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Easy and ReliableC a l i b ration with theHMK 15 HumidityC a l i b ra t o r
No humidity instru-ment stays accurate onits own. From time totime, the perf o r m a n c eof these instrumentsmust be ch e cke da gainst a reference.When calibration isdone in-house, the useof saturated salt solu-tions as a reference isa proven and afford-able method. Wi t hVa i sala’s HMK 15humidity calibratorhumidity calibration iseasy and reliable.
T
he use of sa t u r a t e dsalt solutions is anaccepted and reli-able method for cali-brating humidity instruments.M a ny leading laboratories usethis method, which has beengenerally known since the early19 0 0 s. The operating principleis basedon the properties ofsalt and water solutions, whichgenerate a known relativehumidity in the air abovet h e m.Based on these reference v a l u e s, the reading of the humid-ity instrument can then beadjusted and calibrated. Satu-rated salt solutions provide areliable measurement standardas the humidity levels generat-ed by these solutions and theirbehavior at different tempera-tures are well documented andhave been verified by many re-s e a r ch e r s. The Greenspan table( Table 1) is one of the mostw e l l -known references.Several different salts aresuitable for reference measure-m e n t s, providing a number ofoptions for the user. With highquality instruments, however,no more than two referencepoints are needed to adjust themeasurement over the entirerelative humidity range. Jan Grönblad, M. S c. (E n g. )Product ManagerSensor Systems DivisionVa i sala HelsinkiF i n l a n d
Ready-dosed saltpackages come withcalibration certificates
Other new additions include sa l tp a ckages with calibration cer-tificates from an accredited la-b o r a t o ry. Examples of the sa l tsolutions suitable for the HMK 15calibrator include lithium ch l o-ride LiCl (11% RH), magne-sium chloride MgCl
K08
(EN45001)(ISO/IEC Guide 25) 2 ( 3 3 %RH), sodium chloride NaCl( 75% RH) and potassium sul-phate K
Vaisala’s Measurement Standards Labo ratory at the Vaisala headquarters inHe l s i n k i, Finland, is a FINAS accredited calibration fa c i l i t y. For morei n f o r m a t i o n, please visit w w w. e u ro pe a n-a c c re d i t a t i o n. o r g 2 SO
4 ( 97% RH). Allthese salts are delivered fromthe factory in dry format toavoid any problems that mayoccur with ready-made salt so-l u t i o n s. Dry salts also offer am u ch longer storage life thanr e a d y -mixed salt solutions. The ready-dosed salt pack-
Shortened thermal andhumidity stabilizationt i m e
During the development of theHMK 15, Va i sala’s latest humid-
i t ycalibrator based on sa t u r a t e dsalt solutions, the main goalswere to improve the ease of useand reliability of the system. Th es h o rtened thermal and humiditystabilization time of the HMK 15 ,w h i ch is one of the main im-provements in the new design,speeds up calibration andimproves the reliability of ther e s u l t s. By combining an alu-minum chamber and properm e chanical design, the sa l tchamber is optimized for fasttemperature stabilization. Th einner space of the chamber isshaped to promote fast humid-ity stabilization and the genera-tion of a homogenous atmos-phere above the salt solution.
18 148/1998