- Gas Standards Generator

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The AutoBlend is an integrated computer-controlled gas blending system designed to create flowing, adjustable-concentration complex gas mixtures and test atmospheres. The system introduces precisely controlled trace concentration components into a flowing, high purity matrix gas.The AutoBlend uses KIN-TEK Trace Source™ disposable, refillable and diffusion permeation tubes for over 500 chemicals.The AutoBlend has six permeation tube ovens. Each oven can generate its component concentrations independent of the other ovens.  This is an extremely powerful feature for dynamically testing the effects of a wide range of vapor contaminants since each oven can be switched in (span) and out (vent), and the concentrations generated by each spanning oven are independent of the concentrations generated by the other spanning ovens.

The AutoBlend gas standards generator provides:

  • Six independent permeation tube ovens with wide temperature range controlled to 0.1 °C
  • Primary dilution mass flow rate to 10 lpm
  • Secondary dilution mass flow rate to 10 lpm
  • Can create mixtures with up to 48 permeation tube components
  • Dual headspace and humidification options available

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 oven 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 concentrations.

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 above) 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 with the optional humidification module.  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.

Hardware is included to assure constant gas stream output conditions independent of variations in flow and pressure. This is particulary important for applications where flow capacity is limited (e.g., filling of gas bags), or when back pressure is required to introduce the output gas stream sample to the device under test at an elevated pressure. Controls are provided on the front panel for adjusting the output pressure.

Please scroll up and click the 'Software', 'Applications' and 'Specifications' tabs above to see more features and specifications of the AutoBlend.

 

The Windows-hosted AutoBlend software:

  • Manages an inventory of methods, permeation tubes and optional 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.

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 below). 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.

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.

The figure below shows an example method setup in which three permeation ovens (PM-1, PM-4 and PM-6) are to be used. The method consists of 9 points composed of a combination of zero and span functions. Point 2 (highlighted) is a 'span' point with the following configuration:

  • Oven PM-1 has multiple components (not all shown), with a target concentration of 200 ppbv for Methanol.
  • PM-4 has a water tube with target concentration of 30 ppbv and is not used for this point ('use' is unchecked)
  • PM-6 has an H2S tube with target concentration set at 1 ppmv and is on standby (vented).
  • Headspace modules HM-1 and HM-2 are not used in this method
  • Humidification is not checked; thus not used for this point
  • Span run time is set to 20 minutes for this point

The above figure illustrates the AutoBlend's flexibility in generating complex test atmospheres by varying the chemical composition and humidity levels within each point of a method. Experiments can be easily setup to evaluate the effects of various combinations of chemicals on a device under test.

During a method run, the AutoBlend software periodically logs generated concentrations for each point in the method (see Fig. 3) 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.

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 with an RS-232 serial port (or USB-to-RS232 adapter) connected to the AutoBlend instrument. 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.

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