Thunder Scientific Corporation - Humidity Generation and Calibration Equipment NVLAP - Code 200582-0

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Toll Free: (800) 872-7728
Phone: (505) 265-8701
FAX: (505) 266-6203



NEW Product

Model 3920 Automated Low Humidity Generator.

Model 3920

Automated Low Humidity Generation System



  • Traceable to SI 1
  • High Flow Capability of 10 L/min
  • Based on NIST Proven "Two-Pressure" Principle
  • HumiCalc® with Uncertainty Mathematical Engine
  • ControLog® Embedded Automation Software
  • Generate: Frost Point, Dew Point, PPM, %RH
  • Calculated Real-Time Uncertainty
  • Multi-point Touch LCD
  • Additional Keyboard Interface
  • Calculated Water Capacity to Indicate Water Usage


The Model 3920 Low Humidity Generation System is a self-contained system capable of producing atmospheres of known humidity using the fundamental “two-pressure” principle. This system is capable of continuously supplying frost point, dew point, parts per million, relative humidity and other calculated values for instrument calibration and evaluation as well as for precision environmental testing. This system will automatically generate manually entered humidity as well as user created multipoint profiles. Visual indications of system status are displayed in real time on the computer monitor.



The “two-pressure” humidity generation process involves saturating nitrogen with water vapor at a known temperature and pressure. The saturated high-pressure gas is then reduced to test pressure and warmed to test temperature. The indication of saturation temperature, saturation pressure, test temperature, and test pressure is used in the determination of all hygrometric parameters. Humidity generation by this system does not depend upon measuring the amount of water vapor, but it is dependent on the measurements of temperature and pressure alone. The precision of the system is determined by the accuracy of the temperature and pressure measurements and on the constancy of them throughout.



Elemental Schematic of the 3920 generator.
Elemental Schematic of the 3920 generator.


Control / Display Screen

The 3920 Low Humidity Generation System encompasses a high-performance stand-alone Control System that performs all functions required for humidity generation and control. The Control System employs 24 bit I/O modules with integrated signal conditioning to acquire data and uses serial interfaces to transducers and stepper motors to control the operation of generating humidity. The Control System utilizes an embedded operating system in conjunction with specialty software to control and interface with the human to machine interface (HMI) computer that runs Thunder's automation software called ControLog.


ControLog is an embedded software application that fully automates the operation of the 3920 Low Humidity Generation System and allows various device connections through a number of different interfaces. ControLog uses Thunder Scientific’s HumiCalc with Uncertainty as its mathematical engine for computing all humidity values and real-time uncertainties. Data from the generator and attached devices is automatically retrieved and stored for viewing in either numerical or graphical format in real time or post process. Data can be transferred off the system via a USB drive for further viewing, post processing and printing using an external Windows PC. The ControLog software also provides the primary interface to the operator via the multi-point touch LCD which allows the user to select humidity parameters, pressure, temperature, and flow units. The Parameter Tab is the primary interface for the user and is divided in two sections, Control and Calculated Humidity. Within each tab there are two different tiles, the Setpoint Tile is for the user to enter the desired setpoints and a Value Tile displays the Actual Value.


Temperature Control: Temperature setpoint control is attained by controlling the temperature of a circulating fluid medium that jackets the saturator of the generator. The saturation temperature is governed by the temperature of this medium, which is digitally controlled by the computer at any value between –80 °C and 12 °C through the use of PID (proportional-integral-derivative) algorithms.

Pressure And Flow Control: Pressure control and mass flow control are accomplished through computer actuation of electromechanical valve assemblies. Saturation pressure and mass flow are measured continuously and controlled using PID algorithms similar to those employed in temperature control.

Calibration: Proper calibration of the temperature and pressure transducers ultimately determines the accuracy of the generator. This system employs an integral programmatic calibration scheme allowing the transducers to be calibrated while they are electrically connected to the humidity generator.

