Kestrel 4000 - Manual (Page 6)

Kestrel ® 4000 Pocket Weather ® Tracker 11
• Ideally, provide an airflow of at least 1 M/S (2.2 MPH), over the temperature sensor—point the
Kestrel Meter into the airflow. If there is no airflow, simply wave the unit back and forth so air
passes over the sensors. With airflow over the temperature sensors and humidity chambers,
readings within specifications will be provided within two to three minutes, even after a large
temperature shift.
• If no airflow can be provided, you must allow sufficient time for the RH value to stabilize. This can
take as long as 20 minutes—the greater the temperature change, the greater the time. You can
use the logging capability of the Kestrel Meter to confirm that the unit has stabilized to
a correct reading: Set the memory options to a relatively short logging interval (20 seconds
works well), select the graphical display of RH, and you can see when the value is no longer
changing significantly. At that point, the RH value is stable and can be relied upon to be within the
accuracy specifications.
Barometric Pressure and Altitude Adjustment
The Kestrel Meter measures “station” pressure—the actual air pressure in the measurement location—and
uses this value to calculate barometric pressure and altitude. Station pressure changes in response to
two things—changes in altitude and changes in the atmosphere. Because the Kestrel Meter is constantly
changing location and altitude, it is important to enter adjustments or “references” when accurate pressure
and altitude readings are needed.
Barometric pressure is station pressure corrected to sea level. In order to make the correction, the Kestrel
Meter needs an accurate reference altitude. Altitude is the height above sea level. In order to correctly
calculate altitude, the unit needs an accurate barometric pressure reference, also known as an “altimeter
setting”. Fortunately, you only need to know ONE of these values (current barometric pressure or current
altitude) in order to set your Kestrel Meter up to show accurate readings.
Starting with the known barometric pressure for your location: You can obtain your
current barometric pressure by checking an internet weather site for a nearby location,
or contacting a local airport. Set this value as your reference pressure on the ALTITUDE
screen to determine your correct altitude: Press the button to enter the reference
setting mode. Press the button to increase the reference pressure or the button to
decrease the reference pressure. You will notice that the altitude will change with changes in the reference
pressure. Press the button to exit the adjustment mode. Set your Kestrel Meter down on a table and
allow the altitude reading to stabilize. (Note: very small changes in pressure generate noticeable changes
in altitude. In order to provide meaningful readings for activities where altitude changes quickly, the Kestrel
Meter features rapid altitude response. This is why the altitude readings tend to fluctuate by a few feet.)
After obtaining a current altitude from the ALTITUDE screen, move to the BARO screen and enter this value
as your reference altitude by following the same procedure. Both readings will now be accurate.
Starting with a known altitude for your location: You can obtain your altitude from a
topographical map or local landmark. Google Earth is an excellent free program that
provides the exact altitude for any given address: www.earth.google.com/. Set this
value as your reference altitude on the BARO screen to determine your barometric
pressure. Press the button to enter the reference setting mode. Press the button
to increase the reference altitude or the button to decrease the reference altitude. You will notice that
the barometric pressure will change with changes in the reference altitude. Press the button to exit the
adjustment mode. Again, allow the Kestrel Meter to stabilize, then enter the value from the BARO screen
as your reference pressure on the ALTITUDE screen by following the same procedure. Both readings are
now accurate.
When reviewing stored data, remember that changes in pressure AND changes in location/altitude will
affect the stored values. When tracking pressure changes relative to weather, set the reference altitude on
the BARO screen and keep the Kestrel Meter in one location. Your graph history will now show trends in