RST meteoscan 937PRO, Operation Manual, Page: 27 / 68

RST01937 meteostanciya
page 27
Place the sensor in a shaded, controlled environment next to the fluid thermometer, and allow the
sensor to stabilize for 48 hours. Compare this temperature to the fluid thermometer and adjust the console
to match the fluid thermometer.
(2) Humidity is a difficult parameter to measure electronically and drifts over time due to contam-
ination. 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 tol-
erances, 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/m2 .
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’.
Many installations are not perfect and installing the weather station on a roof can be difficult. Thus,
you can calibrate for this error with a wind speed multiplier.
In addition to the installation challenges, wind cup bearings (moving parts) wear over time.
Without a calibrated source, wind speed can be difficult to measure. We recommend
using a calibrated wind meter (available from Ambient Weather) and a constant speed,
high speed fan.
(7) The rain collector is calibrated at the factory based on the funnel diameter. The bucket tips
every 0.01” of rain (referred to as resolution). The accumulated rainfall can be compared to a sight glass
rain gauge with an aperture of at least 4”.
Make sure you periodically clean the rain gauge funnel.
Note : The purpose of calibration is to fine tune or correct for any sensor error associated with the de-
vices margin of error. Errors can occur due to electronic variation (example, the temperature sensor is a
resistive thermal device or RTD, the humidity sensor is a capacitance
device), mechanical variation,
or degradation (wearing of moving parts, contamination of sensors).
RST01937Manual 25.10.2017 11:57 Страница 27