1989-02-01

An Improved Shunt Activated Wiegand Pulser 890478

BASED OK THE RECENT ADVANCEMENTS made in application techniques a new “shunt activated” pulser has been developed using the “Wiegand Effect”. Unlike the more typical moving magnet Wiegand pulsers wherein the pulses are produced in response to the passing of external magnets, a “shunt activated” pulser contains its own magnetic circuit. The internal magnetic fields, to which the Wiegand wire is exposed, are altered by the presence of ferrous objects and thereby cause Wiegand pulses to occur. Although the concept of a Wiegand pulser which is activated by the passage of a ferrous object is not new, development of a balanced bridge magnetic circuit has allowed its evolution into a viable product for industrial or automotive use.
Previous designs, while functional under laboratory conditions, were plagued with difficulties in manufacturing and setup. The new design described in this paper yields an easily manufactured pulser that is magnetically stable and produces symmetric output pulses over its useful air gap range. In the early designs, the extent of the shunting, (the proximity of the shunting element to the pulser surface) had a direct impact on only one phase of the magnetic field to which the Wiegand wire was exposed and subsequently influenced the operating mode of the wire. While some applications capitalized on this phenomenon, more commonly it was a source of problems in situations with excessive shaft runout, rotational eccentricity, etc.
With the newly patented “Balance Bridge” circuit the Wiegand wire is subjected to equal excursions of reversing polarity magnetic field as a shunting element enters and leaves the sensing area. Hence, on a pass by pass basis, a symmetric output can be achieved regardless of the finite value of the shunting provided it achieves an operational minimum flux excursion.
The incorporation of the magnetic circuit into the pulser unit simplifies and reduces the cost of most actuator mechanisms. In many cases existing features such as ferrous gear teeth or shaft keyways may be sensed by these units. This, combined with the inherent advantages of the Wiegand Effect, (near zero speed operation, no power required, and −40° to +200°C temperature capability) make this sensor most attractive for industrial and automotive applications.
Similarly, the “Balanced Bridge” magnetic circuit explained in this paper, may be used to enhance the resolution of other magnetic sensing technologies such as Hall Effect or Magneto-resistive, by producing an extremely sharp “zero crossing” point as the internal field is reversed by the passage of the shunting member. Analog magnetic sensing devices combined with “zero crossing” electronic circuitry may produce highly accurate timing signals at low speeds or with minimal motion.

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