Description

DESCRIPTION

The 2900 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 relative humidity, dew point, frost point, parts per million, or other calculated values for instrument calibration and evaluation as well as for precision environmental testing. This system will automatically generate manually entered humidity and temperature set points as well as user created multipoint profiles. All desired humidity’s, temperatures, flow rates, and time intervals may be programmed.

 

PRINCIPLE OF OPERATION

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 is dependent on the measurement of temperature and pressure, not on the amount of water vapor measured in the air. System uncertainty is determined by the temperature and pressure uncertainties, and on the stability and uniformity of the measurements. When setpoint equilibration has been reached, the indication of saturation temperature, saturation pressure, test temperature, and test pressure, are used in the determination of all hygrometric parameters.

 

COMPUTER/CONTROL SYSTEM

The 2900 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 running ControLog.

ControLog is an embedded software application that fully automates the operation of the 2900 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 settings like, pressure, temperature, and flow units. Other settings are °C, °F, atm, Pa, hPa, kPa, L/min, L/hr, cfm and cfh. Humidity is calculated and displayed in percent relative humidity (%RH). 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: The 2900 humidity generation system incorporates a water/glycol jacked test chamber for extremely stable temperature control. Chamber temperature from -10 °C to 72 °C is controlled using PID (proportional-integral- derivative) algorithms to control the temperature of the water/ glycol that jackets the test chamber and associated components. The water/glycol is circulated at the rate of approximately 14 gallons per minute by a magnetically coupled centrifugal pump providing the temperature conditioning of these components, resulting in excellent stability and uniformity for stable humidity generation.

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 humidity generator employs an integrated software calibration scheme allowing the 2900’s probes and 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 2900 humidity generating system incorporates a test chamber, with internal dimensions of 12” x 12” x 10”. Test chamber pressure range is ambient. Access is available
through two 1.875” diameter ports located on the right side.
An externally driven, variable speed, chamber fan is incorporated into the rear wall of the test chamber to reduce thermal gradients. The test chamber accommodates various solid-state sensors, sensing systems, chilled mirror hygrometers, as well as material samples for environmental testing. Virtually any humidity and temperature may be generated, for long periods of time, within the operational limits of the generator. The output or recording of the device under test may then be compared with the generator’s data for analysis.

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