Purpose and Working Principle of Inductive Sensors
Purpose and Working Principle of Inductive Sensors (on photo: Omron 5mm 6-36VDC inductive proximity sensor switch PNP NC)

Inductive sensors use currents induced by magnetic fields to detect nearby metal objects. The inductive sensor uses a coil (an inductor) to generate a high frequency magnetic field as shown in Figure 1 below. If there is a metal object near the changing magnetic field, current will flow in the object.

This resulting current flow sets up a new magnetic field that opposes the original magnetic field. The net effect is that it changes the inductance of the coil in the inductive sensor.

By measuring the inductance the sensor can determine when a metal have been brought nearby.

These sensors will detect any metals, when detecting multiple types of metal multiple sensors are often used.

Inductive Proximity Sensor
Figure 1 – Inductive Proximity Sensor

Note: these work by setting up a high frequency field. If a target nears the field will induce eddy currents. These currents consume power because of resistance, so energy is in the field is lost, and the signal amplitude decreases. The detector examines filed magnitude to determine when it has decreased enough to switch.

The sensors can detect objects a few centimeters away from the end. But, the direction to the object can be arbitrary as shown in Figure 2 below.

Shielded and Unshielded Sensors
Figure 2 – Shielded and Unshielded Sensors

The magnetic field of the unshielded sensor covers a larger volume around the head of the coil. By adding a shield (a metal jacket around the sides of the coil) the magnetic field becomes smaller, but also more directed. Shields will often be available for inductive sensors to improve their directionality and accuracy.

Reference:  Automating Manufacturing Systems with PLCs – Hugh Jack

About Author //


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on

One Comment

  1. alberto alvarez
    Apr 28, 2014

    Hola,soy permanente visitante de la pagina electrical-engineering y consulto como puedo proceder a bajar documentos,articulos y tambien el contenido preferentemente en Español,si existe un procedimiento incluido en el sitio ,etc Me dara una considerable facilidad y velocidad en la lectura e interpretacon de los textos. Gracias ,atte. alberto alvarez electrical engineers.

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