CGS-240 Humidity Generator

RH Systems CGS-240 Humidity Generator

Fully Automated Two-Pressure Two-Temperature Humidity Generator

The RH Systems CGS-240 Humidity Generator is a system capable of continuous, high-accuracy humidity generation over a wide range of humidity, temperature, and flow rates. The CGS-240 design is an RHS hybrid two-pressure two-temperature design based on fundamental NIST developed principles

Principle of Operation

A hybrid humidity generator combines the features of the NIST-proven two-pressure and two-temperature humidity generation principles. Utilizing these principles, a stream of gas at an elevated pressure is saturated with respect to the liquid or solid phase of water at a given saturation temperature. Here, saturation temperature is the major determining factor for the quantity of water vapor admixed with the carrier gas. Pressure within the saturator is the major determining factor for the carrier gas quantity of the mixture. Upon leaving the saturator, the humidified gas stream (consisting of the water vapor admixed with the carrier gas) is then expanded to a lower pressure and warmed to an alternate temperature at the point of use, such as a Device Under Test (DUT). Measurements of the pressure and temperature within the saturator, and the pressure and temperature following expansion (generally at the DUT), are then used to determine the resulting humidity content of the gas stream. Humidity is then accurately controlled by regulation of the temperature and pressure within the saturator.

Large, Thermally Uniform Chamber

The chamber utilizes a robust design, with a cable management system for the chamber temperature probe, sample gas injection to the center of an air circulation fan, local pressure measurement, and a multi-position shelving system. It is equipped with high performance thermal insulation surrounding the door and all sides of the test chamber, and features a soft silicone profile seal for perfect tightness. An integrated chamber fan provides internal air circulation which ensures uniformity and stability throughout the working volume.

Thermal Control and Stability

The liquid jacketed chamber door uses heavy duty hinges, a recessed latching mechanism, a built-in light, and integrated heating for the door frame and window. The window inner pane is liquid jacketed and thermally controlled at the same temperature as the chamber to aid significantly in chamber stability and temperature uniformity. The chamber is also liquid jacketed meaning all 6 walls of the chamber are thermally controlled. An air-jacket is then encased within the liquid jacket to ensure unparalleled stability and uniformity.

RHS Control

RHS Control is our custom program allowing the user to operate the humidity generator system from the integrated touch screen monitor. The system may be operated manually through direct entry of desired setpoints, or automatically through a user defined profile. Profiles are a sequence of preprogrammed, user selectable setpoints and dwell times which allow for fully automatic operation and data collection, free of further user intervention.

Data Collection

RHS Control allows for connection of various instruments via digital communication for continuous monitoring, control, and associated data collection. Many instruments with RS-232 or RS-485 communication capability require only an RHS or user-written description file (.json file) to enable data monitoring and collection. Collected data is viewable both numerically and graphically. All data from the CGS-240 and any connected instruments may be viewed together on a common graph. Data is automatically stored to files during collection for later import to Excel and other post process analysis and graphing programs

Hybrid Two-Pressure Two-Temperature Design

In competitor‘s two-pressure designs, the saturator and chamber share a common temperature. While simpler in mechanical implementation, a distinct disadvantage of those basic two-pressure methods is that low humidity generation requires excessively high saturation pressure. This high pressure requirement constrains system design while adding greater burden on air compressor systems.

In contrast, the CGS-240 hybrid design exploits combined capabilities of both the two-pressure and twotemperature principles where the saturator and chamber temperatures are controlled independently of each other. Operating at a lower saturation temperature results in diminished pressure requirements as compared to basic two-pressure systems. This CGS-240 hybrid design allows for a larger humidity generation range with only modest pressure requirements.

Regardless of whether the saturator and chamber are operated at a common temperature using only the two-pressure method, or independently from each other using our hybrid method, humidity calculations such as %RH, Dew Point and others rely on only four measured parameters; two absolute pressures (Psaturation, Pchamber) and two temperatures (Tsaturation, Tchamber). Uncertainty in humidity is determined from the uncertainty in these four measured parameters.

Continuous Run Time

The CGS-240 may run continuously without the need to shut-down; the only requirement being that sufficient water level is maintained in the 20 liter (5 gallon) distilled water reservoir. The reservoir may be filled at any time without the need to stop the system, thereby allowing uninterrupted generation of humidity for days, weeks, or months. The only expected limit to operational run time is when chamber or saturation temperatures operate below 0°C (32 °F) where water freezing within the saturator will temporarily limit gas flow due to eventual ice blockage. In the event of blockage, the simple remedy is to warm the system above freezing for a short period to allow the blockage to melt away. While a saturator bypass circuit is utilized to extend run-time under these expected icing conditions, a limit of approximately 8-12 hours of continuous sub-zero run time is typical before warming is needed.


We reserve the right to change design or technical data without notice.


Generating Range:
Relative Humidity 10…95 %RH (5 %RH optional)
Dew/Frost Point -25…70 °C DP, -23…0 °C FP
Chamber Temperature -0…72 °C (-10 & +85 °C extended ranges optional)
Chamber Pressure Ambient
Flow Rate 5…20 SLPM (5…50 SLPM optional
Accuracy: (0 to 70°C, 10 to 40 l/min)
Relative Humidity The larger of ±0.1 %RH or ±0.5% of indicated RH value
Dew/Frost Point ±0.10 °C
Temperature (TS, TC) ±0.030 °C
Pressure ±0.02% of full scale
Chamber Temp Uniformity <0.035 °C
Flow Rate ±1 SLPM
Integrated Sensors: Cal Range: Cal Uncertainty:
Low Range Pressure (PL) Ambient…25psia ±0.005 psia
High Range Pressure (PH) Ambient…150psia ±0.030 psia
Saturator Temperature (TS) -15…72 °C ±0.03 °C
Chamber Temperature (TC) 0…72 °C ±0.03 °C
Chamber Liquid Temp (TCL) 0…72 °C ±0.10 °C
Presaturator Temp (TP) 0…75 °C ±0.10 °C
Flowmeter 0…50 SLPM ±1 SLPM
Dimensions 15”H x 12”W x 12”D (380 x 300 x 300 mm)
Type Circulating air-jacket encased within liquid jacket
Adjustable Shelf Three shelf positions, one shelf supplied
Access Ports Three 50 mm diameter thermally controlled access ports
Window Size 14”H x 12”W x 12”D (370 x 300 x 300 mm)
Window thermal control Liquid jacketed, multi-pane, thermally controlled
Chamber light Integrated light with on/off touchscreen control
Integrated Control Interface:
Operation Software RHS Control Software
Calibration Software RHS Plateau Software
Display 18.5” Multi Touch Monitor with pinch/zoom/drag
Gas Inlet Pressure:
Using external pressure source 175 psig max
Using supplied air compressor 60…90 psig @ 20 l/min typical
Environmental Conditions:
Operating Environment 15…30 °C, 20…60 %RH
Storage Environment 0…50 °C, <95 %RH non-condensing
Power Requirements:
Voltage 208…240 VAC, 50/60 Hz, single phase
Current 20 Amps