Effects of Length and Position Relative to the Rotor of the Magnetostrictive Amorphous Wire in Motor Speed Sensing

Abstract

The performance of the magnetostrictive amorphous wire in motor speed sensing has been shown to match that of conventional motor speed sensors. The sensor is based on Large Barkhausen Jump; sudden reversal of magnetization at a single value of magnetic field, a unique feature of the wire. Large Barkhausen Jump occurs at a given critical length of the wire which also depends on the diameter of the wire. A permanent magnet is also used in speed sensing and therefore, depending on the strength of the magnet used, the position of the sensor relative to the rotor is expected to influence the results hence the performance of the sensor. This paper presents a practical analysis of the effects of length and position of the magnetostrictive amorphous wire on the performance of the sensor. A close observation on the signal waveforms indicates that there is a critical length and optimal position of the wire from the magnet for which the performance of the sensor is satisfactory.