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(2) Humidity is a difficult parameter to measure electronically and drifts over time due to
contamination. In addition, location has an adverse affect on humidity readings
(installation
over
dirt
vs.
lawn
for
example).
Official stations recalibrate or replace humidity sensors on a yearly basis. Due to
manufacturing tolerances, the humidity is accurate to ± 5%. To improve this accuracy,
the indoor and outdoor humidity can be calibrated using an accurate source, such as a
sling
psychrometer.
(3) The display console displays two different pressures: absolute (measured) and relative
(corrected to sea-level).
To compare pressure conditions from one location to another, meteorologists correct
pressure to sea-level conditions. Because the air pressure decreases as you rise in
altitude, the sea-level corrected pressure (the pressure your location would be at if
located at sea-level) is generally higher than your measured pressure.
Thus, your absolute pressure may read 28.62 inHg (969 mb) at an altitude of 1000 feet
(305 m), but the relative pressure is 30.00 inHg (1016 mb).
The standard sea-level pressure is 29.92 in Hg (1013 mb). This is the average sea-
level pressure around the world. Relative pressure measurements greater than 29.92
inHg (1013 mb) are considered high pressure and relative pressure measurements
less than 29.92 inHg are considered low pressure.
To determine the relative pressure for your location, locate an official reporting station
near you (the internet is the best source for real time barometer conditions, such as
Weather.com or Wunderground.com), and set your weather station to match the official
reporting station.
(4) Only use this if you improperly installed the weather station sensor array, and did not
point
the
direction
reference
to
true
north.
(5) The default conversion factor based on the wavelength for bright sunlight is 126.7 lux /
w/m
2
. This variable can be adjusted by photovoltaic experts based on the light
wavelength of interest, but for most weather station owners, is accurate for typical
applications, such as calculating evapotransporation and solar panel efficiency.
(6) Wind speed is the most sensitive to installation constraints. The rule of thumb for
properly installing a wind speed sensor is 4 x the distance of the tallest obstruction. For
example, if your house is 20’ tall and you mount the sensor on a 5’ pole:
Distance = 4 x (20 – 5)’ = 60’ or =4 x (6.10-1.52)=18.32m.
