Chapter 6 - Proximity-Sensing Techniques

Abstract

This chapter discusses some of the ways in which permanent magnets and Hall-effect sensors are used to detect the proximity and measure the position of objects. Sensing an object's presence or position are the two most widespread applications in which the Hall-effect sensors are used. Magnetic field sensors are used for this kind of application for two reasons. First, magnetic fields are not significantly affected by nonmagnetic materials and pass through them unhindered and second, the strong magnetic fields do not occur in nature. One of the methods used for the activation of the Hall sensors in binary proximity detection applications is the head-on actuation. In a head-on application, the sensitive axis of the sensor and the axis of magnetization are colinear. The magnetic flux density that the Hall-effect sensor sees after being approached by a magnet pole is highly nonlinear with respect to the magnet sensor airgap. It decreases rapidly as the airgap increases. Another way of using a Hall-effect sensor as a proximity detector is by sliding of the pole-face of a magnet past the device.