HANDOUTECT 0323SENSORS AND TRANDUCER 28 –92 Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved. Chapter 4 Magnetic Field Sensor Magnetic Field Sensor Introduction to Magnetic Field Sensor Magnetic field sensors react to magnetic fields of permanent or electromagnets. Functional Principles Different principles are implemented in the constructions of these sensors. These include Hall sensors, magneto-resistive sensors and saturation core probes. In Hall sensors and magneto-resistive sensors, the lateral deflection of an electron flow through a magnetic field (Hall Effect) is evaluated. Because of the implemented semiconductor materials (effect of temperature), these two methods are less suitable for use as proximity switches. Saturation core probes on the other hand have a more stable operating behavior on account of their low eddy-current and hysteresis losses. Hall Sensor In Hall sensors, the lateral deflection of the electron flow through the magnetic field is evaluated as Hall voltage UH. The Lorentz force is responsible for the fact that the electrons are deflected by the magnetic field. One side is then lacking in electrons whilst the other side is enriched with electrodes. This produces the Hall voltage.
HANDOUTECT 0323SENSORS AND TRANDUCER 29 –92 Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved. Magneto-resistive Magneto-resistive sensors are based on the change in electrical resistance of soft magnetic alloys under the influence of a longitudinal or transversal magnetic field. This relative change in resistance may reach values of several percent in such sensors (material-dependent and at normal room temperature). The magneto resistive sensors which became well-known as field plates are semiconductor elements in which fine needles (e. g. Fe or NiSb) are embedded in parallel. The path through the sensor element is prolonged dependent on the magnetic field which causes an increase in the resistance. Magneto resistive sensors are used increasingly for measuring DC and AC magnetic fields. They are more sensitive than Hall sensors and can be used over a greater temperature range. Principle of Magneto-resistive
HANDOUTECT 0323SENSORS AND TRANDUCER 30 –92 Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved. Saturation Core Probe Saturation core probes are used mainly to determine small field strengths. They exploit the non-linearity of magnetization curves of high-permeable, soft magnetic materials. The probe consists of one or two highly permeable core rods or a toroidal core. Saturation core probe with one core The core material is controlled periodically into saturation by an alternating current in the magnetization winding. This induces a voltage in the probe winding. An alternative method for saturation core probes is the method with a ferrite core and yoke. In this type of probe a resonance circuit is used as in the inductive sensor. The
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- Fall '13
- Magnetic Field, Capacitive Displacement Sensor, Proximity sensor, German Malaysian Institute