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Eddy current principle

If voltage is applied to the coil (1) of an inductive proximity sensor, it will generate an electromagnetic field (2) around the sensor surface. If a metallic object (3) moves into the field, eddy currents will occur in the metal [4] that weaken the magnetic field. If this happens, the metal will be detected.

Advantages and applications:

  • Reliable detection of small objects
  • Maximum range to steel (St37). Correction factors for other metals required.

Pulse technology

A direct current flows through the sensor coil and generates an electromagnetic field there. This coil current is switched on and off (pulsed) at a high frequency, so that the electromagnetic field builds up and decays in a predictable way. If a metallic object approaches the sensor, the decay behaviour changes, and the sensor output switches.

(1) Sensor output
(2) Induced voltage
(3) Metallic object
(4) Decay behaviour
(5) Time window for evaluation

Advantages and applications:

  • Longer range than Kplus sensors and sensors based on eddy current principle
  • This technology is applied for non-flush full-metal sensors from ifm.