Sunwu SD-05N — Inductive Proximity Switch | NPN NO | 5mm Sensing | DC 10–30V | New Original

The SD-05N is a compact inductive proximity switch from Sunwu, a Chinese manufacturer that has built a solid reputation supplying proximity sensors to machine tool, injection molding, and automation OEMs across Asia. The "SD" series is their standard cylindrical inductive line — widely used in CNC machine tool auxiliary systems, conveyor lines, and packaging equipment where a reliable, cost-effective proximity detection solution is needed.

The SD-05N specifically is an NPN, normally-open output sensor with a 5mm nominal sensing distance for standard mild steel targets. It operates on a 10–30V DC supply and uses a standard 3-wire connection compatible with most PLC input cards configured for NPN (sinking) digital inputs.

✅ Genuine Sunwu. New original. Suitable for direct PLC input wiring.

Part Number Breakdown

SD — Sunwu's standard cylindrical inductive proximity sensor series.

05 — 5mm nominal sensing distance. This is the rated detection distance for a standard flush-mounted sensor against a mild steel target (Fe360, surface area ≥ sensing face area). Non-ferrous metals (aluminum, brass, copper) reduce this distance by a material correction factor — aluminum is approximately 0.4× (effective range ~2mm), brass ~0.5×.

N — NPN output type. The output transistor pulls the signal line to ground (0V) when the target is detected. NPN sensors are standard for PLC input cards in Asia and Europe that use sourcing (PNP-powered) input circuits. For PLC cards wired for NPN inputs, connect the sensor's output wire to the input terminal and the sensor's +V wire to the card's common.

Technical Specifications

Parameter	Specification
Model	SD-05N
Manufacturer	Sunwu
Sensing Type	Inductive (electromagnetic eddy current)
Output Type	NPN, Normally Open (NO)
Nominal Sensing Distance	5mm (Sn, for mild steel)
Assured Sensing Distance	4mm (90% reliability per standard)
Supply Voltage	DC 10–30V
Load Current (max)	200mA
Residual Voltage (ON)	< 3V
Leakage Current (OFF)	< 0.5mA
Short Circuit Protection	Yes
Reverse Polarity Protection	Yes
Response Frequency	~500–1000 Hz (typical for this class)
Housing	M12 cylindrical, stainless steel barrel
Cable	3-wire, PVC sheathed, ~1–2m standard length
Protection Rating	IP67 (dust-tight, temporary immersion)
Operating Temperature	–25°C to +70°C
Target Material	Ferrous metals (Fe360 standard); reduced range for non-ferrous
Condition	New Original

NPN vs PNP — Wiring It to Your PLC Correctly

This is the most common source of SD-05N installation errors. The choice between NPN and PNP affects how you connect the sensor output to the PLC input card, and connecting it wrong doesn't just fail to work — it can damage the input card in some cases.

NPN (this sensor) — the output transistor connects the signal wire to 0V (GND) when the target is detected. The PLC input card must be a sourcing (PNP-powered input) type that provides +24V to the input terminal and detects a pull to GND as the active state. Wiring: brown wire → +24V, blue wire → 0V (GND), black wire → PLC input terminal.

PNP — the output transistor connects the signal wire to +V when the target is detected. The PLC input card must be a sinking (NPN-powered input) type. Wiring is reversed at the output wire.

If your PLC input cards are the Mitsubishi FX series, Omron CJ/NJ, or Siemens ET 200 with standard 24VDC inputs configured for NPN sensors, the SD-05N wires directly without any interface. If your PLC uses PNP sensors as standard (common in some Schneider and Beckhoff configurations), you'll need the SD-05P version instead.

Flush vs Non-Flush Mounting — Does It Matter for the SD-05N?

The SD-05N is a flush-mountable sensor — it can be installed with the sensing face flush with (or recessed into) a metal bracket or mounting hole without significantly reducing the sensing distance. This is because the internal coil design focuses the electromagnetic field forward, with good side-shielding from the metal housing.

Non-flush (unshielded) sensors have a larger sensing range but cannot be mounted in metal without mutual interference — they require clear space around the barrel equal to 2× the sensing diameter. For most machine tool and conveyor applications where sensors mount in metal brackets, the flush-mount type (like the SD-05N) is the practical choice.

Real-World Use Cases

CNC machine tool homes and limits — the SD-05N is widely used for axis home position detection and over-travel limit switching on machining centers, lathes, and grinding machines. The 5mm sensing range and M12 housing fit standard machine tool sensor mounting brackets directly.

Injection molding mold close/open detection — mold position sensing at the tie bar or platen, where the target is the moving platen in a metal-on-metal environment that would destroy mechanical switches quickly.

