The Model 1200 Mini Humidity Generator produces extremely accurate humidity values using the fundamental, NIST proven, "two-pressure" principle. The 1200 will automatically supply relative humidity, dew point, frost point, or other calculated values for instrument calibration and evaluation as well as precision environmental testing. This system will automatically generate multipoint profiles as well as manually entered humidity levels, while continuously storing and printing system data.

Virtually all functions of the 1200 humidity generator are computer controlled. All desired humidities, temperatures, and time intervals may be programmed. Visual indications of system status are displayed in real time on the computer screen. The automated features of the 1200 allow the generation of known humidity levels completely unattended. This frees the operating technician from the task of monitoring and adjusting.

The "two-pressure" humidity generation process involves saturating air or nitrogen with water vapor at a known temperature and pressure. The saturated high-pressure air flows from the saturator, through a pressure reducing valve, where the air is isothermally reduced to test pressure at test temperature. Humidity generation by the 1200 does not depend upon measuring the amount of water vapor in the air, but rather is dependent on the measurements of temperature and pressure alone. System precision is determined by temperature and pressure measurement accuracy, and on the constancy of the measurements throughout. When setpoint equilibration has been reached, the indication of saturation temperature, saturation pressure, test temperature, and test pressure, may be used in the determination of all hygrometric parameters.

Computer / Control System

The Computer/Control System performs all control functions required for humidity generation, as well as displaying, printing, and storing system parameters in real time. The computer/controller is made up of several main components, each with individual yet cooperative functions. The Computer/Control System utilizes a Windows based computer system that is used to read transducers and temperature sensors; supply digital outputs for control of temperatures, pressures, and mass flow; and control relay outputs for control of system power, heaters, heat pump and circulation pump.

Temperature Control: The system utilizes solid-state thermoelectric (Peltier) cooling/heating and a fluid jacketed test chamber for extremely stable temperature control. Temperature setpoint control is attained by controlling the temperature of a circulating fluid medium that jackets the test chamber and associated humidity generation components. Chamber and saturation temperatures are governed by this medium and are digitally controlled by the computer at any value between 10 °C and 60 °C using PID (proportional-integral-derivative) algorithms. This allows a very stable humidity to be generated.

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. The 1200 employs an integral programmatic calibration scheme allowing the transducers to be calibrated while they are electrically connected to the humidity generator. Coefficients for each transducer are calculated by the computer and stored to memory.

Test Chamber

The test chamber accommodates various solid-state sensors, data loggers, chilled mirror hygrometers, and material samples for environmental testing. The 1200 humidity generating system incorporates a 300 series stainless steel fluid jacketed test chamber, with internal dimensions of 6" x 6" x 6" (152 mm x 152 mm x 152 mm). Access is available through a 1.625" (41.3 mm) diameter port on the right side for probes, cables, sample tubes, etc.

Applications

Virtually any humidity and temperature may be generated within the operational limits of the generator. The output or recording of the device under test may then be compared with the generators data for analysis.

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 hygrometers repeatability, stability, and drift characteristics.

Humidity Sensors and Data Loggers: Insert your humidity probes through the chamber access port or install the data logger into the chamber 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 the repeatability, stability, hysteresis, and drift characteristics of various humidity sensing systems.

Environmental Testing: The 1200 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.