Appliance Design - February 2009 - (Page 16)

CONTROLS & SENSORS VAPOR Fig. 1. The 25VS flammable vapor sensor. SENSING Safety technology updated for broader use. R by eric boggs and jeffrey west Eric Boggs is project manager and Jeffrey West is new product development manager, Polymer Sensors, Therm-O-Disc, Subsidiary of Emerson, Mansfield, Ohio. 16 applianceDESIGN February 2009 esidential gas water heaters have long been considered safe when properly used. Yet the potential dangers resulting from the improper use and storage of gasoline and other flammable materials in the vicinity of the water heater have continued to be a concern among manufacturers of residential gas water heaters. Due to the unique operation cycle of the power-vent water heater in which the blower is activated for up to 60 seconds at the beginning of every heating cycle as a system purge, flammable vapors may be drawn inside the water heater prior to ignition of the burner. In 1995, the Water Heater Industry Joint Research and Development Consortium (WHIJRDC) was formed to determine whether a residential gas water heater could be made more resistant to accidents caused by mishandling or improper storage of gasoline or other flammable materials. As a result, new Flammable Vapor Ignition Resistance (FVIR) requirements were developed, and the existing American National Standards Institute (ANSI) gas water heater standard was revised. By July 2006, all powervent water heaters produced in the U.S. and Canada were required to comply with the new FVIR standard. Given the potential for flammable vapor ignition inside the water heater, the Consortium recognized a need for a technology solution that senses the presence of flammable vapors and prevents the blower purge cycle from starting, thereby preventing the operation of the gas valve and ignition of the burner. A new standard Emerson’s Therm-O-Disc business unit, a manufacturer of sensors, controls and electrical switches, was asked by the Consortium for a proposal to address this new flammable vapor sensing need and the company became a key contributor to the development of a flammable vapor sensor for the water heater OEMs’ power vent FVIR system. Therm-O-Disc took on the challenge of developing a sensor that would detect the presence of a specific concentration of flammable vapors in less than a minute after a spill, and then would enable the control module to prevent the supply of gas and burner ignition — thereby preventing the ignition of vapors both inside and outside the water heater. Over several years, Therm-O-Disc engineers worked to ensure that the sensor in www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - February 2009

Appliance Design - February 2009 Contents Editorial Shipments/Forecasts News Watch Force-Sensing Technology Offers Designers an Alternative Approach to Creating Touch-Control Interfaces A Flammable Vapor Sensing Technology that was Originally Developed for use in Water Heaters has Evolved for use in a Broader Array of Applications Latches, Hinges, and Slides Must Reliably Secure Parts Together, Sometimes for Hundreds of Thousands of Cycles. Beyond their Utilitarian Functions, They Can Also Change Consumer Perceptions Elastomeric Electrical Connectors Can Solve Space Constraint Problems in Electronic Products and Provide Some Cost Advantages as Well A Multi-Layer Ceramic Capacitor with a Novel Electrode Design Can Suppress Electromagnetic Interference, Improve Circuit Performance, and Reduce the Number of Needed Components Design Marts Association Report: AHRI Advertisers’ Index

Appliance Design - February 2009

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