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Inductive Position Sensor and Electromagnet

The inductive sensor utilizes the inductance change
• as a result of movement of the ferromagnetic core in the coil
• as a result of the approaching ferromagnetic material
Figure 3.26 Position sensor: (a) The core is moving flat (b) The rotating spinner I core (c) The series of inductance variables

The reader circuit changes the inductance
• two inductors arranged in bridge circuit, one as dummy
• bridge bias voltage is ac signal
• the change of the inductation is converted linearly into a voltage change
K L = sensitivity of inductance to position
• ac output voltage converted to dc or read using phase detector

Figure 3.27 Inductive position sensor test circuit

Electromagnetic sensors use the emf force generated by coils undergoing magnetic field changes
• the output voltage is proportional to the rate of change of the coil position to the magnetic source
• the magnetic field changes obtained by the movement of the magnetic field source or the movement of the coil (as in the microphone and loudspeaker)
Figure 3.28 Position sensor usage: (a) on the microphone, (b) on the loudspeaker