Wiegand sensor production
The Impulse Wire Sensor, that is not protected by any patent, also known as the Wiegand Sensor can be used in any application, where revolutions shall be counted, position determined, or movement detected. The centerpiece of the rotary or position encoders with Wiegand-technology is the electromagnetic Wiegand sensor comprising of two essential components: a piece of Wiegand wire and a copper wire coil with ferrite beads.
The Wiegand wire named after John R. Wiegand is an approximately 0.25 mm diameter wire made of Co‑Fe‑V alloy (Vicalloy).
By a special mechanical and thermal conditioning is it possible to produce a wire with a magnetically hard mantle as an outer layer and a soft magnetic core whereby the mantle acts as a permanent magnet with north and south pole at the wire ends due to the axial alignment and fusion of the so-called Weiss domain.
The physics of a Wiegand wire
When the Wiegand wire is exposed to a sinusoidal magnetic field, the core aims to align its field accordingly but the magnetostrictive forces in the mantle at first prevent this process. Finally, these forces get conquered with aid of the magnetically biased mantle as the external magnetic field increases. This leads to an abrupt reversion of magnetic polarity of the core and to a new steady state of the Wiegand wire
This so-called Barkhausen jump always takes place at the same speed independently from the increasing speed of the external magnetic field.
When the Wiegand wire is placed in the center of a copper coil, the abrupt polarity reversion of the core creates a voltage impulse. The ferrite beads at the end of the copper coil allow a better alignment of the external magnetic field that increases the magnetic bias of the mantle and thus increases the impulse voltage.
Rotary encoders with Wiegand-Technology
The Wiegand-sensor generates one positive and one negative voltage impulse due to two Barkhausen jumps per revolution when the external magnetic field is generated by a rotating, diametrically polarized permanent magnet. The patented application as a rotary encoder combines an energetically optimized Wiegand sensor with an ASIC module that does not only counts the voltage impulses thus revolutions but also uses these impulses as its own power supply by charging a capacitor via a rectifier. A such rotary encoder can work without any external power source. Moreover, a special procedure patented as well determines the rotational direction with one sensor only.
A technical challenge
Every single Wiegand sensor produced by Werap must generate voltage impulses with enough energy in order to guarantee an all-time reliable counting with the absolute, self-sustaining rotary encoder. Since the Wiegand wire characteristics considered over length can be very inhomogeneous due to the mechanical and thermal treatment, every single approx. 10mm long piece of wire must be qualified and assorted by cutting it out using a testing device specifically developed for this purpose.
Another challenge is the cutting process itself. It must be performed very gently since it implicates a mechanical stress that can weaken or defeat the Barkhausen jump resulting is decreased or eliminated voltage pulses.
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