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Definition: Wiegand wire

An iron-alloy wire that has unique magnetic properties. Invented by John Wiegand in 1972 and used in sensor applications, the Wiegand wire's outer layer can be magnetized without affecting the inner core. When an external magnetic field is applied, the core switches polarity to that direction and emits a large pulse. As the field is intensified, a smaller pulse is emitted.

Magnetic Key Codes
Used in keycard door locks, the plastic keycards have two embedded rows of Wiegand wires in a specific polarity pattern that represents a 26-bit ID number. When run through a magnetic field strong enough to switch the polarities of the inner cores, pulses are generated. The pulses energize a coil that creates a signal detected by a sensor. Although Wiegand cards are not as predominant as they were in the past, the 26-bit ID format has been carried over to many access control systems. See access control.