NDLI: A Simple Humidity Generator for Relative Humidity Calibrations

Content Provider	Springer Nature Link
Author	Liedberg, H. G. Mnguni, M. R. Jonker, D.
Copyright Year	2008
Abstract	At present, the South African national humidity measurement standards, maintained by NMISA, consist of two chilled-mirror hygrometers operating from (−75 to 20) °Cdp and unsaturated salt solutions covering the range (5 to 95) %rh. To reduce measurement uncertainties and to obtain traceability to local measurement standards for temperature and pressure, it is desired to replace the salt solutions by a dew-point generator for relative humidity calibrations from (5 to 95) %rh (5 to 60) °C, equivalent to a dew-point range of (−30 to 59) °Cdp. Required uncertainties in relative humidity (at a coverage factor of k = 2) are (0.1 to 1.2) %rh. This article describes the design and evaluation of a two-pressure humidity generator intended to satisfy this requirement. The saturator consists of a coil of stainless steel tubing immersed in a 70 l stirred water bath. Pressure reduction is accomplished using a throttling valve adjusted by a stepper motor, and hygrometers being calibrated are sealed into a small test chamber contained in a larger temperature-controlled chamber. The results of the following performance tests are presented: (i) comparison of the output when the air stream was oversaturated before entry to the saturator to that when it was dry, (ii) comparison with a chilled-mirror hygrometer from (−25 to 20) °Cdp, and (iii) comparison with relative humidity hygrometers that had previously been calibrated against salt solutions.
Starting Page	1660
Ending Page	1667
Page Count	8
File Format	PDF
ISSN	0195928X
Journal	International Journal of Thermophysics
Volume Number	29
Issue Number	5
e-ISSN	15729567
Language	English
Publisher	Springer US
Publisher Date	2008-05-21
Publisher Place	Boston
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Calibration Dew point Humidity generator Relative humidity Physical Chemistry Industrial Chemistry/Chemical Engineering Mechanics Condensed Matter
Content Type	Text
Resource Type	Article
Subject	Condensed Matter Physics

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