Short answer
Pin 1 is +24V (Brown), Pin 2 is NC/Signal 2 (White), Pin 3 is 0V (Blue), Pin 4 is NO/Signal 1 (Black).
Under industrial standard IEC 61076-2-101, the keyway orientation governs terminal positions. Always verify whether you are inspecting male pins or female contact sockets; pin sequences mirror horizontally across mating faces.
Mating face vector schematic
Compare the male plug and female socket pin positions before terminating wires or taking multimeter readings.
Physical & electrical specifications
| Specification Parameter | Standard Value | Practical Field Implication |
|---|---|---|
| Governing Standard | IEC 61076-2-101 | Guarantees dimensional interoperability between manufacturers (Siemens, Phoenix Contact, Turck, Murr). |
| Mechanical Keyway | Single polarizing keyway notch at 12 o’clock position on male plug, mating tab on female receptacle. | Prevents accidental cross-mating into incompatible communication or power ports. |
| Coupling Nut Torque | 0.6 Nm (hand-tight + 1/4 turn with knurled wrench) | Excess torque crushes the internal elastomeric O-ring, causing coolant leaks and intermittent shorts. |
| Rated Voltage | 250 V AC/DC | Maximum dielectric insulation boundary between adjacent conductor pins. |
| Rated Current Limit | 4 A per contact | Continuous current carrying capacity per pin without thermal de-rating. |
| Recommended Wire Gauge | 22 AWG to 20 AWG (0.34 mm² to 0.50 mm²) | Conductor strand cross-section required to maintain terminal contact and pull-out strength. |
| Ingress Protection | IP67 / IP68 (when properly torqued with intact O-ring) | Submersion and high-pressure washdown seal integrity when fully threaded. |
Pin assignment & multimeter test values
Measure between the designated pin and reference ground with a digital multimeter in DC Volts mode.
| Pin # | Standard Color | Signal Designation | Operating Voltage | Multimeter Test Method |
|---|---|---|---|---|
| Pin 1 | Brown (BN) | +24 V DC Power Supply | +19.2 to +28.8 V DC | DC Volts across Pin 1 (+) and Pin 3 (-). Must read nominal +24 V DC. |
| Pin 2 | White (WH) | Complementary / NC / Diagnostic Output | 0 V DC (OFF) or +24 V DC (ON) | DC Volts across Pin 2 and Pin 3. Active when sensor is unactuated on NC sensors. |
| Pin 3 | Blue (BU) | 0 V DC (Common Ground / Return) | 0.00 V DC reference | DC Volts across Pin 3 and chassis earth (<0.5 V DC). Continuity to panel 0 V bus. |
| Pin 4 | Black (BK) | Switched Output (NO) / IO-Link C/Q Line | 0 V DC (OFF) or +24 V DC (ON) | DC Volts across Pin 4 and Pin 3. Transitions to +24 V DC when target engages PNP sensor. |
Meter-first 3-step field diagnostic sequence
Perform these 3 tests in order before swapping field devices or cutting cable bundles.
- Step 1: Measure Open-Circuit Supply Voltage
Action: Unplug sensor. Set multimeter to DC Volts. Insert red lead into Female Pin 1 (Brown) and black lead into Female Pin 3 (Blue).
Expected Reading: +20.4 V to +27.6 V DC (IEC 61131-2 Type 1/3 limit).
Fault Symptom: If reading is 0V, inspect panel fuse, distribution block terminal tightness, or severed cable in drag chain.
- Step 2: Verify Output Switching Under Load
Action: Reconnect sensor using a breakout box or backprobe Pins 3 & 4. Toggle target in front of sensor face while observing meter.
Expected Reading: 0.0 V DC (target absent) -> +23.2 V DC (target present, <1.0 V drop below supply).
Fault Symptom: If output voltage stays floating (e.g., 2V to 8V), the sensor output transistor is damaged or the PLC input lacks a solid 0V common reference.
- Step 3: Inspect Drag Chain Conductor Fatigue
Action: Switch multimeter to Ohms (Audible Continuity). Measure Pin 3 (Blue) to panel 0V while manually flexing the cable along flex-points.
Expected Reading: <0.8 Ω steady continuous resistance.
Fault Symptom: Intermittent beeping or resistance jumps above 5 Ω reveal fractured copper stranding inside polyurethane jacket.
Field traps & common failure modes
Male vs. Female Face Mirroring Error
Observed Symptom: Technician replaces cordset and burns sensor internal circuit immediately upon power-up.
Root Cause: Pin numbering mirrors across mating planes: Pin 1 and Pin 2 flip horizontal orientation when looking into male pins vs female sockets.
Field Correction: Always verify terminal numbers embossed into the plastic contact carrier or check wire colors before soldering or terminating.
Over-Torquing Knurled Coupling Nut
Observed Symptom: Intermittent water ingress and corrosion faults after washdown cycles.
Root Cause: Using channel-lock pliers compresses the internal silicone O-ring past its yield point, tearing the seal.
Field Correction: Tighten knurled coupling nut to 0.6 Nm using an industry torque wrench with an M12 crowfoot attachment.
Industrial protocols & applications
| Network / Protocol | Standard Application | Reference Standard |
|---|---|---|
| Standard Discrete DC Sensors | Inductive, capacitive, and photoelectric proximity switches operating in PNP or NPN mode. | IEC 60947-5-2 |
| IO-Link Port Class A | Point-to-point digital communication on Pin 4 (C/Q) with 24V auxiliary power. | IEC 61131-9 |
| Solid-State DC Actuators | Pneumatic valve solenoid coils and stack lights pulling up to 2A continuous. | ISO 13849 |
Frequently asked field questions
What is the color code for an M12 4-pin A-coded sensor cable?
Under IEC 60947-5-2 and IEC 61076-2-101, standard M12 4-wire color code is: Pin 1 = Brown (+24V DC), Pin 2 = White (NC / Signal 2), Pin 3 = Blue (0V DC), and Pin 4 = Black (NO / Switched Output 1).
Why does an M12 4-pin sensor read 24V supply but refuse to trigger the PLC input?
The PLC input module common may be mismatched: a PNP sensor sources +24V and requires a sinking PLC input card (common tied to 0V). If the PLC card common is wired to +24V (expecting NPN), no current flows.
Tape this inside the enclosure door.
No signal on the plant floor? Get the 2-page laminated pocket card. Contains 4–20 mA NAMUR thresholds, PNP/NPN PLC common logic, M12/M8 pin numbers, and 24V DC voltage drop rules.