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Thermodynamic Quantities

Humidity Measurements

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Technical Contacts:

Christopher Meyer
Tel: 301-975-4825
E-mail: cmeyer@nist.gov   

Gregory E. Scace
Tel: 301-975-2626
E-mail: gregory.scace@nist.gov

Please contact the technical staff before shipping instruments or standards to the address listed below.

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 (Dew/Frost point only) 
Range: -70 ºC to 85 ºC

Relative Humidity Hygrometers (RH sensors and psychrometers),
Range: 3% to 98% at temperatures from 5 ºC to 85 ºC

36030C External Temperature Probe for Dew-point Hygrometer (enabling RH measurements)
Range: –110 ºC to 150 ºC
36040C Electrolytic Hygrometers 235/point
36070S Special Tests of Humidity At Cost

Fees are subject to change without notice.

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Hygrometers (36010C-36040C)

NIST provides calibration services for a wide variety of humidity-measuring instruments. Calibrations are performed by subjecting the device under test (DUT) to air with accurately known moisture content (mole fraction) produced by the generator. For dew/frost point calibrations, the pressure of the air at the inlet of the hygrometer is measured for calculation of the dew/frost point temperature of the air at that location. For relative-humidity calibrations, the DUT is placed in a test chamber controlled at an accurately-known temperature, where the air from the generator is directed; the known moisture content of the air, combined with measurements of the pressure and temperature, provide the relative humidity in the location of the DUT.

The HHG generates dew-point temperatures TDP and frost-point temperatures TFP from –70 °C to +85 °C (mole fractions from 2.6×10−6 to 0.57) using calibration gas flows up to 150 standard liters per minute. Note: temperatures at or above 0 °C are dew-points and temperatures below 0 °C are frost-points. The HHG combines the two-pressure and divided-flow humidity generation techniques (hence the name "hybrid").The calibrations may be performed using humidity definitions of dew/frost point, relative humidity (RH), or mole fraction.

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Special Tests of Humidity (36070S)

Tests for response time, hysteresis, and stability can be provided upon request.

Table 2. Uncertainty of calibrations using the NIST Hybrid Humidity Generator, including repeatability of a state-of-the-art device under test.

Humidity Parameter Range Expanded Uncertainty

Dew/frost point temperature TDP, TFP ( °C)

–70 °C < TFP < –40 °C

0.11 °C

–40 °C < TFP < –15 °C

0.07 °C

–15 °C < TFP, TDP < 85°C

0.04 °C

Relative humidity, RH at test chamber temperatures of 2 °C to 85°C

3% < RH < 0.98%

1 %

Mole fraction

2.5×10-6  < x < 0.03

0.2 % of value

0.03 < x < 0.57

0.1 % of value

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References-Humidity Measurements

C.W. Meyer et al., Calibration of Hygrometers with the Hybrid Humidity Generator, NIST.

G.E. Scace et al., The New NIST Low Frost-Point Humidity Generator, presented at the 1997 NCSL Workshop and Symp., Atlanta, GA (1997).

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Program questions:
Phone: 301-975-5454, Fax: 301-975-2950
NIST, 100 Bureau Drive, Stop 8363, Gaithersburg, MD 20899-8363