PRINTABLE FIELD REFERENCE · A4 / LETTER
Industrial I/O
Pocket Card.
Designed for noisy, zero-signal plant floors. Print, fold in half, and keep inside your multimeter pouch or tape directly inside the enclosure door.
POCKET SPECIFICATION
- Dimensions: 105 × 148 mm (Folded A6) or full Letter/A4
- Target Paper: 160–250 gsm cardstock (or laminate)
- Standards: IEC 61076, IEC 61131, ISA-50, NAMUR NE 43
- Color Code: High-contrast industrial wire sequences
SIGNAL FIELD GUIDE · POCKET CARD
4–20 mALive Zero
M12/M8Wire Colors
PNP/NPNCommon Logic
24V DCDrop Budget
SIGNAL FIELD GUIDE · INDUSTRIAL I/O POCKET REFERENCE · REV 2026.1 HTTPS://SIGNALFIELDGUIDE.COM
PANEL 1
4–20 mA Current Loops & NAMUR NE 43
Loop Voltage Headroom Formula:
V_transmitter = V_supply − (I_max × R_total_loop) Transmitter terminal voltage must stay ≥ 12.0 V DC at 20.5 mA.
| Signal Level | Percentage | Diagnostic Condition (NAMUR NE 43) |
|---|---|---|
0.00 mA | Open / Dead | Broken wire, blown fuse, or dead 24V supply. |
< 3.60 mA | Under-range | Sensor failure or broken sensing element. |
3.80 mA | -1.25% | Permissible under-range baseline. |
4.00 mA | 0.0% | True Process Zero (Live Zero). |
12.00 mA | 50.0% | Midpoint span reading. |
20.00 mA | 100.0% | Full Scale Process Upper Range. |
20.50 mA | 103.1% | Permissible over-range limit. |
> 21.00 mA | Fault Short | Sensor short circuit or severe electronics fault. |
Meter Hookup: Multimeter MUST be in series with loop current. Parallel multimeter probe hookup creates a short circuit and blows the meter fuse.
PANEL 2
DC 3-Wire Sensor Switching (PNP vs NPN)
| Sensor Type | Switching Action | PLC Input Required | PLC Common Tie |
|---|---|---|---|
| PNP (Sourcing) | Switches +24 V DC to signal line | Sinking Input Card | Common terminal tied to 0 V DC |
| NPN (Sinking) | Switches 0 V DC to signal line | Sourcing Input Card | Common terminal tied to +24 V DC |
Standard 3-Wire DC Sensor Wire Colors (IEC 60947-5-2):
- Brown (BN): +24 V DC Power Supply (+19.2V to +28.8V)
- Blue (BU): 0 V DC Reference Return
- Black (BK): Switched Output 1 (Normally Open / NO)
- White (WH): Output 2 / Normally Closed (NC) / Antivalent
Ghost Voltage Trap: High-impedance digital multimeters may measure 2V–8V on an open sensor output. Use a 10 kΩ pull-down resistor or low-impedance meter (LoZ) to verify true switching.
PANEL 3
M12 & M8 Circular Connector Pinouts
| Connector | Pin 1 | Pin 2 | Pin 3 | Pin 4 | Pin 5 / FE |
|---|---|---|---|---|---|
| M12 A-4 | Brown (+24V) | White (NC) | Blue (0V) | Black (NO) | — |
| M12 A-5 | Brown (+24V) | White (Aux) | Blue (0V) | Black (C/Q) | Gray (FE / Shield) |
| M12 D-4 (ETH) | Yellow (Tx+) | White (Rx+) | Orange (Tx−) | Blue (Rx−) | Shell 360° Shield |
| M12 B-5 (DP) | +5V (VP) | Green (Line A) | 0V (DGND) | Red (Line B) | Shield Ground |
| M8 A-3 | Brown (+24V) | OMITTED | Blue (0V) | Black (NO) | — |
| M8 A-4 | Brown (+24V) | White (NC) | Blue (0V) | Black (NO) | — |
CRITICAL TRAP: Pin numbers mirror horizontally across mating faces! Looking into male pins: Pin 1 is top right. Looking into female sockets: Pin 1 is top left.
Torque Specs: M12 knurled nut: 0.6 Nm · M8 knurled nut: 0.4 Nm. Never use pliers on knurled couplings.
Torque Specs: M12 knurled nut: 0.6 Nm · M8 knurled nut: 0.4 Nm. Never use pliers on knurled couplings.
PANEL 4
Noise, RS-485 Modbus & Voltage Drop
5-Point Enclosure Noise Checklist:
- Shield Termination: Ground cable shield at ONE end only (cabinet end) for low-frequency analog loops to prevent ground circulating currents.
- RS-485 Bus Termination: Exactly two 120 Ω resistors at the two physical cable ends. Total unpowered line resistance across A & B must measure 60 Ω.
- Modbus Idle Bias: Pin 4 (Line B) must measure +0.8V to +1.2V DC higher than Pin 2 (Line A) relative to 0V ground.
- Inductive Kickback: Place a reverse flyback diode (1N4007) across DC solenoids, or an RC snubber across AC contactor coils.
- 24V DC Cable Drop Limit: Ensure sensor terminal voltage stays > 20.4 V DC under maximum inrush load.
Conductor Loop Resistance (Copper @ 20°C):
R_loop = 2 × Length (m) × Conductor Resistance (Ω/m) 22 AWG (0.34 mm²) = ~0.057 Ω/m · 18 AWG (0.82 mm²) = ~0.021 Ω/m