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Technology overview

All inductive sensors have the same basic components:

  • Housing – various shapes, sizes and materials of construction
  • Basic sensor element – varies depending on the technology
  • Electronics -- evaluates what the sensor detects
  • Electrical connection – provides power and signal(s)

Eddy current technology

In an inductive proximity sensor, voltage is switched in a coil (1). This creates an electromagnetic field (2) around the face of the sensor. When a metal target (3) moves into the field, eddy currents form in the metal (4). This causes the field to collapse. When the field collapses, the target is sensed.

Benefits and applications:

  • Reliable on very small targets (robust detection of metals smaller than the sensing face.)
  • Maximum sensing range on steel targets.  Correction factor required on other types of metal targets.

Kplus technology

Basic inductive technology is influenced by the target material. Some are more difficult to detect and the sensor must be moved closer to the target by a correction factor. With a novel, patented coil structure and electronics optimized for noise immunity, ifm has developed the Kplus family of inductive products that sense all metals at the same range – no correction factor!

There are two evaluation coils with a known relative field strength between UR1 and UR2. When a target enters the field, the factor between the two coils changes and causes the sensor to switch.

Benefits and applications:

  • Obtains very long sensing ranges on any target material.
  • Immune to electromagnetic fields created by the welding process.
  • Competitively priced to be your go-to switch for all of your applications.
  • Poor performance on small or thin targets (targets smaller than the sensing face.)

Pulse technology

With pulse inductive technology, direct current flows through the sensor coil and an electromagnetic field is generated around it. The coil current is switched on and off frequently (induced voltage), so the field builds up and decays on a predictable basis. When a target is present, the decay rate changes and sensor output switches.

Benefits and applications:

  • Ability to have longer ranges than Kplus and eddy current due to the amount of energy being sent into the space.
  • This is the technology used for ifm’s non-flush full metal sensors.

Magnetic principle

This principle uses standard inductive technology, but an embedded magnet allows for the most amount of energy to be transferred to the sensing face. The dampening sleeve focuses the field to very precise switch on and off points. This technology works to detect mild steel targets only.

Benefits and applications:

  • Allows for a very thick metal face to withstand pressures up to 7250 psi.
  • Best suited for high pressure applications like hydraulics and hydraulic cylinders.
  • Only works on steel targets.

Influences on sensing range

Sensing range is the mechanical distance where a metal plate approaching the sensor face axially causes the output to switch.

Our datasheets specify 3 different detection distances.

  • Sensing range refers to the nominal range defined during development and is based on a target of some standard size and material.
  • Real sensing range takes into account component deviations at room temperature and is at worst 90% of the nominal sensing range.
  • Operating distance also takes into account switch point drift due to humidity, elevated temperature, etc. and it is at worst 90% of the real sensing range. This is the distance that should be evaluated if sensing distance is critical.

In practice, targets are rarely the standard size and shape used to specify the nominal sensing range. The influence of target size is shown below.

 

Less common than target size is target shape. The images below show the general influence of shape. It is difficult to provide a correction factor based on shape, so testing should be conducted when the sensing distance is critical.

 

Finally, the major contributor to sensing range influence is the target material. Materials with less iron form smaller eddy currents and are therefore more difficult to sense. The correction factor by material is shown below.

This correction factor has no influence when using Kplus technology!