Inductive sensor

Basic principle of inductive sensors, the control of the inductor by a physical quantity.

The inductance of a coil, for example, depends on the square of the winding number, and the magnetic resistance of the circuit.

• L - inductance
• Rm - resistance of the magnetic circuit
• N - Number of threads

The magnetic resistance of a coil surrounded by the iron is dependent on the field line length (l ) of the penetrated area (A) and the magnetic field, and the permeability constants:

• μ0 - field constant 1.257 · 10-6 Vs / Am
• ĩr - permeability

Operation

Inductive sensors work, as its name suggests, according to the law of induction. This is basically a coil ( winding ), a magnetic field, and " move" necessary. By this measurement principle can be non-contact and thus wear-free angle, paths and velocities measured.

The sensor transmits using a resonant circuit (consisting of a coil and a capacitor ), an electromagnetic field that induces eddy currents in a guided past, electrically conductive material. The amplitude of the resonant circuit is changing. With a Schmitt trigger, the output is switched with a particular change.

The measurement accuracy of the sensor can be increased if multiple coils are used.

Another method uses a solenoid plunger, that is, a movable iron core which is immersed in a coil. The immersion depth of the armature within the coil, the magnetic resistance changes of the same and thus in a further result, the inductance of the sensor.