Specifications

59
EASY AND RELIABLE CALIBRATION
No measuring instrument stays accurate by itself. It
is essential that the functioning of an instrument is
checked against a reference from time to time.
Vaisala has developed the Humidity Calibrator HMK
15 to make calibration and spot checking of humid-
ity probes and transmitters easy and reliable.
The operating principle of the HMK 15 is based on
the fact that a saturated salt solution generates a
certain relative humidity in the air above it. The
reading of the humidity probe or transmitter can
then be adjusted accordingly. This is a generally
accepted and reliable method for calibrating humid-
ity instruments - many leading laboratories use this
method. Usually two or three different salt solutions
are used which are chosen according to the applica-
tion.
The structure of the HMK 15 is designed to ensure
fast and stable temperature equilibration. No
external power is required. In addition to laboratory
use, it is also suitable for on-site checks. Special
transit covers make the HMK 15 particularly simple
to transport. These features, together with the pre-
measured salts with a long life-span (even after
taken into use), make the HMK 15 the ideal choice
for the most demanding user.
The calibrator can be ordered with certified salts. A
sample calibration is made from each batch in
Vaisalas Measurement Standards Laboratory (MSL).
The uncertainties achieved using these salts at e.g.
+20 °C are given here:
 LiCl salt, 11 %RH (±1.3 %RH)
 MgCl
2
salt, 33 %RH (±1.2 %RH)
 NaCl salt, 75 %RH (±1.5 %RH)
 K
2
SO
4
salt, 97 %RH (±2.0 %RH)
HMK 15 includes a thermometer which is used for
measuring the temperature during the calibration,
and can also be used for checking temperature
measurement accuracy of the transmitter. The
accuracy of the thermometer is ±0.54°F (±0.3°C).
Each thermometer has been calibrated in Vaisalas
Measurement Standards Laboratory (MSL).
HMK 15 Humidity Calibrator
Vaisalas Measurement Standards
Laboratory is a FINAS accredited
calibration laboratory. FINAS is a
member of the EA (the European
co-operation for Accreditation).
HMK 15