Kestrel® 3500DT Pocket Weather® Meter
7
response time (see temperature section above). Readings should be taken in the shade.
Heat Stress
– combination of temperature and humidity, as defined by the US National
Weather Service. Heat stress is the effective temperature on a human or animal at high
temperatures due to humidity. Heat stress readings will be the same as the temperature
readings below 70ºF.
Dewpoint
– calculated based on temperature and humidity measurements, as a measure of
moisture content in the air. If the dewpoint is very close to the temperature, the air is humid.
If the temperature and dewpoint are the same, dew will form. If this happens below freezing,
frost will form.
Wet Bulb Temperature
- calculated based on temperature and humidity measurements, as a
measure of evaporation rate. If the wet bulb temperature is very close to the air temperature,
the air is humid. Wet bulb temperature is typically measured by swinging a mercury
thermometer with a wet sock on its end for several minutes.
Delta T
- calculation of the dry bulb temperature minus the wet bulb temperature as a
measure of evaporation rate. Primarily used in spraying applications, this measure provides
an indication of droplet survival. For example, it is not recommended to apply pesticides
when Delta T is above 10. A range of 2 to 8 (degrees C) is ideal. The Kestrel 3500 Delta T uses
a pressure-corrected wet bulb temperature, ensuring accuracy in all conditions.
Altitude and Barometric Pressure
- the Kestrel 2500 will measure station pressure in order
to calculate barometric pressure and altitude. Changes in either air pressure or altitude will
affect these readings, so it’s important to make adjustments as necessary.
First, you will need to obtain either (a) the current barometric pressure or (b) the altitude of
your location. You can obtain your current barometric pressure by contacting a local airport
or weather service. Set this value as your reference pressure on the ALTITUDE screen to
determine your altitude. Otherwise, you can obtain your altitude from a topographic map
or local landmark. Set this value as your reference altitude on the BAROMETRIC PRESSURE
screen to determine your barometric pressure.
There are two examples for when and how to use the BAROMETRIC PRESSURE and
ALTITUDE screens.
First, assume that you know the altitude from one of the sources above. Set the reference
altitude on the BAROMETRIC PRESSURE screen to this elevation. As long as you remain
at home, you can accurately track changes in the barometric pressure. However, the
measurement on the ALTITUDE screen also changes. This value will fluctuate as pressure
fronts pass through your location. Since you know your house in not changing elevation, you
can ignore this screen.
Now let’s assume that you are planning a day hike and you’d like to track your altitude.
Before starting, you’ll need to adjust the reference pressure on the ALTITUDE screen. You
can do this by simply adjusting the reference pressure until you reach the elevation of your
house. The reference pressure will be the same as the pressure reading on the BAROMETRIC
PRESSURE screen. You can now track the altitude as you hike. You can ignore the values on
the BAROMETRIC PRESSURE screen, since the pressure changes are predominantly due to
changes in elevation.
As with all pressure altimeters, it must be assumed that any change in pressure due to
weather is small over the course of one day. If you were to encounter an elevation landmark,
you can adjust the reference pressure until the altitude matches the landmark elevation. This
Shop for Kestrel products online at:
1.877.766.5412
www.
WeatherMeters-Direct
.com
