Gregory E. Scace
Please contact the technical staff before shipping instruments or standards to the address listed below.
National Institute of Standards and Technology
Fees are subject to change without notice.
NIST provides calibration services for a wide variety of humidity-measuring instruments. Calibrations are performed by subjecting the instrument under test to atmospheres of known moisture content produced by the NIST two-pressure humidity generator. The instruments and ranges of calibration are listed below:
A. Dew-Point Hygrometers calibrated over the dew/frost range of -70 °C to +60 °C.
B. Electric Hygrometers classified under this category are sensors which sorb water vapor as a function of relative humidity; associated with this sorption is a corresponding change in an electric parameter (that is, resistance, capacitance). The range of calibration is 3 % to 98 % relative humidity over the temperature range -55 °C to +40 °C.
C. Psychrometers are wet-dry bulb hygrometers (aspirated psychrometers). The contact person should be consulted for the special features of the psychrometer which are necessary in order that the instrument can be calibrated at NIST.
D. Electrolytic Hygrometers are devices which electrolyze water into gaseous oxygen and hydrogen by the application of a voltage in excess of the thermodynamic decomposition voltage for water, and then measure the electrolysis current. The range of calibration in volume ratio is 10-6 to 3 x 10-2.
E. Pneumatic Bridge Hygrometers are instruments that measure the variation of the pressure drop across two combinations of nozzles, operating at critical flow, with a desiccant between one pair of nozzles. The range of calibration in mixing ratio (grams of water vapor/grams of dry air) is 0.0005 to 0.015. Table 6.5 illustrates typical NIST uncertainties for measurement of humidity standards with atmospheric air at atmospheric pressures.
Tests for response time, hysteresis, and stability can be provided upon request.
Table 6.5. NIST Two-Pressure Humidity Generator, Mark 2, Range and Uncertainty
The New NIST Low Frost-Point Humidity Generator, G. E. Scace, P. H. Huang, J. T. Hodges, D. A. Olson and J. R. Whetstone, presented at the 1997 NCSL Workshop and Symp., Atlanta, GA (1997).
Thermodynamic Properties of Moist Air Containing 1000 to 5000 PPMv of Water Vapor, P. H. Huang, NISTIR 5241, 43-51 (Apr. 1993).
NIST Calibration Services for Humidity Measurement, P. H. Huang, NISTIR 4677-A (Superseding NISTIR 4677, Oct. 1991).
National Basis of Accuracy in Humidity Measurements, S. Hasegawa, ISA Trans. 25 (3), 15-24, 1986.
The NBS Two-Pressure Humidity Generator, Mark 2, S. Hasegawa and J. W. Little, J. Res. Nat. Bur. Stand. (U.S.), 81A (1), 81-88 (Jan.-Feb. 1977).Calibrations Phone: 301-975-2200, Fax: 301-975-2950 NIST,