How to select a magnetic switch technology

Because no magnetic switch technology best fits every application, Hermetic Switch Inc. and technology consulting firm TekMark Growth Partners analyzed four magnetic switch technologies.

Reed (electromechanical) switches do not consume power in the off mode, have hermetically sealed contacts, and are highly resistant to electrostatic discharge (ESD). These devices provide switching and sensing functions in one package, saving on cost and labor. Reed switches can be established technology with proven reliability. Limits: Capital cost of reed switches may be more per unit than other magnetic switches, but quality, performance, and reliability can reduce overall cost. Reed switches have been larger in size than other magnetic switches.

MEMS (microelectromechanical) switches’ strengths include a small footprint (as small as 0.110 in. long) and high magnetic sensitivity, as low as 1.7 mT. They can withstand physical shock to 15,000 G and are relatively inexpensive, making them a good choice for high-volume, low-cost commercial applications. Limits: They are ESD sensitive. Switch contacts are not hermetically sealed so electrical contacts can become contaminated, causing sticking or other malfunctions. MEMS switches generally have higher contact resistance than other magnetic switch technologies.

Hall-effect (solid-state) switches are inexpensive and suited for high volume, low-cost commercial applications. They have very long life expectancy. When operated within electrical specifications, Hall switches can operate for billions of cycles. These switches have no contact bounce. They are also durable and resistant to shock and vibration. Limits: They require power even when “off.” Hall-effect switches cannot switch loads. They have a low signal output, usually requiring amplification circuitry. Hall-effect switches also are ESD sensitive.

GMR (giant magnetoresisitive) switches are solid-state devices, have a small footprint (some as small as 0.04 in. or 1.0 mm sq), and very magnetically sensitive. Some have magnetic sensitivity as low as 1.0 mT and can maintain a very tight operating point. This switch family operates in a wide temperature range, -40 to 150 °C. Limits: GMR switches require constant power and are ESD sensitive. They are based on a relatively new, evolving technology.

www.hermeticswitch.com , www.tekmarkgp.com

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