Inductive Proximity Sensor 4mm SN04-P2 NPN Output

The SN04-P2 inductive proximity sensor 4mm is a cylindrical, contactless switch built to detect metal targets within a 4mm range. It works by generating an electromagnetic field that changes when a metal object enters it, triggering the output. Because there is no physical contact, it avoids the mechanical wear that eventually affects roller-lever or plunger limit switches.

This part suits machine builders, panel wirers and CNC hobbyists who need a dependable trigger for axis homing or end-of-travel detection. The P2 designation refers to the NPN output stage, which pulls the signal line low when a target is present — a wiring style common on many low-cost CNC controller boards.

Features of the SN04-P2 inductive proximity sensor 4mm

As an inductive proximity sensor 4mm, the SN04-P2 senses eddy currents in the target metal, so it works reliably even in dusty or oily workshop air where optical sensors struggle. The threaded M12 barrel lets you set the trigger distance by screwing it in or out, then lock it with the supplied nuts.

The output is short-circuit and reverse-polarity protected on most SN04-P2 batches, which reduces the risk of damage during wiring mistakes on a new build. Typical supply voltage is 6-36V DC, matching the rails already present in most CNC control cabinets.

• Cylindrical metal housing rated for workshop and machine-tool environments
• Detects ferrous and non-ferrous metal targets up to 4mm away
• NPN normally-open output, compatible with common DC control circuits
• No moving parts, so no mechanical contact wear over time
• Threaded body for adjustable, lockable mounting
• LED status indicator for quick on-machine diagnostics

Where it’s used

On CNC routers and mills, this inductive proximity sensor 4mm is most often fitted as a home switch on the X, Y or Z axis, giving the controller a repeatable reference point at start-up. It also works as an end-of-travel switch on gantries, or as a part-present sensor on tool changers. Builders sourcing other electrical parts for the same cabinet can browse the wider CNC parts shop for matching connectors and cables.

Outside CNC machines, the same sensor turns up in conveyor systems, packaging lines and general industrial automation, wherever a small, low-cost, contactless metal detector is needed. Its compact barrel also makes it a practical retrofit for older machines whose original microswitches have failed.

What to check before buying

Confirm the supply voltage of your controller before wiring: this inductive proximity sensor 4mm is a DC device, not suitable for AC circuits. Also check whether your breakout board expects an NPN or PNP signal, since mixing the two will stop the input triggering even though the sensor itself works correctly.

Mounting clearance matters as much as electrical compatibility. The rated 4mm sensing distance assumes a standard mild-steel target roughly the size of the sensor face; smaller targets, non-ferrous metals or off-axis approaches all reduce the effective range, so leave margin when setting the trigger position on the axis.

Installation and maintenance

Mount the sensor so the target passes straight across its face rather than at an angle, and keep the cable away from stepper or spindle wiring to avoid electrical noise. Once positioned, jam the two mounting nuts against the bracket so vibration cannot shift the trigger point. For background on the underlying detection principle, see the Wikipedia entry on proximity sensors.

Maintenance is minimal: wipe metal swarf or coolant residue off the sensor face occasionally, and check the LED indicator lights when a target passes to confirm the sensor is still triggering at the expected distance. Because there are no moving parts, a correctly wired inductive proximity sensor 4mm typically needs no adjustment for years.

FAQ

What does the 4mm in SN04 mean? It is the rated sensing distance of this inductive proximity sensor 4mm for a standard steel target directly in front of the sensor face.

Can this sensor be used with GRBL or Mach3 controllers? Yes, its NPN output is compatible with the digital inputs used for homing and limit switches on most common CNC controller boards.

Does the SN04-P2 detect non-metal objects? No, it only responds to metal targets; plastic, wood or other non-conductive materials will not trigger it.