Appliance Design - July 2008 - (Page 24)

GAS TECHNOLOGY gas appliance applications. Some newer hot-surface ignition elements have faster heat-up times, but these typically do not have the large thermal mass inherent to the traditional hot-surface elements. In terms of physical design, a hot-surface ignition element is usually a standard, off-theshelf component, requiring the designer to design the burner system around the standard element geometry. Furthermore, because a hot-surface element is comprised of ceramic materials, the thermal cycling inherent to ignition systems will cause a change in physical and operating characteristics. This includes the possibility that the element will not achieve adequate ignition temperature over time. Thermal cycling also causes the ceramic element to become more brittle, increasing the potential for breakage and failure, often before the ANSI Z21.20* life requirement of 100,000 cycles for household appliances incorporating a safety control. Additionally, the hot-surface element does not tolerate contamination very well, forcing the designer to fashion elaborate shielding schemes to protect the element. Water and dirt negatively affect the system and can cause failure catastrophically – the element can shatter. The third, and newest, gas ignition technology can address some of the concerns with the other two and can provide an optimal technical solution for many gas burner ignition applications. This hot-wire ignition system utilizes a small coil of resistive wire that operates off 3 V and usually achieves ignition temperature within three seconds. The hot-wire coil is not ceramic, but a coil of extremely durable metallic resistive wire that is welded between two electrodes. The key distinction of the system is its ability to provide an adequate thermal mass to achieve ignition, while optimizing design flexibility for a variety of applications. The hot wire is coiled to a diameter of about 1/8 in. and to a length of about 1/4 in., with wire gauge determined by the application. This geometry is uniform throughout all applications, as ignition is a function of location relative to the burner. When energized, the coil achieves more than 2,000 DegF and is suitable for either natural gas or propane systems. The wire used in the coil is not the common nickel-chrome, which is often used in toasters, nor is it any similar material that can become brittle. Instead, the wire is made from a unique, proprietary metallurgical alloy that is designed to be in the flame of the burner (where required by the application) and will maintain its ductile properties throughout its life. The hot-wire coil is CSA certified to 100,000 cycles and passes the ANSI Z21.20 ignition system requirement. Hot-wire design versatility is similar to that of spark electrodes in that it can be retrofitted to existing platforms with little burner system redesign. Unlike spark ignition, however, the low-voltage characteristics of the hot-wire system eliminate concerns about radiated EMI, or a highvoltage spark not finding the correct point of ignition. In addition, designers need not worry about finding a high-voltage/hightemperature wire that will degrade over Customers everywhere depend on our igniters. No matter where you are, from the North Pole to the South Seas, Saint-Gobain has an igniter to meet your needs. Our igniters deliver dependable performance in gas appliances of every description, from furnaces and boilers to ranges, cooktops, and dryers. Made with a state-of-the-art ceramic, our igniters offer physical and thermal strength, electrical stability, easy handling, and simple installation. They are available in virtually every voltage, including 12V, 24V, 120V, and 240V. Slotless MINI-IGNITER™ CRYSTAR® Igniter For more information about Saint-Gobain Igniter Products – makers of the original Norton Igniter – call us at 603-673-2681 or visit us at www.igniterproducts.saint-gobain.com. After all, when it comes to reliability, our igniters beat the others cold. AD12074StGobain.indd 24 applianceDESIGN 1 July 2008 11/16/07 9:17:17 AM www.applianceDESIGN.com http://www.igniterproducts.saint-gobain.com http://www.igniterproducts.saint-gobain.com http://www.appliancedesign.com

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Appliance Design - July 2008

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