Short answer
Pin 1 is +24V (Brown), Pin 2 is Output 2/NC (White), Pin 3 is 0V (Blue), Pin 4 is Output 1/NO (Black).
Under industrial standard IEC 61076-2-104, 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 61076-2-104 | Guarantees dimensional interoperability between manufacturers (Siemens, Phoenix Contact, Turck, Murr). |
| Mechanical Keyway | Single polarizing keyway notch with 4 micro contact pins arranged in a tight symmetrical circle. | Prevents accidental cross-mating into incompatible communication or power ports. |
| Coupling Nut Torque | 0.4 Nm | Excess torque crushes the internal elastomeric O-ring, causing coolant leaks and intermittent shorts. |
| Rated Voltage | 30 V AC / 30 V DC | Maximum dielectric insulation boundary between adjacent conductor pins. |
| Rated Current Limit | 3 A per contact | Continuous current carrying capacity per pin without thermal de-rating. |
| Recommended Wire Gauge | 26 AWG to 24 AWG (0.14 mm² to 0.25 mm²) | Conductor strand cross-section required to maintain terminal contact and pull-out strength. |
| Ingress Protection | IP65 / IP67 | 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 Supply (L+) | +19.2 to +28.8 V DC | DC Volts across Pin 1 and Pin 3. Must measure nominal +24 V DC. |
| Pin 2 | White (WH) | Output 2 / NC (Normally Closed) / Antivalent | 0 V DC (actuated) or +24 V DC (unactuated) | DC Volts across Pin 2 and Pin 3. Active (+24V) when target is absent. |
| Pin 3 | Blue (BU) | 0 V DC Common Return (L-) | 0.00 V DC reference | Continuity to power supply 0V rail (<0.5 Ω). |
| Pin 4 | Black (BK) | Output 1 / NO (Normally Open) / Primary Signal | 0 V DC (unactuated) or +24 V DC (actuated) | DC Volts across Pin 4 and Pin 3. Active (+24V) when target is present. |
Meter-first 3-step field diagnostic sequence
Perform these 3 tests in order before swapping field devices or cutting cable bundles.
- Step 1: Verify Antivalent Complementary Output States
Action: Connect meter red probe to Pin 4 (Black) and black probe to Pin 3 (Blue). Present target. Repeat for Pin 2 (White).
Expected Reading: When Pin 4 reads +24V, Pin 2 must read 0V. When target leaves, Pin 4 drops to 0V and Pin 2 rises to +24V.
Fault Symptom: If both pins read +24V or 0V at the same time, the sensor internal logic is corrupted or outputs are shorted together.
- Step 2: Test Dual OSSD Channel Safety Synchronization
Action: On safety interlocks using M8 4-pin, measure DC Volts on Pins 2 & 4 relative to Pin 3 simultaneously while closing guard door.
Expected Reading: Both OSSD lines switch to +24V DC within 50 ms of each other (IEC 62061 disparity limit).
Fault Symptom: A timing disparity >500 ms triggers a safety relay discrepancy fault, locking out machine restart.
- Step 3: Inspect Sub-Miniature Solder Cup Shorts
Action: On field-wireable M8 4-pin plugs, test adjacent pin resistance with cable disconnected.
Expected Reading: >50 MΩ open circuit between all adjacent pins.
Fault Symptom: Due to tight 1.0mm pin spacing, stray wire whiskers frequently short Pin 1 (+24V) to Pin 2 or Pin 4, destroying PLC input optocouplers.
Field traps & common failure modes
The Antivalent (NO+NC) Sensor Replacement Mismatch
Observed Symptom: Machine cycle stops randomly; PLC displays "Sensor Discrepancy Error".
Root Cause: Technician replaced an antivalent (1 NO + 1 NC) sensor with a dual NO sensor because both have 4 pins.
Field Correction: Always check sensor catalog part number: verify whether Pin 2 is NC complementary or a second independent NO channel.
Mismatched M8 vs M12 Signal Cards
Observed Symptom: Trying to connect an M8 4-pin sensor to an M12 junction box using cheap unverified adapter leads.
Root Cause: Third-party adapter cables frequently swap Pin 2 and Pin 4 or omit Pin 2 connection altogether.
Field Correction: Ring out adapter cables pin-to-pin with multimeter continuity before installing into machine cable tracks.
Industrial protocols & applications
| Network / Protocol | Standard Application | Reference Standard |
|---|---|---|
| Dual-Output Photoelectric Sensors | Sensors providing both foreground and background suppression signals. | IEC 60947-5-2 |
| Compact Safety Door Interlocks | RFID non-contact safety door switches transmitting dual OSSD 24V pulses. | ISO 14119 |
| Ultrasonic Distance Transmitters | One switching threshold output + one continuous analog 0-10V or teach output. | IEC 60947-5-7 |
Frequently asked field questions
What is the color code for an M8 4-pin sensor cordset?
The standard IEC 60947-5-2 color code is: Pin 1 = Brown (+24V DC), Pin 2 = White (Output 2 / NC), Pin 3 = Blue (0V DC), and Pin 4 = Black (Output 1 / NO).
Can an M8 3-pin sensor cable be plugged into an M8 4-pin sensor?
Yes, but you will only have access to Pin 1 (+24V), Pin 3 (0V), and Pin 4 (NO Output). Pin 2 (White) on the sensor will remain disconnected, disabling the secondary output or diagnostic channel.
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.