Prepare the salts using the equipment provided with the calibrator or make sure that all accessories used are suitable for preparing salt solutions and are absolutely clean. If necessary, wash them carefully and rinse several times before preparing the salt solutions. The last rinse must be made with distilled or ion exchanged water.
The salts are quick and easy to prepare with the ready-dosed salt packages available from Vaisala. If you do not use ready-dosed salt packages, measure the salts using the measurement cup provided. Make sure that the cup is clean before measuring the salts. The salt solutions must be prepared from pro analysis grade salts, which are available in agencies selling industrial chemicals. Note that the water must be distilled or ion exchanged (conductivity < 0.25 µS/cm). You can order ion exchanged water as an accessory for the HMK15 calibrator (item code 19767HM).
Handle the salts and equipment carefully and keep them absolutely clean so that the salts are not contaminated. Make sure that the salts do not mix.
There must not be more than 10 mm (0.39 in) of undissolved salt and liquid at the bottom of the salt chamber. Otherwise, the sensor to be calibrated may get immersed into the solution. If necessary, verify the amount, for example, with the measurement spoon.
The use of saturated salt solutions is covered by several standards, including ASTM E104 - 20a and JIS Z 8806.
Some salts in the ready-dosed salt packages, especially potassium chloride, may harden slightly over time. This may happen even with the vacuum bag intact. Before using a salt bag with hardened salt inside, break up the salt with, for example, a small rubber mallet. Shelf life of unopened salt bags is 2 years.