SPECIFICATIONS

UNCERTAINTY ^5,6

¹ Using glycol/water as the temperature bath heat transfer fluid from 0 to 5 °C and water as the temperature bath heat transfer fluid from 5 °C to 72 °C.

² Temperature Control Stability is defined as the maximum deviation from a best fit line, as measured by the bath temperature control sensor. If data is logged digitally, the best fit line will be defined as the average value over the 10 minute period. All measurements made with an insulated cover in place over bath.

³ Chamber Temperature Uniformity is defined as the maximum temperature difference between any two locations over the temperature range of 0 °C to 72 °C when using a thermal insulator over the bath, such as hallow bath balls. Locations are defined at the center of the chamber lid access ports, approximately 5" into the chamber.

⁴ Refer to "Model_9500_Uncertainty_Analysis.pdf" for more information.

⁵ Uncertainty is not specified at flow rates below 10 slpm and above 100 slpm.

⁶ Uncertainty values represent an expanded uncertainty using a coverage factor, k=2, at an approximate level of confidence of 95%.

⁷ Includes saturation temperature, chamber temperature, bath temperature, pre-saturator temperature, and exp-valve temperature.

UTILITIES

ENVIRONMENTAL

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 by the 9500 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.

Elemental Schematic of the 9500 generator.

COMPUTER CONTROL

9500 Main Computer Screen

Control / Display Screen

The Model 9500 Humidity Generator encompasses a high-performance stand-alone Data Acquisition/Computer that performs all functions required for humidity generation and control. The Data Acquisition System employs 24 bit I/O modules with integrated signal conditioning to acquire data and control the operation of generating humidity. The Computer utilizes an embedded based 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 Thunder Scientific 9500 Humidity Generator and allows various device connections through a number of different interfaces. 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 (not included). The ControLog software also provides the primary interface to the operator via the multi-point touch LCD and keyboard.

Temperature Calibration Screen

Temperature Calibration Coefficients Screen

Temperature Controlled Bath: The 9500 humidity generating system incorporates a computer controlled temperature bath. Bath temperature is digitally controlled by the computer at any value between 0 °C and 72 °C using PID (proportional-integral-derivative) algorithms. The test chamber, saturators, heat exchangers, and connecting tubing are immersed in approximately 20 gallons of distilled water that is circulated at the rate of 50 gallons per minute by a magnetically coupled centrifugal pump. Fast fluid circulation provides the temperature conditioning of these components, resulting in long term bath stability and uniformity. 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, chamber 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 9500 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.

9500 Test Chamber

9500 Test Chamber View

The 9500 humidity generating system incorporates a completely immersed test chamber, with internal dimensions of 12" x 12" x 12" (305 mm x 305 mm x 305 mm). Test chamber pressure range is ambient to 20 psiA. The main chamber cover is removable utilizing quick release hold downs. Removal of the chamber cover allows a full 12 inch by 12 inch access to the test space. Access is also available through two 3.65" diameter ports in the chamber cover or two 1.125" inside diameter port cover adapters.

(Shown with the optional 4 Port Chamber lid)

APPLICATIONS

The test chamber can accommodate various solid state sensors, chilled mirror hygrometers, psychrometers, hygrothermographs, and material samples for environmental testing. Virtually any humidity and temperature may be generated, for any length 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 printed 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 heatpump 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 hygrometer’s repeatability, stability, and drift characteristics.

Humidity Sensors And Chart Recorders: Insert your humidity probes through a test port in the chamber or install the hygrothermograph 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 9500 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.

REFERENCE DOCUMENTS

Model 9500 Humidity Generation System Documents

Series 9500 operation and maintenance manual for the automated two-pressure humidity generator.

• 9500 Humidity Generator Manual (11.6 MB)
• Model 9500 Humidity Generator Data Sheet (3.2 MB)

Model 9500 Uncertainty Analysis

This document describes a complete uncertainty analysis of the Model 9500 in accordance with NIST Technical Note 1297. Each error source is identified, quantified, and combined to form an expanded uncertainty using a coverage factor, k=2, at an approximate level of confidence of 95%.

• 9500 Humidity Generator Uncertainty Analysis (1.35 MB)
• 9500 Chamber Temperature Uniformity Analysis (584 K)