2 wire Inductive proximity Switch

Discussion in 'General Electronics Chat' started by SSR, Feb 12, 2015.

  1. SSR

    Thread Starter New Member

    Aug 6, 2011

    I was reading about a 2 wire inductive proximity switch, and i am little bit confused about how the switch generates the magnetic field. The wiring for the sensor goes like this:


    Essentially all inductive sensors need to have a magnetic field to sense some metallic object, but how could the above sensor generates the magnetic field when the neutral is isolated through some load i.e the neutral has no direct connection to the coil of sensor that generates the field.

    I read some where that a small residual current flows even when there is no metallic object nearby, from the phase to normally open contact(NO) then from load and back to neutral, that creates the needed magnetic field required for sensing. Is that true?
    Last edited: Feb 12, 2015
  2. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    That's how it works, yes. An extremely amount of current flows through the load (even when no detection is taking place) for the sensing circuit to work. Once the sensor makes a positive detection, then the circuitry allows the full flow of current to pass through, effectively feeding the load.
  3. MaxHeadRoom


    Jul 18, 2013
    If you are thinking of using the 2 wire, they generally are used for high impedance input devices such as Opto inputs, PLC or MicroP type inputs, if you wish to switch any kind of higher load such as a relay etc, you need the 3 wire open collector type.