of
the mirror when resetting the optical condition, however if the problem
becomes too severe, the 'mirror contamination warning' symbol will be
displayed in the Sensor Status display.
4. Sample temperature – consider the difference between the sample
temperature and the dewpoint temperature. Make sure that the sensor
you are using has the cooling capability to make the measurement (see
section 4.5. for further information). If the sensor does not have the
necessary cooling capability, then you should consider an extractive
system so the sample can be cooled prior to measurement.
5. Sample pressure – If you are interested in readings in terms of ppm
or g/m
3
pressure. You can then either enter this pressure into the Optidew via the
'Inputs' screen (see section 3.2), or connect a pressure sensor directly to
the point of measurement (see section 2.6).
Extractive
If the sensor will be mounted into a sample conditioning system, then the above points
are still of relevance, but the following should also be considered:
1.
Extraction point – make sure that the chosen extraction point is
representative of the process, i.e. that the sample of interest is flowing
past the extraction point, and it is not being pulled from a dead volume.
2.
Enclosure and sample line heating – if the sample has a dewpoint
greater than ambient temperature, then all components upstream of the
sensor will need to be heated to at least 18°F/10°C above the sample
dewpoint to ensure the water remains in vapor phase.
3.
Sample block flow path – the sensor block must be configured with
gas inlet and outlets installed in the side ports. The top is either blanked
or used to install a pressure transmitter. If replacing an old Optidew
installation then be aware that using the old sensor block will
result in poor response speed at low dew-points, as it does not
allow enough flow across the mirror.
Kahn Instruments
Mirror contamination warning symbol
Figure 26
Insure that the sensor is positioned in an environment of known
OPERATION
V
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