===== Vaisala HMK15 Humidity Calibrator =====

  * Description: Calibration set up for Vaisala Humidity Sensors
  * Manufacturer: [[https://www.vaisala.com/en|Vaisala]]
  * Manufacturer Spec Site: [[https://www.vaisala.com/en/products/instruments-sensors-and-other-measurement-devices/instruments-industrial-measurements/hmk15|Vaisala HMK15 Humidity Calibrator]]
  * Model: HMK15
  * Manual: [[file:///C:/Users/vosas/Downloads/HMK15-User-Guide-M210185EN-E.pdf|HMK15 User Guide]]

==== Parts ====
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  * Main Board
    * Salt Solution Chambers (x2)
    * Sensor Cap Attachment (x2)
    * Sensor Cap Plugs (x10)
    * Thermometer
  * Measuring Cup
    * {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_140049.png?200|}}
  * Plastic Probe/Stirring Stick
    * {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_140059.png?200|}}
  * Adapter Rings (x3)
    * {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_143016.png?300|}}{{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_143025.png?300|}}
  * Salts
    * {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_135932.png?300|}}{{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_143008.png?300|}}
    * NaCl (75% RH)
    * K2SO4 (97% RH)
    * All available salts
      * Lithium chloride LiCl (11% RH)
      * Magnesium chloride MgCl2 (33% RH)
      * Sodium chloride NaCl (75% RH)
      * Potassium chloride KCl (85% RH)
      * Potassium sulphate K2SO4 (97% RH)
  * Calibration/Preparation Date Tags
    * {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_140023.png?300|}}
  * Certificate of Calibration/Inspection
    * {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-06-30_140036.png?300|}}


==== Calibration Process ====

Need:
  * HMK15 Humidity Calibrator
  * Vaisala Humidity Sensor
  * Deionized water

Steps:
  - Prepare salt solutions
    - Take the calibrator out of the box and place it on a clean, even surface.
    - Remove the transit cover of the salt chamber.
    - Remove the chamber lid from the chamber holder and put it aside.
    - Press the transit cover on the chamber holder.
    - Pour the required amount of ion exchanged water into the salt chamber.
      - LiCl: 12 ml
      - MgCl2: 3 ml
      - NaCl: 10 ml
      - KCl: 10 ml
      - K2SO4: 10 ml
    - Sprinkle the contents of a salt package (or measure the required amount of salt 1) in small quantities into the chamber, stirring constantly.
      - LiCl: 15 g / 18 ml
      - MgCl2: 30 g / 30 ml
      - NaCl: 20 g / 15 ml
      - KCl: 30 g / 30 ml
      - K2SO4: 30 g / 20 ml
    - When measuring with the measurement cup, make sure that the cup is clean and dry. Rinse and dry the cup after every use.
    - When all the salt has been sprinkled into the chamber, the saturated salt solution should have a ratio of 60… 90% undissolved salt to 10…40% liquid.
    - Close the salt chamber with the chamber lid.
    - Fasten the salt chamber on the holder in the base plate and close the measurement holes with rubber plugs.
    - The chambers can also be used individually, without the base plate.
    - The rubber plugs have three steps, each of which is suitable for a certain hole diameter: the first step for the 12 mm (0.47 in), the second step for the 13.5 mm (0.53 in), and the third step for the 18.5 mm (0.73 in) hole.
    - Keep the holes always closed when not calibrating.
    - Write the preparation date on a sticker and use it to mark the chamber. If you use a ready-dosed salt package, use the sticker with the batch code. Mark all parts of the salt chamber (chamber, chamber lid, and transit cover) with stickers. This way, the lids/covers and different salts do not get mixed.
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    - Allow approximately 24 hours for stabilization before use so that the salt solution reaches the equilibrium humidity.
    - Depending on the frequency of use and the general operating conditions, the salt solutions maintain their characteristics for 6 - 12 months, after which they must be replaced. Perform a visual check every 2 - 3 months. There must be a minimum of 10 % of undissolved salt at the bottom of the chamber (max. 90 %). The salt must be clean, otherwise it must be reprepared.
  - Calibrate Instrument
    - Remove the cover from the end of the thermometer and flip it around the other way.
    {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-08-14_135625.png?400|}}       {{:atmos:citation:instruments:vaisalahmk15calibrator:screenshot_2026-08-14_135604.png?400|}}
    - Complete the following steps twice, once for each solution. Ensure that the probe head does not get wet.
      - Insert the thermometer into the largest hole of the calibration cover of the solution.
      - Remove the cover on the probe and insert into the calibration cover.
      - Wait for the reading to stabilize, and record both the humidity reading and the temperature
        - This could take 10-30 minutes.
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      - Repeat for the second solution.
  - Adjust instruments
    - Using the values you recorded and the following table, find the equation to adjust readings from the probe.
      - It will follow the form:
        - y = mx + b
        - where x = raw value
        - y = corrected value
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