Technical Data · Publication PROX-TD001 · Rockwell Automation
Allen-Bradley Inductive Proximity Sensors — Specifications (Bulletin 871/872)
Complete technical-data reference for Allen-Bradley inductive proximity sensors in Bulletins 871, 872, and 802PR. Covers tubular (M8 – M30 barrel), rectangular flat-pack, limit-switch, VersaCube, cylinder, and ring form factors; shielded (flush-mountable) and unshielded (extended sensing); AC and DC variants; NPN, PNP, 2-wire, 3-wire, and 4-wire complementary outputs; and weld-field-immune, ferrous-selective, and long-range options. Sensors detect metal targets with no physical contact via an oscillating electromagnetic field and eddy-current damping.
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Specifications
Sensing Performance
| Barrel diameters (tubular) | 6.5 mm, 8 mm, 12 mm (M12×1), 18 mm (M18×1), 30 mm (M30×1.5) |
|---|---|
| Nominal sensing distance — 12 mm, shielded (flush) | 2 mm (871C / 871T AC / 871T DC / 871TM N.O.) |
| Nominal sensing distance — 12 mm, unshielded (non-flush) | 4 mm (871T DC / 871TM) |
| Nominal sensing distance — 18 mm, shielded (flush) | 5 mm (871C / 871T / 871TM) |
| Nominal sensing distance — 18 mm, unshielded (non-flush) | 8 mm (871T / 871TM) |
| Nominal sensing distance — 30 mm, shielded (flush) | 10 mm standard (871C, 872C shielded); 15 mm unshielded (871TM) |
| Nominal sensing distance — 872C long range | 22 mm (30 mm shielded) up to 40 mm (30 mm unshielded) |
| Standard target | Mild-steel square, 1 mm (0.04 in.) thick, side length = face diameter or 3 × Sn (whichever is greater) |
| Operating distance, assured (Sa) | 0 … 81 % of rated operating distance per IEC 60947-5-2 |
| Repeatability | ≤ 5 % at constant temperature (871TM DC, 872C); ≤ 10 % typical (871C, 871T AC/DC); ≤ 2 % (872C 2-wire DC) |
| Hysteresis (differential travel) | 10 % typical; 15 % typical on 871TM weld-field-immune |
| Switching frequency | 10 Hz (4-wire ferrous-selective) … 2000 Hz (872C 2-wire DC 12 mm shielded); style- and barrel-dependent |
| Target correction factors (from mild-steel 1.0) | Stainless steel ≈ 0.85; Brass ≈ 0.50; Aluminum ≈ 0.45; Copper ≈ 0.40 (ferrous-selective models detect only steel) |
Electrical — DC Variants (871T, 871TM, 872C)
| Operating voltage | 10 … 30V DC |
|---|---|
| Voltage drop | ≤ 1V typical (871T 3-wire DC); ≤ 2V at 200 mA (871TM); ≤ 6V (872C 2-wire DC) |
| Load current | ≤ 100 mA (872C 2-wire); ≤ 200 mA (871TM 3-wire DC); ≤ 300 – 400 mA (871T 3-wire DC) |
| Leakage current (off-state) | ≤ 0.1 mA (871TM, 871TM weld field immune); ≤ 0.9 mA (872C 2-wire); ≤ 10 µA (871T 3-wire DC) |
| Output type | NPN sinking or PNP sourcing; Normally Open (N.O.) or Normally Closed (N.C.); complementary 4-wire available on 871T ferrous-selective |
| Protection | Reverse polarity, short-circuit (trigger ≈ 340 mA typical on 871TM), false pulse, transient noise, overload |
| IO-Link (871TM 3-wire DC standard range, N.O. PNP only) | IO-Link V1.1, COM2 38.4 kBd, 8 ms min cycle time, SIO fallback on pin 4 |
Electrical — AC Variants (871C, 871T AC)
| Operating voltage | 20 … 250V AC (871C); 20 … 132V AC (871T AC 2-wire, 4-wire ferrous-selective) |
|---|---|
| Load current | 5 … 200 mA (871C 12 mm); 5 … 250 mA (871C 18 / 30 mm); ≤ 300 – 500 mA (871T AC) |
| Inrush current (one cycle) | ≤ 2 A (12 mm); ≤ 4 A (18 / 30 mm); ≤ 3 – 5 A (871T AC) |
| Leakage current | ≤ 1.5 mA (871T AC); ≤ 1.7 mA (871T ferrous-selective); ≤ 1.9 mA at 120V AC (871C) |
| Voltage drop | ≤ 10V at 5 … 200 / 250 mA (871C); 6.5V AC at 500 mA, 10V AC at 20 mA RMS (871T AC) |
| Protection | False pulse, transient noise, short-circuit with overload trigger at 250 – 320 mA typical (871C) |
| Output | 2-wire switching (series with load); N.O. or N.C.; complementary N.O. + N.C. available on 871T 4-wire ferrous-selective |
Mechanical & Environmental
| Housing material | Nickel-plated brass (871C, 872C); 303 stainless steel (871T, 871TM); plastic face PBT; chrome-plated brass on 872C long-range |
|---|---|
| Construction | Shielded (metal band around ferrite coil — flush-mountable in metal) or unshielded (non-flush, longer sensing distance, requires metal-free zone) |
| Enclosure rating (NEMA) | NEMA 1, 2, 3, 3R, 4, 4X, 6, 6P, 12, 13 (style-dependent) |
