Optical Reflectance Sensor Measures Displacement in Magnetic Suspension

In active magnetic suspension systems, electromagnetic forces are used to keep a body in stable equilibrium without mechanical contact. Basically, an active magnetic suspension is a position servomechanism. Thus, accurate measurement of the position of the levitated part is important. A variety of displacement transducers has been in use, the eddycurrent sensor being the most favored one at present. This paper describes an optical reflectance sensor used in a novel configuration to measure the position in a levitation setup. A sensitivity of 10.5 V/mm, and a linearity range of about 0.5 mm, were obtained by this method. The sensor and the measurement technique are described in detail here.