Kestrel 5, 3000 Series, 4 Series, 3500 Series Series Manual

Relative Humidity Calibration Kit

For calibrating the following Kestrel Meters

Kestrel 5 Series, 4 Series and Kestrel 3000-3500 Series

(Kestrel DROPs currently cannot be recalibrated)

Kestrelinstruments.com 800.784.4221

●●●●●

While the calibration process is simple, it is important that you follow the
steps carefully. A careless calibration could enter incorrect values into the
unit and degrade its performance.

●●●●●

©2019 Nielsen Kellerman Co. Kestrel, the Kestrel bird, NK, Nielsen-Kellerman and the
NK logo are registered trademarks of the Nielsen-Kellerman company.

Please refer to Standard Practice for maintaining Constant Relative Humidity by Means
of Aqueous Solutions ASTM Designation E104-85 (reapproved 1996) for additional
information.

2

Factory Recalibration / Certication

The Kestrel should be recalibrated if the RH sensor has shown drift in its RH measurement. The Kestrel RH
sensor is specied to develop less than 2% drift over 24 months. You may return your Kestrel to NK for Factory
Recalibration of the relative humidity and related measurements. Recalibration is available with and without
certication of NIST traceability and calibration stickers. Note that NK can recalibrate and certify any of the
values measured by your Kestrel. Please contact NK for more information about Factory Recalibration and
certication.

RH Factory calibration of Kestrel 5 Series units will return units to within +/-2% accuracy spec.
RH Factory calibration of Kestrel 3000-3500 & 4 Series units will return units to within +/-3% accuracy spec.

Field Recalibration

As an alternative to Factory Recalibration, this kit allows you to perform dozens of humidity recalibrations in
the eld to improve sensor accuracy and address the eects of RH drift. This manual explains in detail all of the
steps for recalibrating your Kestrel’s humidity Sensor. This process will take approximately 50 hours, including
setup and calibration. Ensure that you are performing the calibration in a climate controlled environment such
as a home or oce and make sure your calibration location is not near any windows or air conditioning or heat­ing vents. Even temperature uctuations as slight as 2 deg F while calibrating can negatively impact accuracy,
so if you are not sure that your calibration environment is stable, place the entire Cal Kit inside an insulated
cooler or if a cooler is not available, wrap it in a thick blanket. Further temperature control can be gained by
placing additional containers of room temperature water inside the cooler or blanket, (gallon jugs work ne).

RH Field calibration of Kestrel 5 Series, 4 Series and 3000-3500 Series units will typically return units to
within +/-3% accuracy but actual results can vary depending on the user’s ability to control the calibration
environment.

Please read the complete instructions for your unit before

beginning the recalibration of your Kestrel

3

Contents of the Humidity Calibration Kit

» Two jars with color-coded salt chamber labels, plastic spacer grids and sealing lids
» One jar with no spacer grid (for water)
» One vial with magnesium chloride (MgCl) salt and blue color-coded label
» One vial with sodium chloride salt (NaCl)and red color-coded label
» One RH Calibration Kit insulated bag/carry case
» One color-coded labeled measuring cup

Note: Our calibration process has changed. The changes will require more time but will improve relative
humidity calibration accuracy vs. the previous method. Please familiarize yourself with the new process.

Note: Only place one Kestrel unit in each calibration jar at a time. Attempting to calibrate more than one
unit in each jar at the same time will reduce RH calibration accuracy. If you are attempting to calibrate
multiple units the process can be overlapped so that while the rst Kestrel unit is equilibrating in the
second jar, the second Kestrel unit can begin equilibrating in the rst jar.

Note: We have found that when using this Kestrel Relative Humidity Calibration Kit, setting the second
calibration point to 74.0% RH rather than 75.3% as previously recommended produces a more accurate
calibration. This value is specic to calibrating with this kit. If a dierent method is used for generating a

reference RH for calibration, the expected RH value for that method should be used.

4

Preparing the Calibration Salt Solutions

» For your rst use only, you will need to add water to the provided salts to prepare the saturated salt

solutions for the calibration chambers.

» Note that it is important not to cross-contaminate either salt solution with the other salt. For this reason,

every item is color-coded. Make sure to keep red items with red, and blue with blue, throughout the

mixing and calibrating process.

» You will be mixing the salts with water. We recommend distilled water if available, but clean

uncontaminated tap water will not measurably aect the accuracy of your results.

» For both solutions, your aim is to produce a “slurry” in which you can still see visible grains of salt as well

as a small amount of liquid water above the salt.

1. Open the two labeled jars. Remove the two plastic spacer grids from the jars.

2. Open the sealed vial labeled “Sodium Chloride 74.0% (High)” and empty the salt into the bottom of the
jar with the same label.

3. Fill the small measuring cup to the RED line marked “NaCl” (13 ml.) with distilled or clean tap water.
Add to jar.

4. Using a stirring stick, stir the solution for at least a minute. Please do not shake jar to stir as this will
deposit salts on the side of the jar, aecting the overall solution. Observe the consistency. If necessary,
add a few drops of water to achieve the desired slurry consistency, and stir some more.

5. Place the lid with the same label on the jar and tighten securely.

6. Repeat for the Magnesium Chloride 32.80% (Low) solution, lling the measuring cup to the BLUE line
marked MgCl (5 ml.) and using the BLUE color-coded supplies. You may need to use a stirring stick to
scrape the salt out of the vial or bag.

5

7. Make sure not to pour in more than 5 ml. of water! It is better to start with slightly less water, and add it
a drop at a time, as this solution tends to absorb water quickly and become too wet.

8. Return the two plastic spacer grids to their jars so the feet sit down in the salt slurry.

9. Fill the empty third jar with room temperature water.

10. For Kestrel 4 and 5 Series units, remove the lanyard.

11. For Kestrel 3000-3500 Series units, remove the lanyard keeper and slide the protective case o the
lanyard. Fold the lanyard a couple times to shorten it and ax with a small rubber band so that the full
lanyard length is shorter than the Kestrel 3000-3500 body and that the lanyard cannot come in contact
with the salt solution when the unit is placed upside down in the jar.

12. Only calibrate one Kestrel unit in the jar at a time. Attempting to calibrate more than one unit at a time
will reduce RH calibration accuracy.

Note: The plastic spacers should not be used for the calibration of the Kestrel 4400/4600 and 5400 as they
will not t. When placing the Kestrel 4400/4600 or 5400 in the jar, inserting it upside down is recommended.
The black globe is more easily cleaned when transferred from one salt jar to the next than the bottom of the
Kestrel.

Note: The salt solutions will tend to change over time. The NaCL solution will tend to dry out, and the MgCl
solution will tend to pull humidity from the air and get too wet. For this reason, keep the lids securely closed
on the calibration chambers except when opening them to load a unit for calibration. You may add drops
of water to the NaCl solution to return it to the proper “slurry” consistency if required. You may also place
the MgCl solution in a clean pan in a slow oven to dry it if it becomes too wet, or you may simply purchase
replacement salt jar and remix the solutions from scratch.

6