DP2000 Portable Dew Point Analyzer Operations Manual
Super Systems Inc.
Page # 10 of 30
three degrees (3°) 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.
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 dry out 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 DP2000 measures both variables to compute the
displayed dew point.
HOW IT WORKS –
The dew point sensor is a “dielectric ceramic” that varies its electrical
capacitance with changes in relative humidity. The sensor is mounted in a short
probe, which is installed in a T-fitting that allows the sample gas to flow past the
sensor. The tip of this probe contains the dielectric ceramic relative humidity
(RH) sensor, as well as a built in temperature sensor to determine its dry bulb
temperature. Information from both of these sensors is used to compute the
resultant dew point, which is displayed on the digital LED display.
MAINTENANCE / SAFETY ISSUES –
One of the added features of the DP2000 is the ability to monitor the sensor’s
operating temperature through the built-in thermistor in the probe tip. The
temperature of the sample gas can be determined by pressing the switch labeled
“Sensor Temp”. It is spring loaded, so it will automatically return to displaying
dew point.
Maintaining proper sensor temperature will prevent the premature failure of the
sensor. The operating temperature of the sensor should remain below 140
F
(60
C) at all times. Periodic checks of the sensor temperature will verify that the