Operation and design of inductive sensors

Baumer inductive proximity switches are non-contact electronic sensors. Inductive sensors will recognize any conducting metal target.

The oscillator creates a high frequency electromagnetic field, which radiates from the sensing face of the switch. When a conductive metal object enters this electromagnetic field, eddy currents are induced within the metal, causing a change in the amplitude of the oscillations. The result is a voltage change at the output of the oscillator, which causes the trigger to change state and alter the output state.


Digitally switching sensors are available with a PNP, NPN or Namur output; measuring sensors come with 0 … 10 V or 4 ... 20 mA.

Series switching

3-wire DC (PNP circuit shown)

The voltage drop across each conducting sensor reduces the voltage available to drive the load. The number of proximity switches which can be connected in series is therefore limited and may be worked out by summing the individual voltage drops plus the load requirement.

Parallel switching

3-wire DC

3-wire DC sensors may be connected in parallel as shown. A parallel connection, however, must incorporate a decoupling diode.