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Eddy current sensor : Operating principle and applications


Eddy current sensors are primarily used for displacement and position measurement of electrically conductive targets. They are generally used for measuring ferromagnetic and non-ferromagnetic materials. They are suitable for applications in harsh industrial environments due to their superior tolerance for oil, dirt, dust, moisture and magnetic interference fields. Available in miniature and sub-miniature models, they can also be used for measurement in a space where area is restricted. How does eddy current sensor works?

Eddy current sensor operating principle

Operating principle of eddy current sensor
Fig.1 Schematic of eddy current operating principle

Eddy current sensor operates based on the inductive eddy-current principle. It measures the distance based on the extraction of energy from an oscillating circuit, which is required to generate eddy current in an electrically-conductive materials.

When the sensing coil is supplied with an alternating current, it causes a magnetic field to form around the coil. If an electrically conducting material is placed in this field, eddy current field is induced according to the Faraday’s induction law. When the object moves, it causes the change in the impedance of the coil, which is proportional to the change in the distance between the sensor and the target.

Advantages of eddy current sensor

Eddy current sensors have superior temperature stability and resistance towards pressure, temperature, dirt and oil. Capable of operating at pressure up to 4000 bar, they are one of the best wear-free, non-contact sensors for measuring displacement and position in harsh industrial environment.

The sensors are also capable of measuring at high speed up to 100 kilo Samples per second. The sensor head can also be customized based on specific customer requests to fit in different applications. The sensors are generally miniature in size and therefore, are suitable for measuring in an area where access is restricted. These sensors are also low-cost and can be used in high-volume OEM applications.

Potential applications for eddy current sensor

Due to its resistance and stability to measure under extreme environment, eddy current sensors are used in a wide range of industrial applications. Some examples include:

  • Measure vibrations of actuators in steel galvanising plants
  • Cylinder movements in an internal combustion engine
  • Measure thickness of sheet metals in roller gap
  • Measure movement of hydraulic cylinders
  • Used in airplanes to measure movement of door lock switches and landing gear flaps

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