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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 centrepiece 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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Available in three different grades

Since a pulse encoder offers advantages in various applications, our sensors are available in three different grades.
Such sensors can be used in sensitive Systems with higher demands on the pulse.
In our data sheets you will find all information about the different characteristics, whereby the standard sensor fully
meets the requirements for the use as a rotary encoder. The greater pulses of our Sigma-sensor and the reduced
dispersion of the Quantil-sensor offer you additional space for your application.

 

   
   
 

Article in the Polyscope

Wiegand, Impulsdraht, Absolutdrehgeber