Appliance Design - August 2007 - (Page 14)

SWITCHES & RELAYS Reliable Reeds A benefit of reed relays are their tiny size. Photo by Meder. Simple devices have a myriad of uses. by larry adams 14 applianceDESIGN August 2007 here is elegance in simplicity, and few things are as elegantly simple as a reed switch. The technology is basic and time-tested, and has not changed much in the seven decades it’s been around. But, because of their versatility, product designers are continually finding new uses for the tiny devices. And that’s one reason why these millimeter-sized devices are sold by the hundreds of millions each year. Two other important reasons: reed switches have extremely long life compared to other electromechanical switching technologies and they don’t corrode, despite often being asked to go into harsh environments. A reed switch is a basic switching device that is actuated by a magnet. The switch is made from two slim, ferromagnetic blades — the reeds. The reed ends are plated with a thin layer of precious metals that ensure a good electrical contact. The switches are encapsulated in a hermetically sealed glass enclosure with an inert gas, typically nitrogen, which will minimize the possibility of electrical arcing. In its simplest, two-reed form, actuation occurs when a magnet passes near the reed and the two blades are drawn to each other to make electrical contact. When the magnet T passes the reeds, the reeds spring back to their original position and the contact is broken. Additional versions are available depending on the requirements of the application. Tworeed versions, which typically have normally open (NO) contacts, are also available with normally closed (NC) contacts. In this case, the reeds are held together by a permanent magnet in their normal state, and another magnet with opposite polarity is needed to actuate it. There are even three-reed versions that have a pair of normally open and normally closed contacts. Reed switches can be as small as a couple millimeters long and they typically can handle only a couple of amps, but this, too, may be changing. Reed Switch Developments Corp., Racine, Wis., a company that develops reed switch applications employing multiple vendors is using what it calls the one of the largest capacity reed switches in the world on projects for two of its customers. The reed switch, made by Japan-based Yaskawa, operates at 240 VAC, 10 A Maximum. While reed switches do not have the sophistication of solid-state switches and relays such as a Hall Effect relay, the simplicity of a reed switch remains its key strength, says Simon Pitkin, the UK-based sales and www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - August 2007

Contents Editorial Shipments/Forecasts News Watch A Reed Switch is Simople, yet Versatile, and Designers are Finding New Uses for this Time-Tested Technology A Novel Actuation and Sensing Technology can Register a Light Touch, but Resist Blows from a Hammer Tracing the Source of Noise is Made Easier with Noise Source Identification Methods Appliance Noise can be Annoying, but Designers have Many Material Choices to Help Rein in the Racket Nanocomposites are No Longer a Technology for the Future. These Plastic Materials are Already on the Job A New High-Strength, Low-Density Glass-Microsphere Additive can Improve Plastic Part and Molding Performance A New Electromagnetic Weld/Bonding Process Helps Ensure Long-Term Integrity of Joints in Plastic Parts Snap-Based Technology Eases Installation and Makes Products More Serviceable Two-Part Silicone Adhesives Provide a Rapid-Cure Alternative to Traditional One-Part Silicones Classified DesignMart Advertiser’s Index Association Report: GAMA

Appliance Design - August 2007

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