3900 Humidity Generator

The Model 3900 Low Humidity Generator is an extremely accurate means of producing known humidity values for calibrating and verifying humidity instrumentation.

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3900 Humidity Generator is based on the combined, NIST proven, fundamental “two-pressure” and “two-temperature” principles, this system will automatically supply a continuous humidified gas stream, within the frost/dew point range of –95.0 °C to 10.0 °C, for days or even weeks unattended.

Simply apply power to the system, and the 3900 will power-up ready to purge and/or generate. Humidity setpoint values are input by the operator from the front panel keypad and are limited only by the operational range of the 3900 humidity Generator.


  • Traceable to NIST
  • Based on NIST Proven Two-Pressure Principle
  • Push Button (Keypad) Control
  • Automated Control of User Setpoints
  • 3900 ControLog® Automation Software
  • HumiCalc® with Uncertainty Software
  • Automatically Applies Enhancement Factors
  • Computerized Internal Transducer Calibration
  • RS-232C Serial Interface
  • Only Nine Square Feet of Floor Space
  • Timed/Formatted Output to Printer
  • Battery Backed-up Real Time Clock
  • Backlit Liquid Crystal Display

Key Specifications

  • Frost Point Uncertainty: * (–70 to 10 °C) 0.1 °C (<–70 °C) 0.2 °C
  • Frost Point / Dew Point Range: –95 to 10 °C
  • Frost Point Resolution: 0.01 °C
  • Parts Per Million Range: 0.05 to 12000 PPMv
  • Relative Humidity Range: 0.0002 to 50%
  • Saturation Pressure Range: Ambient to 300 psiA
  • Saturation Pressure Uncertainty (10-50 psiA): * 0.05
  • Saturation Pressure Uncertainty (50-300 psiA): * 0.30
  • Saturation Pressure Resolution (10-100 psiA): 0.01
  • Saturation Pressure Resolution (100-300 psiA): 0.1
  • Saturation Temperature Range: –80 to 15 °C
  • Saturation Temperature Uncertainty: * 0.08 °C
  • Saturation Temperature Resolution: 0.01 °C
  • Saturation Temperature Heating/Cooling Rate: 2 Minutes Per °C Average
  • Gas Flow Rate Range: 0.1 to 5 slpm
  • Gas Flow Rate Resolution: 0.02 slpm


*Represents an expanded uncertainty using a coverage factor, k=2, at an approximate level of confidence of 95%.

Typical Applications

Virtually any humidity may be generated, for any length of time, within the operational limits of the generator. The output of the device under test may then be compared with the generator’s printed data for analysis.

Chilled Mirror Hygrometers

Connect the generator output to your chilled mirror hygrometer and you can: verify mirror temperature measurement accuracy (calibration) when the hygrometer is in thermal equilibrium with its environment; perform operational checks of the heat pump and optical components, before and after mirror cleaning and balancing; determine whether the hygrometer is controlling the mirror deposit in the liquid phase or ice phase when operating at dew and frost points below 0 °C; determine if the hygrometer is correctly calculating other humidity parameters; determine hygrometer repeatability, stability, and drift characteristics.

Humidity Sensors and Electrolytic Hygrometers

Connect the generator output to your Electrolytic Hygrometer, sampling system, special fixtures, or sensors and you can: determine humidity calibration accuracy and/or characterize humidity sensitivity by subjecting the humidity sensor to a variety of humidity levels; perform operational checks such as the sensing systems capability to correctly calculate and display other humidity parameters; determine repeatability, stability, hysteresis, and drift characteristics of various humidity sensing systems.

Environmental Testing

The 3900 can serve as a test bed for evaluation and R&D of humidity sensors, humidity sensing systems, and humidity sensitive products, e.g., polymers, composites, film, magnetic medium, pharmaceuticals, soil hydrology, consumables, electronics, optics, etc.