The Echlin Manufacturing Company

John R Wiegand

John E Opie

A Wiegand wire module is excited by a non-uniform field, which may vary in time either symmetrically or asymmetrically, to provide a switch in state of the Wiegand wire thereby inducing a pulse in the pickup coil of the module. The non-uniform field has a maximum value in an axial direction at a center portion of the wire and a minimum value in an axial direction at end portions of the wire. As the amplitude of the field is varied to switch the wire, the end portions of the wire remain in a field having a low axial magnitude. The result is an output pulse substantially greater than obtained through symmetric exitation using a uniform field.

Pulse generator with shaped magnetic field

A pulser unit is composed of two high strength magnets spaced apart from one another and establishing an intense magnetic field therebetween. Forward faces of the two magnets establish a working surface for the pulser unit. A Wiegand wire module consisting of a Wiegand wire segment around which a pickup coil is wound is mounted in the pulser unit immediately behind the working surface of the pulser unit and adjacent the sides of the two spaced apart magnets. The magnetic field is sufficiently strong to determine the state of the Wiegand wire. When a low reluctance element is brought adjacent to the front of the working surface, the field is substantially distorted and the field to which the Wiegand wire is subjected changes materially. The result is that the Wiegand wire switches state and the substantial rate of change of the flux in that switching of state is sensed by the pickup coil to provide an output pulse. Similarly, removal of the low reluctance element causes the field to revert so that the wire switches state back thereby inducing an output pulse in the pickup coil. The pulser can conveniently be kept stationary while the actuating low reluctance element is moved past the working face of the pulser.

Pulse generation by changing magnetic field

A read head for a Wiegand type wire establishes an asymmetric field to which the wire is subjected. A setting magnet at a first position establishes a sufficiently strong positive field to set the core and shell of the Wiegand wire in a first confluent state. At a second position, the field is sufficiently negative so as to assure that the core switches state thereby establishing a reverse state for the wire. The field does not go strongly negative and thus the state of the shell is not reversed. At a third position, the field becomes sufficiently positive so as to cause the core to reverse its state again thereby switching the wire from its reverse state to its confluent state. This particular switching occurs in close proximity to the pickup coil thereby providing an output pulse in response to the switch of state of the wire from reverse state to confluent state.

Pulse generator using read head with Wiegand wire

The magnetic switching device which employs what has come to be known as the Wiegand Effect is described in U.S. Pat. No. 3,820,090. What is disclosed herein is an improved switching device made from an alloy of iron, cobalt and vanadium that provides a greater switching effect. An improved or optimized torsional strain routine for fabricating the wire switching device is also disclosed. The improved switching device provides its maximum output pulse when the wire is switched in an asymmetric fashion.

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Valley Stream, NY, United States of America

John R Wiegand