The inductive measurement procedure is based on the change of the behavior (inductance) of a coil caused by the change in position of a magnetizable material (e.g. soft iron, ferrite), referred to as the core, inside the coil. The change in position of the core fastened to the movable object to be measured by means of a non-magnetizable rod (core rod; core and core rod make up the immersion core) within the coil, which is excited with an AC voltage, is converted into a position-proportional signal by a connected conditioning electronic component.
Carrier frequency measuring amplifier operation
This process is referred to as the carrier frequency process, the electronic component is correspondingly referred to as a carrier frequency measuring amplifier. The carrier frequency measuring amplifier can be integrated into the displacement sensor (so-called DC/DC displacement sensor), or it can be mounted in a separate housing.
Inductive displacement sensor operation
Varying methods of switching the coil(s) (each with pros and cons) can be used for this process:
- configuration of electrically separated primary and secondary coils (differential transformer or LVDT)
- coils with a center pickup (differential inductor or LVIT)
A variant of the method is used in our long-stroke sensor type WP. In this case, an (excited) coil is surrounded by a position-changing tube made of electrically conductive material (aluminum), on the surface of which eddy currents are generated. These draw energy from the coil which is proportional to the percentage of coverage of the coil by the tube and thus can be measured in the connected electronic component (again, a carrier frequency measuring amplifier) and converted to a position signal.
Inductive proximity sensor operation
Eddy current sensors (also known as inductive proximity sensors) use the physical effect of the quality change of a resonance oscillation circuit from which energy is drawn by means of eddy current losses in conductive materials.