Exergen D-Series - Manual (Page 4)

51 Water Street, Watertown, MA 02172 USA
800-422-3006 • 617-923-9900 • Fax 617-923-9911
Infrared
Psychrometry
with the
Microscanner
D-Series:
Measure
Relative Humidity
to
Certified Accuracy
±
0.5% RH
Psychrometrics, the science of measurement and
control of moisture in air, is based entirely on
thermodynamics of air and water: the properties and
temperature . Relative humidity (RH) is one of the
common parameters used to describe the psychro-
metric state of air in an environment, in an oven, or
any area where moisture content can influence
product quality or personnel comfort.
The accurate and reliable measurement of RH is
one of the most challenging tasks in industry, and
has included devices such as chilled mirrors, lithium
chloride cells, aluminum oxide sensors, capacitance
polymer sensors, hair hygrometers, carbon
hygristors, and a wide variety of technologies to
meet the requirements. Calibration and certification
has been even more difficult, due to the fact that
most humidity measuring devices employ
indirect
methods and therefore have limited traceability.
The Infrared Psychrometry method with the D-
Series is a direct application of the thermodynamics
and mathematics that defines humidity: the D-Series
is capable of measuring the true wet-bulb tempera-
ture accurately, and with the dry-bulb temperature,
the RH can be computed to a very high accuracy via
standard psychrometric equations. The process is
as follows:
A porous material (filter paper is suitable) is wetted
with water (purity is not important), and air from the
environment flows across the surface to bring the
surface to thermodynamic equilibrium with the air,
i.e. to the lowest possible temperature produced by
the evaporating water, which is the wet-bulb tem-
perature.
Air Flow
Wet Porous Material
Thin layer of evaporating water
at thermodynamic equilibrium:
wet-bulb temperature
A MUST FOR
ISO 9001
ISO 9002
ISO 9003
TRACEABILITY
PROGRAMS
™
D-Series Handheld IR Scanners