Model 2500 Benchtop/Mobile “Two-Pressure” Humidity Generator

Overview

The Model 2500 Benchtop Humidity Generator is a self contained system capable of producing atmospheres of known humidities using the fundamental, NIST proven, "two-pressure" principle. This system is capable of continuously supplying accurately known humidity values for instrument calibration, evaluation, and verification, as well as for environmental testing. Simply apply power and the 2500 will power-up ready to generate. Humidity setpoint values are input by the operator from the front panel keypad and are limited only by the range of the 2500 humidity generator. Relative humidities are calculated from the measurements of pressure and temperature with the formula: %RH= fs/ fc · es/ ec · Pc/ Ps · 100

To generate a known humidity, the computer controls the pressure ratio Pc /Ps utilizing the enhancement factor ratio fs/fc and the effective degree of saturation es/ec. Humidity produced is solely dependent on the measurement of pressures and temperatures and does not rely on any other device (such as a dew point hygrometer, psychrometer, or humidity sensor) for the measurement of water vapor content. Precision humidity generation is determined by the accuracy of the pressure measurements and on the accuracy and uniformity of temperature throughout the generating system.

Features

• Accuracy ± 0.5 %RH
• Traceable to NIST
• Self Contained and Mobile
• Automated Control of User Setpoints
• ControLog TM Automation Software
• HumiCalc ® Humidity Conversion Software
• Computerized Internal Transducer Calibration
• Low Noise Air Compressor with Air Dryer
• RS-232C Serial Interface

Principle of Operation

The Model 2500 Benchtop Humidity Generator operates using an on board multifunction CPU in conjunction with other peripheral cards to perform calculation and control functions. The embedded computer control system allows the 2500 to generate known humidity levels unattended, freeing the operating technician from the task of system monitoring and adjustment. A computer and/or printer may be connected via the bi-directional RS-232C interface ports allowing remote setpoint control and continuous acquisition of system data. Humidity and temperature setpoint values are input by the operator from the front panel keypad while visual indications of system status are displayed in real time on the liquid crystal display.

Control/Display Screen

All control and measurement parameters critical to the operation of the humidity generator are displayed on this screen. Each parameter in the left most column is identified with a brief title and corresponding units. The generator operates in a variety of user selectable pressure, temperature, and flow units. Some of these are °C, °F, psi, "Hg, Tor, mbar, kPa, l/m, l/h, cfm and cfh. Humidity is calculated and displayed in percent relative humidity (%RH). The asterisk in the left most column indicates the active humidity control parameter. The "SetPnt" column lists control setpoints and the "Actual" column lists all of the measured data and calculated parameters of the generator.

Temperature Control

The system utilizes a fluid jacketed test chamber for extremely stable temperature control. Temperature setpoint control is attained by controlling the temperature of the 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 0 °C and 70 °C using PID (proportional-integral-derivative) algorithms.

Pressure And Flow Control

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

Calibration

The 2500 humidity generator employs an integral programmatic calibration scheme allowing the temperature and pressure transducers to be calibrated while they are electrically connected to the humidity generator.

Coefficients for each transducer are calculated by the computer and stored in the system’s nonvolatile memory until the next calibration is performed.

ControlLog^TM

Our ControLog™ software allows you to program a series of humidity and temperature set-points and automatically steps through the set-points to maintain stable calibration conditions. Not only does it automate the control of the 2500, but it also will collect, store, and graph data from all RH Systems products as well as the HP34970A and the Hart 1529 Chub-E4 thermometer. Up to 8 instruments can be connected simultaneously.

Applications

The fluid jacketed test chamber can accommodate humidity sensors, hygrothermographs, chilled mirror hygrometers, and various material samples for environmental testing. Virtually any humidity and temperature point may be generated, for any length of time, within the operational limits of the generator. The output of the device under test may then be compared with the generator's printed data for analysis.

Humidity Sensors And Chart Recorders

Insert humidity probes through the two inch port in the side of the chamber or place hygrothermographs into the chamber and you can: determine humidity calibration accuracy and characterize humidity sensitivity by subjecting the sensing system 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.

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 hygrometer's repeatability, stability, and drift characteristics.

Environmental Testing

The 2500 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, blood gas analysis, pharmaceuticals, soil hydrology, consumables, electronics, optics, etc. Depending on the temperature and humidity being generated, the 2500 may operate continuously from hours to months. With continuous generation of a nominal 50 %RH at 21 °C, the reservoir will last about two weeks between refills.

2500 SpecificationsWe reserve the right to change design or technical data without notice.

TABLE A
Physical Dimensions

MODEL	H DIM	W DIM	D DIM
2500	19" (483 mm)	33" (838 mm)	20" (508 mm)
2500S	19" (483 mm)	36" (914 mm)	20" (508 mm)
2500ST	22" (559 mm)	36" (914 mm)	23" (584 mm)

TABLE B
Physical Dimensions of Cart

MODEL	H DIM	W DIM	D DIM
2500	33.25" (845 mm)	40" (1.02 m)	23" (584 mm)
2500S	33.25" (845 mm)	43" (1.09 m)	23" (584 mm)
2500ST	33.25" (845 mm)	43" (1.09 m)	26" (660 mm)

TABLE C
Physical Dimensions 2500 with Cart

MODEL	H DIM	W DIM	D DIM
2500	53" (1.35 m)	40" (1.02 m)	23" (584 mm)
2500S	53" (1.35 m)	43" (1.09 m)	23" (584 mm)
2500ST	56" (1.42 m)	43" (1.09 m)	26" (660 mm)

TABLE D
Chamber Dimensions

MODEL	H DIM	W DIM	D DIM
2500	12" (305 mm)	12" (305 mm)	10" (254 mm)
2500S	12" (305 mm)	15" (381 mm)	10" (254 mm)
2500ST	15" (381 mm)	15" (381 mm)	12" (305 mm)

TABLE E
Access Port Dimensions

Option	# Ports	Port Diameter	Location
Standard	1	1.9" (48 mm)	Right Side
-TPA	2	1.9" (48 mm)	Right Side
	1	1/4" Swagelok	Right Side
-MPD	6	1.1" (28 mm)	In Door