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Position sensing is one of the crucial parts of many systems, specifically in an active magnetic bearing. The position is used to control the magnetic forces within an active magnetic bearing to keep a rotor levitated. Sensors used in these systems must be very sensitive and are usually very expensive. In this paper a low cost printed circuit board position sensor is analysed. The sensor uses an excitation coil to establish a magnetic field. Four sensing coils are then used to measure the influence a conducting target has on the magnetic field to enable position sensing. The sensor's magnetic operation is analysed using finite element methods and very good correlation is found with measured results. The effects of the target material and the number of PCB layers are analysed. It is shown that a two layer sensor can produce acceptable sensitivity and linearity.

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Abstr-acl: /'I dcsign pnl(;css comprising aspccts of modelling and analysis is dcvcloped, impkmenled and vcrificd for a Ikxihk rotor activc magnctic hcaring systcm. The system is specified to experience the first three critical frequencies up to an operating specd of 10.000 rpm. Rotor stahility at critical frequencics places specil'ic constr,linlS on the equivaknt stillncss and damping p,lrameters of thc active magnctic hcaring. /'In iterative design proccss is Ihen initiated hy an eleetromagnctic design of the r,ldial activc magnetic bearings resulting in paramcters used in the detailed modelling of the systcm. Stiffness and damping parameters as well as system dynamic response arc verified and used to design a Ikxible rotor. The magnctic hearing locations. displacemcnt sensor locations and rotordynamic response arc verified using finite elemel1l analysis. The design of the rotor stands central to thc iterative dcsign process since it impacts on the forces experienccd by the active magnetic hearings as well as thc critical frequencics of the active magnctic bearing system. Once constructed the actual activc magnetic bearing system stillness and damping parameters as well as dynamic rcsponsc arc compared to modelled results. Thc rolOrdynamic response is characterised by measuring thc rotor displacemcnt at pre-dcfincd locations as the rotor traverses the critical frcqucncies. Thesc results arc compared with the predicted rotordynamic responsc.