Thunder Scientific 2500 Humidity Generator

Thunder Scientific 2500 humidity generators have set the standard for humidity calibration for over 25 years.  Its classic design, quality manufacturing and innovative application of fundamental metrology has enabled a step forward in humidity measurement precision.

It continues to be a relevant option for calibration laboratories because of its wide generation range, precision and stability.  If your objective is to achieve better humidity calibration uncertainty and you don’t have a 2500, check what other labs are using.

Qrometric have 25 years of experience with the use, calibration and maintenance of the Thunder Scientific 2500 humidity generator.  We can supply, calibrate, service and maintain in the UK and Ireland.  We’re proud to be associated with this fine product.

Thunder’s web pages are current and comprehensive but if you need more information or support, please get in touch on 0207 099 5807 or use the Qrometric contact page.

Qrometric offer a Thunder 2500 service package too. Click on the link for details.

  • Two pressure one temperature principle
  • Precise and stable
  • Self contained and mobile
  • 2500 ControLog®
  • Automated Control of User Setpoints
  • HumiCalc® with Uncertainty Software
  • Computerized Internal Transducer Calibration
  • Low Noise Air Compressor with Air Dryer
  • RS-232C Serial Interface


Almost every new 2500 in the past 10 years has been the Stretched and Tall version. More useful working volume and significant performance upgrades are possible.


Sometimes designated R or S.  Smaller but still a useful volume and it saves $6K

  • Relative Humidity Range: 10 to 95 %RH
  • Relative Humidity stability ±0.1 %RH
  • Chamber Temperature Range: 0 to 70 ºC
  • Chamber Temperature Range: (Optional) –10 to 70 ºC
  • Chamber Temperature Uniformity: ±0.1 ºC
  • Chamber Temperature Stability 0.01 ºC
  • Chamber Pressure Uncertainty: 0.15% FS
  • Chamber Pressure Range: Ambient
  • Display Resolution: 0.01
  • Gas Flow Rate Range: 5 to 20 L/min
  • Gas Flow Rate Resolution: 0.02 L/min
  • Gas Flow Rate Uncertainty: 2% FS
  • Gas Type: Air or Nitrogen
  • Gas Pressure Rating (MAWP): 175 psiG
  • Heating: Stainless Steel Immersion Heater
  • Heating/Cooling Rate: 2.5 Minutes Per ºC Average
  • Cooling: 1/3 hp R-134A Refrigeration System
  • Chamber Window: 6″ x 6″ (152 mm x 152 mm)

The fluid jacketed test chamber can accommodate humidity sensors, hygrothermographs, chilled mirror hygrometers and various material samples for environmental testing. Virtually any humidity and temperature point 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.

Humidity Sensors And Chart Recorders: Insert humidity probes through the two inch port in the side of the chamber or place hygrothermographs into the chamber and you can: determine humidity calibration accuracy and characterise humidity sensitivity by subjecting the sensing system to a variety of humidity levels; perform operational checks such as the sensing systems capability to correctly calculate and display other humidity parameters; determine the repeatability, stability, hysteresis and drift characteristics of various humidity sensing systems.

Chilled Mirror Hygrometers: Install the actual chilled mirror head into the chamber or insert a sample tube through the test port and draw a sample through the chilled mirror head 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 the hygrometer’s repeatability, stability, and drift characteristics.

Environmental Testing: The 2500 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, blood gas analysis, pharmaceuticals, soil hydrology, consumables, electronics, optics, etc. Depending on the temperature and humidity being generated, the 2500 may operate continuously from hours to months. With continuous generation of a nominal 50 %RH at 21 °C, the reservoir will last about two weeks between refills.

Option TPA – Chamber with 3 access ports (2x Ø 48 mm and 1x Ø 6 mm / ¼”)
Option FTP – SPRT access for measurement of the saturation temperature
Option LT – Expanded chamber temperature range of -10 °C to +70 °C
Option MPD – Chamber door with 6 access ports (Ø 28.5 mm)
Option NWD – Chamber door without window
Option CIS – Chamber instrument shelf
Option CFM – Chamber Fixture Mount
Option QPW – Chamber door with window and 4 access ports (Ø 28.5 mm)
Option FCD – Fluid Jacketed Shelf Divider
Option FSB – Chamber with connections for thermostated fluid
Option TCD – Temperature Controlled Door
Option F40 SLPM – Higher gas flow rate (from 20 to 40 slpm)