Kestrel 4500 - RH Readings After Temperature Swings; BAROMETRIC PRESSURE AND ALTITUDE; Setting Reference Pressure and Altitude

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• If your circumstances force you to expose the Kestrel Meter to a large temperature swing prior to
taking a relative humidity reading (such as when taking a Kestrel Meter stored inside at 70° F outside
to a temperature of 40° F), you will need to take additional steps to ensure that the Kestrel Meter’s
external temperature sensor is in thermal equilibrium.
- Ideally, provide an airow of at least 1 M/S (2.2 MPH), over the temperature sensor - point the
Kestrel Meter into the airow. If there is no airow, simply wave the unit back and forth so air
passes over the sensors. With airow over the temperature sensors and humidity chambers,
readings within specications will be provided within two to three minutes, even after a large
temperature shift.
- If no airow can be provided, you must allow sucient 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 conrm 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 signicantly. At that point, the RH value is stable and can be relied upon to be within
the accuracy specications.
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.