Kestrel® RH Calibration Kit
Each
Kestrel Pocket weather Meter is individually calibrated after
assembly. In essence, each unit is "taught" what the correct relative humidity
(RH) values should be for given signals from the RH sensor.
NK calibrates at RH=32.8% and RH=75.3%. Calibration
is done in two sealed environmental chambers maintained
at 25°C. The humidity
is held constant with saturated aqueous salt baths: magnesium chloride
for the RH 32.8% chamber and sodium chloride for the 75.3% chamber.
Chamber temperatures are held constant at 25°C ± 0.5°C
The temperature and RH of each chamber is independently
monitored using a precision chilled mirror dew point
hygrometer (EdgeTech Model 2002) accurate to ± 0.1Cº and NIST (National
Institute of Standards and Technology) traceable. A proprietary
auto calibration routine controls the calibration process. After
60 minutes this routine stores a calibration value which forces
the Kestrel to be correct at the RH value of the chamber.
The
response of the humidity sensor is a highly reproducible, non-linear
curve. This non-linear characteristic is stored in the microprocessor
used to compute RH, and in this manner we are able to maintain
an accuracy of ± 3% of scale over the relative range 5%
- 95%.
Field
Calibration
The Kestrel should be recalibrated if the RH sensor has been
replaced or has shown drift in its RH measurement. Field calibration requires the use of the RH Calibration Kit. For instructions related to the field calibration procedure, please view the Field Calibration Kit Manual. This manual explains in detail all of the steps for recalibrating your Kestrel. This process will take approximately 13 hours, including setup and calibration.
Contents
of the RH Calibration Kit The RH calibration kit includes the following items:
- three
clear, sealable containers
- one
container with magnesium chloride solution
 one
container with sodium chloride solution
- two
wooden scrapers
- an
insulated carrying case to hold all of the above and maintain
a stable environment while performing calibration
The
large container is used to create a stable environment.
The small containers are used to hold the saturated salt
solution. The saturated salt solutions generate well-defined
humidities when they are confined to a contained environment.
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