Atmos Wiki

• Description: Calibration set up for Vaisala Humidity Sensors
• Manufacturer: Vaisala
• Manufacturer Spec Site: Vaisala HMK15 Humidity Calibrator
• Model: HMK15
• Manual: HMK15 User Guide

• Main Board
  • Salt Solution Chambers (x2)
  • Sensor Cap Attachment (x2)
  • Sensor Cap Plugs (x10)
  • Thermometer
• Measuring Cup
  • 
• Plastic Probe/Stirring Stick
  • 
• Adapter Rings (x3)
  • 
• Salts
  • 
  • 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
  • 
• Certificate of Calibration/Inspection
  • 

Need:

• HMK15 Humidity Calibrator
• Vaisala Humidity Sensor
• Deionized water

Steps:

1. Prepare salt solutions
   1. Take the calibrator out of the box and place it on a clean, even surface.
   2. Remove the transit cover of the salt chamber.
   3. Remove the chamber lid from the chamber holder and put it aside.
   4. Press the transit cover on the chamber holder.
   5. Pour the required amount of ion exchanged water into the salt chamber.
      1. LiCl: 12 ml
      2. MgCl2: 3 ml
      3. NaCl: 10 ml
      4. KCl: 10 ml
      5. K2SO4: 10 ml
   6. Sprinkle the contents of a salt package (or measure the required amount of salt 1) in small quantities into the chamber, stirring constantly.
      1. LiCl: 15 g / 18 ml
      2. MgCl2: 30 g / 30 ml
      3. NaCl: 20 g / 15 ml
      4. KCl: 30 g / 30 ml
      5. K2SO4: 30 g / 20 ml
   7. When measuring with the measurement cup, make sure that the cup is clean and dry. Rinse and dry the cup after every use.
   8. 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.
   9. Close the salt chamber with the chamber lid.
   10. Fasten the salt chamber on the holder in the base plate and close the measurement holes with rubber plugs.
   11. The chambers can also be used individually, without the base plate.
   12. 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.
   13. Keep the holes always closed when not calibrating.
   14. 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.
   15. Allow approximately 24 hours for stabilization before use so that the salt solution reaches the equilibrium humidity.
   16. 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.
2. Calibrate Instrument
   1. Remove the cover from the end of the thermometer and flip it around the other way.
   2. Complete the following steps twice, once for each solution
      1. Insert the thermometer into the largest hole of the calibration cover of the solution.
      2. Remove the cover on the probe and insert into the calibration cover.
      3. Wait for the reading to stabilize, and record both the humidity reading and the temperature
         1. This could take 10-30 minutes
   3. Repeat for the second solution.
3. Adjust instruments
   1. Using the values you recorded and the following table, find the equation to adjust readings from the probe.
      1. It will follow the form: