Super Systems Simple Dew - Manual (Page 6)

Simple Dew Digital Dew Point Analyzer Operations Manual
Super Systems Inc. Page 6 of 18
tip can be cleaned by carefully removing it from the sample block (see Section 2.0 of the Field
Calibration instructions) and rinsing it in isopropyl alcohol. The power should be off while this is
done, and the power should remain off for at least 30 minutes after this procedure to allow all of
the alcohol to completely evaporate.
Water / Moisture Contamination
When a furnace or generator is being started up or cooled down, the resulting gases will
contain unusually high amounts of CO
2
. When these gases cool, moisture will precipitate out
and become condensation inside the sample tubing assembly. Even if the furnace or generator
is operating normally, residual moisture may still be present in the sample tube or plumbing
system. In the same way that the ports are checked for soot (see above) they should be checked
for moisture before attaching the instrument. This is especially important when taking a
sample from a generator, since the sample port is usually preceded by a significant amount of
plumbing. All traces of moisture should be eliminated before attaching the instrument. Failure
to do so will result in erroneous measurements and could result in damage to the analyzer.
The first signs of moisture in the instrument will be visible condensation collecting in the bowl
filter and an unusually high dew point. The upper range of the sensor is +80°F, so if that value
is displayed on the instrument it is probably due to the presence of moisture. If this moisture is
not removed, it will cause the sensor tip to corrode and will eventually require the sensor to be
replaced.
To remove moisture from the instrument, the filter should be removed from the instrument
(since it will probably be wet) and an inert gas such as Nitrogen or Argon should then be flowed
through the instrument for as much time as it takes to dry out. This dry-out time will depend on
the amount of moisture present in the instrument. The condition of the sensor can be
monitored by periodically reading the dew point from the display and watching the value
decrease over time. To test if it is operating properly, verify the ambient dew point against a
web-based weather station that will report the ambient dew point for your area. If the displayed
reading is within three degrees of the reported dew point when the instrument is taken outside,
then all of the moisture has probably been successfully removed. The wet filter and sample
tubing can be re-attached after they have been completely dried out. The filter element will
regain all of its original filtering properties after it has dried out.
To prevent the possibility of moisture damaging the instrument, be sure that the measured dew
point is below ambient levels before it is stored. If necessary, Nitrogen or Argon can be used to
purge the instrument after use.
What Is Dew Point?
Dew point can be defined as the temperature at which the water vapor pressure of the gas
equals the saturated water vapor pressure. In other words, it is the temperature at which
condensation will just begin to occur as the gas is cooled. Dew point and relative humidity are
not the same measurement. Relative humidity is the amount of water vapor in the air compared
to the amount the air could hold if it was totally saturated, and it is expressed as a percentage,
not a temperature. To determine dew point, two main variables are required: Relative Humidity
and Temperature. The Simple Dew measures both variables to compute the dew point.
How It Works