Conveyor part detection — detecting metal parts on conveyor belts at counts up to ~500 parts/minute given the response frequency of the sensor.

Robotic cell workpiece presence — confirming metal workpiece presence in a fixture before the robot begins a welding or machining cycle.

Packaging machine cam position — detecting cam lobe position on rotary packaging machines for synchronization with servo axes.

❓ FAQ — Sunwu SD-05N

Q1: What is the actual sensing distance — is it really 5mm for all metals?

The 5mm nominal sensing distance applies to mild steel (Fe360) targets with a surface area at least as large as the sensor face, at 23°C ambient temperature. For other metals, apply these correction factors: stainless steel ~0.9× (≈4.5mm), aluminum ~0.4× (≈2mm), brass ~0.5× (≈2.5mm), copper ~0.4× (≈2mm). If your target is aluminum and the mounting gives you 3mm clearance, a 5mm rated sensor won't reliably detect it — you'd need a longer-range sensor rated for your metal type.

Q2: The sensor is NPN — how do I wire it to a Siemens S7-1200 digital input?

The S7-1200 DI module (6ES7 221 series) supports both NPN and PNP sensors by selecting the input type via configuration in TIA Portal. For NPN wiring: brown wire → 24V DC (+M), blue wire → 0V (M), black output wire → the input terminal (I0.0 etc.). In TIA Portal, set the input channel type to "Current sourcing (PNP)" — counterintuitive naming, but this is how Siemens describes a sourcing input that works with an NPN-output sensor. If the input doesn't respond, check that the channel isn't configured as "Current sinking (NPN)" which is the reverse arrangement for PNP sensors.

Q3: What's the IP67 rating — can this sensor handle coolant spray in a machine tool environment?

IP67 means the sensor is dust-tight and protected against temporary immersion up to 1 meter for 30 minutes. In practical terms, this handles cutting fluid mist, direct coolant spray, and washdown cleaning without moisture ingress to the housing. It is not rated for continuous submersion or high-pressure jet washing (which would require IP68 or IP69K). For CNC turning centers with flood coolant, IP67 is adequate for most mounting positions — as long as the sensor isn't installed directly in a coolant channel or flood pool. The cable entry seal is part of the IP rating; if you extend the cable or cut and re-splice it, you'll compromise the rating unless you use IP-rated connectors.

Q4: What does "normally open" mean for the SD-05N output?

"Normally open" (NO) means the output transistor is off (no signal to PLC) when no metal target is in range — the "normal" state with no target present is an open circuit. When a target approaches within sensing distance, the transistor switches on, pulling the output wire to 0V (NPN), and the PLC reads the input as active/high. For most presence detection and home position applications, NO is the standard choice. A "normally closed" (NC) variant would work the opposite way and is used in safety-critical applications where a sensor cable break must be detectable as a fault (cable break looks like "no target" on an NC sensor, which triggers the alarm).

Q5: Can I use the SD-05N to detect the teeth of a gear for speed measurement?

Technically yes, but with limitations. The SD-05N has a response frequency in the range of 500–1000Hz, which corresponds to a maximum detection rate of 500–1000 target edges per second. For a gear with 60 teeth rotating at 500 RPM, the tooth frequency is 60 × 500/60 = 500 Hz — right at the sensor's limit. At higher speeds, some tooth events may be missed. For gear tooth speed sensing applications, look for proximity sensors specifically rated for high-frequency response (5000 Hz or higher) — there are dedicated gear tooth sensors in the same M12 form factor.

Q6: What's the difference between the SD-05N and SD-05N2 (as mentioned on the product page)?

The "2" in SD-05N2 typically indicates a cable length variant or minor housing revision — the core specification (NPN, 5mm sensing, 10–30VDC) is the same. Sunwu uses this suffix convention to distinguish standard cable length (1m or 2m) from other configurations. If you're replacing an existing SD-05N2 in a machine, the SD-05N is electrically identical and will function as a direct replacement; you may need to adjust cable routing if the cable length differs.

Q7: Is Sunwu a reliable brand for industrial use, or is this a low-quality sensor?

Sunwu occupies a middle tier in the Chinese proximity sensor market — above the lowest-cost no-name sensors (which often fail IP ratings and have poor repeatability) but below premium Japanese and European brands like Omron, Keyence, and Sick. In typical machine tool and conveyor applications with standard target materials and moderate ambient temperatures, SD-series sensors perform reliably for several years of continuous operation. They're a common choice for domestic Chinese machine builders and OEMs supplying mid-range equipment. For safety-critical detection or extreme temperature environments, a premium brand with full certification documentation may be more appropriate. For general automation in standard conditions, the SD-05N provides good value.

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