Appliance Design - February 2009 - (Page 17)

CONTROLS & SENSORS Standard: Detected Gas(s): Trip Point: Operating Temperature Range: Storage Temperature: Voltage: Humidity: Fig. 2. CSA agency ratings. ANSI Z21.94 / CSA 6.31. gasoline vapor. 50 kOhms. 0 DegC to 65 DegC (32 DegF to 150 DegF). -40 DegC to 80 DegC (-40 DegF to 176 DegF). 5 VDC. 10 percent to 90 percent RH. the emerging FVIR power vent water heater design met the new standard. Specifically, this sensor was studied against four water heater test protocols in a specially designed and CSA-certified Flammable Vapor (FV) test chamber to evaluate product performance under harsh operating conditions dictated by the new standard. Also, along with the water heater OEMs, Therm-O-Disc was an active member of the Gas Appliance Manufacturers Association technical group that worked in conjunction with ANSI and CSA to develop the Flammable Vapor Sensors and Systems standard, ANSI Z21.94/CSA 6.31. The technology This involvement led to the development of the 25VS flammable vapor sensor to detect vapors released during a typical gasoline spill. (See Fig. 1.) The sensor offers long life and good sensitivity to most gasoline components within a wide operating temperature range of 0 DegC to 65DegC. Additionally, the 25VS is certified by the CSA to the aforementioned ANSI standard and meets all requirements developed by the members of the Water Heater Industry Consortium. (See Fig. 2.) The sensor technology is comprised of three primary components: a sensor film, an insert-molded base, and a molded cover. The sensor film is a proprietary mixture of silicone and carbon that is deposited on the insert-molded base and protected by a thermoplastic cover that is ultrasonically welded to the base. The custom-designed silicone system provides a robust foundation and support structure for the carbon. The carbon, which acts as a conductor, is dispersed throughout the silicone such that, in the absence of gasoline vapor, the carbon particles are in solid electrical contact. When the silicone encounters gasoline vapor, it expands, pulling some of the carbon particles apart and increasing the resistance of the sensor. The magnitude of the increase in resistance depends upon the gasoline vapor concentration — higher concentrations cause increased expansion of the silicone film, which results in a higher sensor resistance and vice versa. Design considerations The 25VS flammable vapor sensor yields several unique benefits when compared with other vapor sensing technologies. Unlike active sensors that typically utilize metaloxide or infrared technologies, the 25VS does not require an external pow- er source to detect flammable vapors, only the amount of power used by the application’s control circuit to read the sensor’s resistance. This feature provides design flexibility and contributes to the efficient operation of the water heater control circuit to which it is connected. Also, the 25VS delivers good sensitivity for a broad range of gasoline components, while being relatively insensitive to vapors from most household cleaners. Another benefit is that the 25VS has been designed to provide a long operational life in the application, in some cases up to 15 years depending on operating conditions and other factors. The polymer-based 25VS was designed to accommodate a normal range of ambient conditions. However, the 25VS is moderately sensitive to ambient temperature, as such resistance does increase with temperature, but the water heater manufacturers have been able to accommodate this characteristic in their FVIR system designs. New platform Encouraged by the successful launch of the 25VS, Therm-O-Disc has initiated a technology development program to expand the use of this technology to other appli- Fig .3 .N ext - ge ne rat ion vap or sen sor . www.applianceDESIGN.com applianceDESIGN February 2009 17 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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.