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Emerson Process Management GmbH & Co. OHG 3-15
X-STREAM X2
Instruction Manual
HASX2E-IM-HS
02/2012
3
Measuring Principles
3.4 Trace Moisture Measurement
Fig. 3-14: Trace Moisture Sensor Assembly
1 Sensor
2 Sensor block
3 Gas connections
3.4 Trace Moisture Measurement
1
2
3
The Trace Moist
ure sensor is a robust
2-wire-transmitter, using dew point impe-
dance measurement for continuous moisture
measure
ments in gases and gas mixtures.
It makes dew point measurement as ac-
cessible as temperature and pressure.
Some denitions:
The dew point
is the temperature in Deg C
to which a given parcel of humid air must be
cooled, at constant barometric pressure, for
water vapor to condense into water. The con-
densed water is called dew. The dew point is
the saturation temperature.
The dew point is associated with relative
humidity. A high relative humidity indicates
that the dew point is closer to the current air
temperature. Relative humidity of 100 % in-
dicates the dew point is equal to the current
temperature and the air is maximally satu-
rated with water. If the dew point remains
constant and temperature increases, relative
humidity will decrease.
Humidity is the amount of water vapor in the
air. Relative humidity is dened as the ratio
of the partial pressure of water vapor (in a
gaseous mixture of air and water vapor) to
the saturated vapor pressure of water at a
given temperature.
This type of sensor is used, if dew point
measurements are required.