Trace Moisture Hygrometers

NIST Low Frost Point Generator (LFPG) Laboratory provides low-humidity calibration and testing services for hygrometers and humidity generators that measure or generate humidity levels between 3 nanomole per mole (nmol/mol, parts per billion, or ppb) of water vapor in nitrogen and 3000 micromole per mole (µmol/mol, parts per million, or ppm).

Hygrometer calibrations are typically performed by subjecting the hygrometer to various H2O/N2 mixtures produced by the NIST LFPG, and comparing the water vapor concentration reported by the device under test (DUT) to that of the LFPG.

n addition to calibration services, NIST provides customized testing services for industries concerned with trace quantities of water vapor in gasses.

The expanded relative uncertainty of water vapor mole fractions produced by the LFPG is 0.8 %, with coverage factor k = 2, plus 0.4 ppb contribution due to outgassing from the sampling system connecting the LFPG to the hygrometer under test.

Devices submitted for calibration or testing must meet the following applicable criteria:

  • Humidity sensing / generation range: The LFPG produces water vapor concentrations between 3 ppb and 3000 ppm of H2O in N2, and frost-point temperatures between -100 ºC and -10 ºC.
  • Sample gas flow rate: The maximum flow rate of test gas produced by the LFPG is 3 standard liters per minute.
  • Tubing connections: Sample gas connections on hygrometers and humidity generators should be metal face-seal, VCR-style fittings.
  • Cleanliness: The proper function of NIST humidity standards requires that internal surfaces of NIST standards and connecting tubing be free of dirt, oil or other contaminants. Submitted hygrometers and generators must be clean.

How to Arrange a Calibration

  1. Contact the staff member in charge of the calibration service for your artifact with any technical or calibration cost questions.
  2. Calibrations are performed on a first come first serve basis.
  3. Ship your artifact with a copy of the purchase order. Use a sturdy box in which we can return the calibrated instrument.
  4. The purchase order my 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 email
  • return shipping method (e.g., shipping account number)

For contact information, shipping address, or cost of calibration, see Humidity Measurements.

Created May 05, 2009, Updated August 25, 2016


  • Technical contact:
    Gregory Scace
    301-975-2626 Telephone
    301-548-0206 Facsimile

    100 Bureau Drive, M/S 8363
    Gaithersburg, MD 20899-8363