Motion transducers that employ the principle of electromagnetic induction are termed variable-inductance transducers. When the flux linkage (defined as magnetic flux density times the number of turns in the conductor) through an electrical conductor changes, a voltage is induced in the conductor.
This, in turn, generates a magnetic field, which opposes the primary field. Hence, a mechanical force is necessary to sustain the change of flux linkage.
If the change in flux linkage is brought about by a relative motion, the associated mechanical energy is directly converted (induced) into electrical energy this is the basis of electromagnetic induction, and it is the principle of operation of electrical generators and variable-inductance transducers.
Note that in these devices, the change of flux linkage is caused by a mechanical motion, and mechanical-to-electrical energy transfer takes place under near-ideal conditions.
The induced voltage or change in inductance may be used as a measure of the motion. Variable-inductance transducers are generally electromechanical devices coupled by a magnetic field.
There are many different types of variable-inductance transducers. Three primary types can be identified:
1. Mutual-induction transducers
2. Self-induction transducers
3. Permanent-magnet transducers
Those variable-inductance transducers that use a nonmagnetized ferromagnetic medium to alter the reluctance (magnetic resistance) of the flux path are known as variable-reluctance transducers.
Some of the mutual induction transducers and most of the self-induction transducers are of this type.
Permanent-magnet transducers are not considered variablereluctance transducers.