The Principle of Operation of an Induction Potentiometer

An induction potentiometer is a rotary type linear-variable inductor with two concentrated windings wound on the stator and on the rotor as illustrated in the figure below:

The rotor windings are excited with an AC, inducing voltage in the stator windings. The amplitude of the output is dependent on mutual inductance between the two coils, where the mutual inductance itself is dependent on the relative positions of the coils, as determined by the angle of rotation. For concentrated coil type induction potentiometers, the variation of the amplitude is sinusoidal, but linearity is restricted in the region of the null position. There are different types of induction potentiometers with distributed coils that give linear voltages over an angle of 180° of rotation.

The standard commercial induction potentiometers function in a 50 Hz to 400 Hz frequency range. They are typically in small sizes from 1 cm to 6 cm, and their sensitivity can be on the order of 1 V/degree rotation. Even though, the ranges of induction potentiometers are limited to less than 60° of rotation, it is possible to measure displacements in angles from 0° to full rotation by suitable arrangement of a number of induction potentiometers.

It is important to note that, the output of an induction potentiometer may require phase-sensitive demodulators and appropriate filters. In a number of cases, additionally dummy coils are employed to enhance linearity and accuracy.

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