16
Magellan MX Weather Station
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Columbia Weather Systems, Inc.
Principles of Measurements
Temperature & Relative Humidity (MX300, MX500, MX501
and MX600)
Temperature & Relative Humidity are measured by an internal solid-state
instrument contained inside a solar radiation shield with a double louvre
design.
Wind Speed & Direction (MX200, MX500, MX501 and
MX600)
The wind sensor measures the times taken for an ultrasonic pulse of
sound to travel from the North (N) transducer to the South (S) transducer
and compares it with the time for a pulse to travel from S to N
transducer. Similarly, times are compared between West (W) and East
(E), and E and W transducer. For example, if a North wind is blowing,
then the time taken for the pulse to travel from N to S will be faster than
from S to N, whereas the W to E, and E to W times will be the same. The
wind speed and direction can then be calculated from the differences in
the times of flight on each axis. This calculation is independent of any
factors such as temperature.
Barometric Pressure (MX300, MX500, MX501 and MX600)
Barometric Pressure is measured by a solid-state device fitted on to a
circuit board inside the sensor housing.
Rainfall (MX600)
Rainfall is measured by using an optical infra-red beam sensor. Infra-
Red beams bounce off the inner optical surface between transmitters
and receivers. As rain drops
make contact with the sensor surface, some
of the
infra-red beams are
allowed to escape. The sensor detects the
change in beam intensity and determines the size of the rain drop that
caused the change. Through digital signal processing the output
simulates a tipping bucket rain gauge measurement.
Solar Radiation (MX501)
Solar Irradiance is measured using a high quality Hukseflux LPO2
second class Solar Radiation Sensor/Pyranometer which complies with
ISO 9060. This highly accurate instrument uses thermopile technology to
measure hemispherical solar radiation from a 180-degree field of view
angle.
