Thermodynamic Quantities Humidity Measurements Technical Contacts:
Peter Huang
Tel: 301/975-2621 or 2626
E-mail: peter.huang@nist.gov Joseph T. Hodges
Tel: 301/975-2605
E-mail: joseph.hodges@nist.gov Gregory E. Scace
Tel: 301/975-2626
E-mail: gregory.scace@nist.gov Do not ship instruments or standards to the mailing address listed below. Contact the technical staff for the shipping address.
National Institute of Standards and Technology
100 Bureau Dr., Stop 8363
Gaithersburg, MD 20899-8363
Fax: 301/548-0206
Service ID
Number | Description of Services | Fee ($) | | 36010C | Dew-Point Hygrometers (+25 ºC to -15 ºC) | 6208 | | 36020C | Dew-Point Hygrometers (-70 ºC to -15 ºC) | 11706 | | 36030C | Electric Hygrometers | At Cost | | 36040C | Electrolytic Hygrometers | At Cost | | 36050C | Aspirated Hygrometers | At Cost | | 36060C | Pneumatic Bridge Hygrometers | At Cost | | 36070S | Special Tests of Humidity | At Cost | Fees are subject to change without notice. back to top | back to index of thermodynamic quantities Hygrometers (36010C-36060C) 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.
back to top | back to index of thermodynamic quantities Special Tests of Humidity (36070S) 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 | Humidity Parameter | Range | Expanded Uncertainty | Mixing ratio, rw
(g water vapor/kg dry air) | 0.0015< rw < 0.005 | 1.5 % of value | | 0.005 < rw < 0.1 | 1.0 % of value | | 0.1 < rw < 0.3 | 0.5 % of value | | 0.3 < rw < 515 | 0.3 % of value | Volume ratio,
V (X 10-6 ) | 3 < V < 10 | 1.5 % of value | | 10 < V < 170 | 1.0 % of value | | 170 < V < 500 | 0.5 % of value | | 500 < V < 820 000 | 0.3 % of value | Dew point temperature,
Td ( °C) | -70 < Td < -35 | 0.1 °C | | -35 < Td < +40 | 0.04 °C | Relative humidity,
RH (%) at test
chamber temperature,
Tc ( °C) of: | -55 < Tc < -40 | 3-98 1.5 % | | -40 < Tc < -20 | 3-98 0.8 % | | -20 < Tc < 0 | 3-98 0.2 % | | 0 < Tc < +40 | 3-98 0.2 % | back to top | back to index of thermodynamic quantities
References-Humidity Measurements 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). back to top | back to index of thermodynamic quantities
Date created: 06/30/1999
Last updated: 01/17/2008 | 