AUTOBLEND Complex Gas Mixture Generator

AUTOBLEND™ Complex Mixture Generator

OVERVIEW

The AUTOBLEND™ [brochure] is a computer-controlled gas blending system designed to create flowing, adjustable concentration complex gas mixtures and test atmospheres. As a tool for chemical effects and other testing, the system introduces precisely controlled trace concentration components into a flowing, high purity matrix gas. Permeation tubes are used as a controlled source of each trace level component.

The AUTOBLEND™ is a six-channel system in which the component concentrations added by each channel are independently controlled. This feature makes it an extremely powerful tool for dynamically testing the effects of a wide range of vapor contaminants in applications ranging from evaluating sensor system response to inhalation toxicology.

Fig. 1 - AUTOBLEND™ Instrument
(Click here for a larger sideview image; 6 mb size; high quality)
(Click here for a large frontview image; 4 mb size; high quality)

Typical Applications

How it Works

AutoBlend Software

Software Features

TYPICAL APPLICATIONS

Typical applications include:

Sensor systems evaluation
Catalyst research
Inhalation toxicology
Fuel cell development
Analytical methods development

Evaluating Sensor Response
Chemical sensor systems are typically designed to give rapid indication
of the concentration or change of a hazardous substance in a normally
safe background. Often, however, many innocuous and possibly interfering compounds are also routinely or transiently present. For example, DEET-based mosquito repellant commonly used in an outdoor location might result in false positive toxic gas alarms. Or the presence of a safe compound might suppress response to a hazardous compound.
Often, sensors either respond to atmospheric humidity, or their response is affected by humidity. Identifying and quantifying such interactions is critical to qualifying a sensor system for use in a specific application.

Catalyst Research
In catalyst research and development it is important to define and quantify the effects of reactant impurities and combinations of impurities on yield and catalyst life. The AUTOBLEND™ system’s ability to vary relative concentrations of the components can dramatically reduce testing time. It facilitates discovery of synergistic effects and is ideal for executing statistically designed vapor testing programs.

Inhalation Toxicology
The AUTOBLEND™, with its capability to give varying ratios between components, coupled with its integral variable humidity source and the adjustable headspace vapor modules, is an extremely versatile source of test atmosphere for inhalation toxicology studies. The system is simple to set up for a wide range compounds. It can give concentrations from hundreds of ppm down to low ppb, and mix them into humidified air also containing various common and normally innocuous atmospheric contaminants.

Fuel Cell Development
Fuel cells offer an opportunity for direct, or near direct conversion of chemical compounds to electrical energy with minimal environmental pollution. Success of these efforts requires development of robust catalytic systems, and thus an intimate knowledge of the long-term effects of various fuel and air (or other oxidant) contaminants. The AUTOBLEND™ system is an excellent source for long term testing of fuel cell systems known concentration conditions.

Validating Analytical Methods
Effective analytical methods must work equally well in any laboratory setting and with a wide range of variation of reagent and/or matrix composition. The flexibility of the AUTOBLEND™ system allows for rapid and thorough evaluation analytical methods. A clear understanding of the method and significant parameters is essential to establishing standard methods.

HOW IT WORKS

The system features six independently-controlled permeation ovens. The base gas mixture created in each oven can contain up to eight different analyte components so that a test atmosphere can be spiked with up to 48 components simultaneously.

A small flow of pure dilution gas passes over the permeation (or diffusion) tubes installed in each channel to form a base gas mixture. A variable portion of each base gas mixture is then added to a main dilution flow to create a primary mixture with variable concentration ratios.

A secondary dilution feature provides a large dynamic concentration range. Secondary dilution is used or bypassed automatically in the system as required to produce target concentration levels.

In many applications normally innocuous contaminants that occur routinely, or randomly, may be significant for testing purposes. In the AUTOBLEND™, two optional dynamic headspace saturation modules can be added (as shown in bottom cabinet) to allow the addition of vapors from potential transient interfering compounds such as cleaning solutions, fuels or paints. Output from the headspace modules can be added either before or after secondary dilution of the trace components.

The resulting test atmosphere can be supplied either dry or at variable humidity levels. Humidity is added by splitting the total dilution flow into two parts. One part remains dry and contains all of the trace components from the permeation tubes and headspace modules. The other portion of the dilution gas is saturated with water vapor. The two portions are combined at the output of the system to form the humidified mixture. Relative humidity (RH) is varied by varying the ratio of humidified diluent to dry diluent. The trace components do not contact liquid water in the system.

AUTOBLEND™ SOFTWARE

Designed for use with the AUTOBLEND™ instrument, the Microsoft® Windows® 2000/XP-based AUTOBLEND™ software:

Manages an inventory of methods, permeation tubes and headspace mixtures.
Analyzes the feasibility of creating a specified mixture.
Calculates the setpoint data required to adjust the system to achieve the mixture.
Dynamically maintains the mixture under changing conditions.
Logs operating data and test mixture results.

Fig. 2 - Virtual Instrument of the AutoBlend™ System
(click here for a larger image)

SOFTWARE FEATURES

Permeation Tube and Headspace Inventory Management
The AUTOBLEND™ software contains a database of the user's permeation tube and optional headspace inventory including tube ID and serial number, compound name, emission rate data, temperature alarm criteria, and expiration date (see Fig 3). As the expiration date approaches, the tube is highlighted to warn the user to reorder or recertify.

The following figure shows an example inventory of permeation tubes.

Fig. 3 - Permeation Tube Inventory
(click here for a larger image)

Method Inventory Management
As specific complex gas mixture sets are defined, the details of the components (permeation tubes and headspaces) and required concentrations of up to 20 span points are saved as a method. These methods are saved in an inventory for easy recall and duplication of the mixture at a later date.

Data Logging
During a method run, the AUTOBLEND™ software periodically logs generated concentrations for each point in the method (see Fig. 4) and logs measured values of all operating parameters. Should an unexpected test result occur, the historical data can be checked to verify the mixture and operating conditions such as oven temperature, flow rates, pressures and so forth.

Fig. 4 - Data Log
(click here for a larger image)

Scenario Analysis
The AUTOBLEND™ software set includes a "Scenario Analyzer" CD that allows the user to establish offline the feasibility of achieving a desired mixture. Given desired concentrations, the AUTOBLEND™ software tests the possibility of creating the mixture from specific permeation tubes and headspaces under specific operating conditions. This feedback is invaluable in creating a workable method and can be a major time saver.

System Monitoring
AUTOBLEND™ system functions are monitored in the software and out-of-specification values are reported. For example, the software warns of "over temperature" conditions in the permeation ovens, impossible flow settings, out of range temperature setpoints (for the installed permeation tubes), etc.

Enhanced Functionality
The actual permeation rate from each tube varies with temperature. The AUTOBLEND™ software can correct to actual or estimated temperature depending on supporting data available for the tube. When multi-point certification data is available, the correction is exact at the temperature of the defined certification point, and estimated with a linear or log-linear algorithm when at an uncertified temperature point. Even for a single-point certification, an enhanced estimation algorithm is applied for the case in which the user elects to use a temperature other than the certification temperature.

System Requirements
The AUTOBLEND™ software runs on Microsoft® Windows®2000 or XP with an RS-232 serial port (or USB-to-RS232 adapter) connected to the AUTOBLEND™ Complex Gas Mixture Generator. The AUTOBLEND™ Inventory and data logs are stored in a Microsoft® Access database (Microsoft® Access is not required to be installed). The software requires about 15 MB of hard disk space plus extra storage space for the database.