What is Eddy Current Proximity Sensor?

Eddy current proximity sensors are used to detect non-magnetic but conductive materials. They comprise of a coil, an oscillator, a detector and a triggering circuit.

Eddy Current Proximity Sensor

The Figure shows the construction of eddy current proximity switch. When an alternating current is passed thru this coil, an alternative magnetic field is generated.

If a metal object comes in the close proximity of the coil, then eddy currents are induced in the object due to the magnetic field. These eddy currents create their own magnetic field which distorts the magnetic field responsible for their generation.

As a result, impedance of the coil changes and so the amplitude of alternating current. This can be used to trigger a switch at some pre-determined level of change in current.

Eddy current sensors are relatively inexpensive, available in small in size, highly reliable and have high sensitivity for small displacements.

Applications of eddy current proximity sensors

• Automation requiring precise location
• Machine tool monitoring
• Final assembly of precision equipment such as disk drives
• Measuring the dynamics of a continuously moving target, such as a vibrating element,
• Drive shaft monitoring
• Vibration measurements