The NIST Hybrid Humidity Generator (HHG) Laboratory provides calibration services for a variety of humidity–measuring instruments. Calibrations are performed by subjecting the instrument under test to air with an accurately known moisture content produced by the generator.
The HHG generates frost/dew points from –70 °C to +85 °C (mole fractions from 1×10E-6 to 0.57) using calibration gas flows up to 150 standard liters per minute. 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, mole fraction, or mass ratio.
For the case of relative humidity calibrations, a separate calibration of the instrument's external temperature probe is performed by means of comparison against a standard thermometer. The instruments and ranges of calibration include but are not restricted to:
- Chilled-Mirror Hygrometers, calibrated at customer-specified points over the dew/frost range of –70 °C to +85 °C, or alternatively over the relative-humidity range 5% to 100% for temperatures between -45 °C and 85 °C.
- Aluminum-oxide Hygrometers, calibrated at customer-specified points over the dew/frost range of –70 °C to +85 °C.
- Electrolytic Hygrometers, calibrated at customer-specified points over a volume-ratio range of 10E–6 to the upper limit of the hygrometer.
- Cavity Ring-Down Hygrometers, calibrated at customer-specified points over a volume-ratio range of 10E–6 to the upper limit of the hygrometer.
For dew/frost point temperatures, the uncertainty budget yields a total expanded uncertainty (k=2) of less than 0.025 °C for dew/frost point temperatures above –60 °C.
For mole fraction, the budget yields a total expanded relative uncertainty of less than 0.2 % for mole fractions above 2 ×10E-5.
How to Arrange a Calibration
- Contact the staff member in charge of the calibration service for your artifact with any technical or calibration cost questions.
- Calibrations are performed on a first come first serve basis.
- Ship your artifact with a copy of the purchase order. Use a sturdy box in which we can return the calibrated instrument.
- The purchase order may be sent to contact by e-mail, fax, or mail. Please include the following information:
- service ID for the calibration
- model and serial number of your artifact
- customer contact name, address, phone, and e-mail
- return shipping method (e.g., shipping account number)
For contact information, shipping address, or cost of calibration, see Humidity Measurements.