Kestrel 3500 - Manual (Page 6)

Kestrel® 3500 Pocket Weather® Meter 11
High Speed Use
After numerous hours of sustained operation over 25 M/S (~49 KT, 90 KM/H, 56 MPH or 4,923
FPM), the Kestrel will lose some accuracy due to wear of the pivot
and bearings in the impeller.
Replacing the Impeller
You may recalibrate the wind speed readings by replacing the
impeller. Press FIRMLY on the sides of the black impeller housing
with your thumbs to remove the entire assembly. When inserting
the new impeller, be sure the arrow is facing the display side of
the unit, and is aligned with the top of the meter. Press on the
sides of the housing rather than the center.
Taking Accurate Humidity, Heat Stress and Dewpoint
Measurements
The patented system for measuring relative humidity allows for extremely fast and accurate
readings. The sensor is located in the large hole on the rear of the unit. Even extreme and
abrupt changes in the surrounding humidity will be measured within several minutes. To
test this, place your hand around the rear of the unit. Within several seconds, the humidity
will increase dramatically. After removing your hand, the humidity will quickly begin to
decrease. Next, place your hand near the rear of the unit and wave the unit back and forth.
The humidity will not change because the air flow is diluting the humidity from your hand.
This example shows the importance of keeping air flow past the sensor while taking a
measurement. If there is no natural air flow past the sensor, wave the unit back and forth.
It is also reasonable to lay the unit down on a solid surface for several minutes to allow the
sensor to adjust.
Sensor Calibration
All the sensors have been factory calibrated to be accurate within specifications. For
recalibration, you may either return it to Nielsen-Kellerman for factory calibration, or contact
NK for field calibration instructions. Humidity Field Calibration Kits are also available for
sale online.
About the Backlight
The Kestrel 3500 has an aviation green electroluminescent backlight. The Kestrel 3500 NV
has a night-vision preserving backlight which helps users to sustain natural night vision.
The NV’s backlight incorporates an optical filter to reduce overall brightness and minimize
blue and green spectrum light to preserve night vision. Additionally, the backlight is much
dimmer than a standard backlight, making it more difficult to detect with the naked eye in
night operations. This backlight appears soft greyish pink (not red) and is still in the visible
spectrum, so it is not compatible with night-vision equipment.
It takes 30 to 45 minutes for the average eye to adapt to darkness and maximize night
vision. Even a short burst of white, yellow, green or blue light “bleaches out” the rod cell
photoreceptors in the eye and causes night blindness until the entire adaptation process can
take place again. Light in the red spectrum does not cause this “bleaching out”, preventing
night blindness and night vision fatigue.
Replacing the Impeller