Magnetic proximity sensors are noncontact proximity devices utilize inductance, Hall effect principles, variable reluctance or magneto resistive technology. Magnetic proximity sensors are characterized by the possibility of large switching distances, available from sensors with small dimensions. They detect magnetic objects (usually permanent magnets), which are used to trigger the switching process.  As the magnetic fields are able to pass through many non-magnetic materials, the switching process can also be triggered without the need for direct exposure to the target object. By using magnetic conductors (e.g., iron), the magnetic field can be transmitted over greater distances so that, for example, the signal can be carried away from high temperature areas.  The measurement of proximity, position and displacement of objects is essential in many different applications: valve position, level detection, process control, machine control, security etc. Proximity sensing is the technique of detecting the presence or absence of an object using a critical distance. A position sensor determines an object's coordinates (linear or angular) with respect to a reference, displacement means moving from one position to another for a specified distance (or angle). In effect, a proximity sensor is a threshold version of a position sensor.