Water Capacity and Clear-Cyles Screen

Water Capacity and Clear-Cyles Screen



Chilled Mirror Hygrometers: Connecting the generator output to a chilled mirror hygrometer allows the user to verify the mirror temperature measurement accuracy; perform operational checks on the hygrometer components; determine whether the hygrometer is controlling the mirror in the liquid phase or ice phase when operating 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 a electrolytic hygrometer, sampling system, special fixtures, or sensors allows the user to calibrate and/or characterize humidity sensitivity; 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 3920 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.




Frost Point Temperature Range: –95 to 0.01 °C
Dew Point Temperature Range: –50 to 10 °C
Parts Per Million Range: 0.04 to 12300 PPMv
Relative Humidity Range: 0.00003% to ~50%
Temperature Specification: 0.027 °C
Saturation Temperature Range: 3 –80 to 12 °C
Saturation Temperature Control Stability: 4 0.008 °C
Saturation Temperature Cooling Rate: from 12 to –80 °C 0.33 °C per Minute (average)
Saturation Temperature Heating Rate: from –80 to 12 °C 0.33 °C per Minute (average)
Test Temperature Range (measured): 0 to 50 °C
Saturation Pressure Range: ~Ambient to 250 psiA
Saturation Pressure Specification: 0.02% of full scale
Test Pressure Range (measured): Ambient to 50 psiA
Test Pressure Specification: 0.02% of full scale
Gas Type: Gaseous Nitrogen
Supply Pressure Range: 80 to 300 psiG
Supply Pressure Specification: ±1 psiG
Gas Flow Rate Range: 0.5 to 10 SLPM
Gas Flow Rate Resolution: 0.2 SLPM
Gas Flow Rate Specification: 2% of full scale
Display Resolution: 0.001
Refrigeration: 1/3 HP R-134A & 1/3 HP R-23 in cascade
Heating: Stainless Steel Immersion
Test Port: 1/4 Inch Swagelok VCR®
Physical Dimensions: 37.9" H x 23" W x 34.9" D (965mm x 585mm x 889mm)



2,5 & 6

Dew Point Uncertainty: –50 °C to 10 °C: 0.01% |R| + 0.07 °C
Example: If the dew Point reading is 10 °C. The uncertainty would then be: 0.01% 10 + 0.07 °C = 0.071
Frost Point Uncertainty: ≥ –90 °C 0.05% |R| + 0.07 °C
Example: If the frost Point reading is –60 °C, the uncertainty would then be: 0.05% 60 + 0.07 °C = 0.1
Frost Point Uncertainty: < –90 °C 2% |R| –1.7 °C
Example: If the frost Point reading is –95 °C, the uncertainty would then be: 2% 95 –1.7 °C = 0.2
Test Temperature Uncertainty: 0 °C to 50 °C 0.034 °C

1 Traceable to the International System of Units (SI) through a national metrology institute (NIST) recognized through a CIPM MRA.

2 Test pressure at 1 atmosphere.

3 Using anhydrous methanol as the temperature heat transfer fluid from –80 to 12 °C.

4 Temperature Control Stability is defined as the standard deviation over a 10-minute period, as measured by the saturation temperature control sensor after being at point for 60 minutes.

5 Uncertainty values represent an expanded uncertainty using a coverage factor, k=2, at an approximate level of confidence of 95%.

6 Uncertainty is based on the worst-case value from the 3920 uncertainty analysis



Electrical Power: 200/230 V~, 10 A, 1 Ø, 50/60 Hz
Gas Supply: Min 80 psiG @ 10 L/min - Max 300 psiG @ 10 L/min



Operating Temperature: 15 to 30 °C
Storage Temperature: 0 to 50 °C
Humidity: 5 to 95% Non-condensing



The accessories available for the 3920 are the 4 Port Heated Manifold (4PHM) with controller and comes standard with 3/4"-16 straight thread adapters. This accessory can also be used with the Model 3900 as well. The second accessory available for the 3920 is the New Model ACS3920 Air Compressor System. Ask your sales representative for details.


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