Generic LJ12A3-4-Z/AY Inductive Proximity Sensor NPN NO, DC 6–36V, 4mm Detection, IP65

The LJ12A3-4-Z/AY features an NPN Normally Open (NO) output. In its idle state (no target detected), the output transistor is off (open circuit). When a metal target enters the 4mm sensing zone, the transistor switches on, sinking current to ground (0V). This is the most common configuration for activating PLC digital inputs. A Normally Closed (NC) version would have the opposite logic, conducting in the idle state.

No. Standard inductive proximity sensors like the LJ12A3 series are specifically tuned for ferrous metals (iron and steel). The sensing distance for non-ferrous metals like aluminum, brass, or copper is significantly reduced, often to 30-50% of the rated 4mm distance, and detection may be unreliable. For non-ferrous detection, a capacitive or specialized 'all-metal' inductive sensor is required.

Connect the brown wire to your DC power supply positive (6-36V), the blue wire to ground (0V). The black wire is the switched NPN output. To interface with a microcontroller input pin, connect a pull-up resistor (e.g., 10kΩ) from the Arduino's input pin to 5V. Connect the sensor's black output wire to the same input pin. When the sensor detects a target, it will pull the input pin low to ground through the internal transistor.

A 'shielded' (or flush-mountable) sensor, like this LJ12A3 model, has its sensing face surrounded by a metal ring. This allows it to be installed flush with or embedded into a metal mounting bracket without the bracket itself triggering a false detection. An 'unshielded' sensor requires a clearance zone around its sides. For precise positioning in metal fixtures, the shielded design is essential.

The cable is a fixed, integral part of the sensor housing and is not designed to be removed or field-replaced. The cable length can be extended by splicing and soldering, but it is critical to maintain proper shielding, use a cable with similar specifications, and seal the connection thoroughly to preserve the IP65 environmental rating. For best reliability, use a sensor with the pre-attached cable length required for your application.