Vaisala Spectrum 4.0 - Manual (Page 76)

Glossary
70
A– B
C–E
F–K
L–Q
Ambient temperature The average or mean temperature of the surrounding air that comes in con-
tact with the equipment or instrument.
Axis A line that borders one side of the graph area, providing a frame of reference
for measurement or comparison. In Spectrum software, measurement values
are plotted on the vertical Y-axis while date and time values are plotted on the
horizontal X-axis.
Calibrate To compare and correlate readings against a standard measurement.
Calibration certificate Documented evidence that a product has been calibrated against a standard
measurement reference and that it falls within the specified requirements.
Channel The path through which an instrument receives the input signals it measures.
Dewpoint Dewpoint is defined as the temperature at which the amount of moisture
present in the air is the MAXIMUM amount the air can hold (at a constant
pressure and water vapor content). This means that when the temperature
falls to the dew point, the relative humidity is 100% and the air is considered
saturated.
Dewpoint does not vary with temperature, as does relative humidity (RH).
Rather, dewpoint is a DIRECT measure of the actual moisture content in the
air and thus is preferred as the unit of measurement in many scientific and
industrial applications—particularly in tightly controlled environments where
precise indications of water content in the air are required.
The dewpoint is never greater than the air temperature. Once the dewpoint is
reached and the air temperature continues to drop, water vapor is forced to
leave the air through condensation. This condensation may take the form of
water droplets, dew, or may remain suspended in the air as clouds or fog.
To better understand how dewpoint and relative humidity are related to each
other, try inserting a logger file with relative humidity (RH) channel values into
a graph twice—once, displaying RH using dewpoint and once displaying RH
using relative humidity.
In Spectrum, dewpoint readings below 0 degrees C are recorded as frost-
point.
Graph file A file that is created to display the data from one or more Logger files. Graph
files retain formatting information such as graph title, zoom levels, Y-axis scal-
ing, and Logger file data; and are identified by their .spg extension (for exam-
ple, LAB_1.spg).
Local time A value equal to the current time used at a particular location. A relative indi-
cator of time meaningful only if Time Zone Information is also known. Local
Time contrasts with UTC Time, an absolute time reference. The software
records Local Time and UTC Time in each Logger file.