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Magnetic switch puts electrons in the spin cycle

Bruce Wiebusch, Midwest Regional Editor -- Design News, May 7, 2001

Chicago—Bimba Mfg. Co. introduced giant magneto-resistance (GMR) sensing technology at the National Design Engineering Show here in March. With repeatability of 0.002 inch, it is said to be more sensitive to magnetic fields than Hall-Effect sensors (which have repeatability of 0.015 inch) in automotive, computer, and other applications.

The GMR technology is based on a discovery that the direction of electron spin in certain metals can be shifted in the presence of a magnetic field. A GMR sensor is made from multiple layers of a nickel/iron compound, with each layer magnetically opposed to the adjacent one.

Current flowing through this material usually encounters resistance. But when a magnetic field is applied, the layers become magnetically aligned. This alignment reduces the resistance of the material, allowing for greater current flow through it.

The resistance change produces a voltage potential in a resistor network, which is amplified and sent through a comparator, which in turn causes the device to switch to a preset threshold. This switching output is buffered through an output transistor. The switch is resistant to over-voltage, reverse-polarity, and electrical transients. All of Bimba's GMR switches include a minimum of 500 watts transient protection.

For more information about switches from Bimba: Enter 533

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