SENSORS

MAGNETIC / HALLWhat is a magnetic sensor?Magnetic sensors detect the presence or strength of amagnetic field. A simple magnetic sensor is a reed switch,which has flexible contacts made of iron-bearing magneticmaterials that make contact when a strong enough magnetexerts a force (magnetism) on them. Magnetic sensors usevarious sensing techniques like Hall effect or magnetoresistivefor various applications.Recently the MEMS magnetometer, which measures themagnetic field strength or direction, became popular as it canacquire accurate orientation-independent compass headinginformation when used in conjunction with a three axisaccelerometer.ApplicationCasesPosition, speed orcurrent sensingMotor controlMagnetic patternrecognitionReal Life ExamplesNeedle position in industrialknitting machinesRotary switches (human machineinterface)AC/DC motor position controlsRoboticsBrushless motorsVibration motor driversFan/motor driversATMs, cash counters, billchangers, ticket machines,automatic vending machines,card readersImportant selection parametersMagnetic Field Range defines the range of magnetic fieldstrength that a sensor can measure.Operating Point defines the threshold level of magnetic fieldthat causes the sensor output to turn ‘on’.Release Point defines the threshold level of magnetic fieldthat causes the sensor output to turn ‘off’.Sensitivity, for a linear or proportional magnetic sensor,defines the transfer function (ratio) of the output change, inproportion to the applied magnetic field.Typical applicationsThere are a multitude of magnetic sensor types adaptedfor different applications – Hall sensors are often used forposition/speed detection (linear or rotating) when used witha magnet and/or magnetic toothed object. Magnetic sensorsare well suited for use in harsh environments and have longlife since they are sealed and have no contacts to wear out.Other types are specialized for motor control applicationsand include motor drive electronics as well. Anotheruse is in magnetic compasses, using the most sensitivedevices to detect the earth’s natural magnetic field. Sinceelectric conductors produce a magnetic field proportionalto the current they carry, other devices can be used tounobtrusively measure current or power in this way. Recently,highly accurate and inexpensive 360-degree magneticrotational position sensor ICs have become popular formotion control & robotics and feature several output types,both analog and digital.MAGNETIC / HALL47www.FutureElectronics.com/Sensors