| Enclosure rating (IEC) | IP67 standard (871C, 871T, 872C); IP68 / IP69K on 871TM short-barrel and 871TM weld-field-immune; 1200 psi (8270 kPa) washdown on ToughLink / micro variants |
| Operating temperature | -25 … +70 °C (-13 … +158 °F) standard; -40 … +70 °C (-40 … +158 °F) on 871T DC; 0 … +70 °C (32 … +158 °F) on 871T ferrous-selective; -25 … +85 °C (-13 … +185 °F) on 871TM weld-field-immune |
| Shock | 30 g (1.06 oz), 11 ms duration |
| Vibration | 55 Hz, 1 mm (0.04 in.) amplitude, 3 planes (per IEC 60068-2-6) |
| Weld-field immunity (871TM WFI / 871Z / 871ZT) | ≤ 40 mT (400 Gauss) — resistant to weld splatter and high EMF from nearby welding current |
| Status indicator | Red LED (output energized) standard; green (power); 360° visibility on 872C and 871TM; yellow flashing 80 – 100 % range indicator on 871TM standard range |
Connection & Cordsets
| Cable style | 2 m (6.5 ft) or 3 m (10 ft) PVC, 2 / 3 / 5 conductor; 2 m ToughLink (C2 / H2) on 871TM |
|---|---|
| Quick disconnect — 3-pin mini (AC) | 7/8-16 UN-2A thread; 871C, 871T AC |
| Quick disconnect — 4-pin mini (DC) | 871T DC, 871TM mini QD |
| Quick disconnect — M12 micro (DC) | Most 871TM, 872C, 871TM weld-field-immune |
| Quick disconnect — M8 Pico | 871TM 8 mm weld-field-immune, 872C long-range 6.5 / 8 mm |
| Recommended cordsets | 889N-F3AFC-6F / -F4AFC-6F (mini 3/4-pin 6 ft); 889D-F4AC-2 (M12 micro 2 m); 889P-F3AB-2 (Pico 2 m); 889R-F3ECA-2 (AC micro) |
Catalog Number Format
How to read an Allen-Bradley 871 catalog number. Each position encodes a specific configuration attribute.
Position
Meaning
Example
871 / 872 / 802PR
Bulletin number — 871 is the broad inductive-sensor family; 872 is the WorldProx line; 802PR is the pre-wired limit-switch style
871C-A2N12-A2 → Bulletin 871
Second letter (C / T / TM / TS / Z / ZT / F / FM / L / P / D / R)
Form factor — C=nickel-brass tubular, T=stainless tubular, TM=short-barrel stainless tubular, TS=food/beverage, Z/ZT=weld field immune, F=flat pack / puck, FM=mini flat pack, L=limit switch style, P=VersaCube, D=cylinder, R=ring
871T = stainless-steel barrel tubular; 871P = VersaCube or can sensor; 871R = ring sensor
-A / -D / -G / -H / -M / -N (leading suffix letter)
Electrical class — A/C=AC 2-wire, D=DC 3-wire short barrel, G=AC normally open, H=AC normally closed, M=weld field immune, N=M-series
871C-A2… = AC 2-wire; 871T-R… = DC 3-wire NPN; 871T-L… = DC 3-wire PNP
Sensing-distance digit (2 / 3 / 4 / 5 / 8 / 10 / 15 / 22 / 40)
Nominal sensing distance in millimeters
A2N12 → 2 mm; A5N18 → 5 mm; A10C30 → 10 mm; N20NN18 → 20 mm
N / P (output polarity)
N = NPN sinking output; P = PNP sourcing output (DC models only)
871TM-DH5NN18 = NPN; 871TM-DH5NP18 = PNP
12 / 18 / 30 (barrel size)
Barrel diameter in millimeters corresponding to M12, M18, or M30 thread
871T-R2A12 = 12 mm barrel; 871TM-DH10NN30 = 30 mm barrel
Trailing -A2 / -C2 / -H2 / -N3 / -N4 / -D4 / -P3 / -R3
Cable or connector suffix — A2 = 2 m PVC cable, C2 = ToughLink cable, N3 = 3-pin mini QD, N4 = 4-pin mini QD, D4 = M12 4-pin micro QD, P3 = Pico QD, R3 = AC micro QD
871C-A2N12-N3 = mini QD; 871TM-DH5NP18-D4 = M12 micro QD
Communication Protocols
Supported industrial networks and field buses for the products covered by this publication.
IO-Link V1.1 Available on 871TM 3-wire DC standard-range tubular sensors (Normally Open, PNP models only). COM2 38.4 kBd, 8 ms minimum cycle time, with SIO (standard I/O) fallback on pin 4. Enables parameter configuration, advanced diagnostics, and remote teach on an IO-Link master port.
2-wire series / parallel AC and 2-wire DC models (871C, 871T AC, 872C 2-wire) connect in series with the load; multiple sensors can be series- or parallel-connected subject to leakage-current and voltage-drop limits (see PROX-TD001 p.7).
Discrete I/O (SIO) Standard digital input signal — NPN sinking or PNP sourcing, Normally Open or Normally Closed, wired directly into PLC input modules (e.g., 1734-IB8, 5069-IB16, 1492-IFM20F-FS24 interface modules).
Certifications & Compliance
cULus Listed (UL 508 / CSA C22.2) — all applicable regulations
CE marked for all applicable EU directives (EMC, LVD)
UKCA marked for all applicable UK regulations
IP67 per IEC 60529 (all families); IP68 / IP69K on 871TM short-barrel and weld-field-immune models
NEMA 1, 2, 3, 3R, 4, 4X, 6, 6P, 12, 13 (per NEMA 250)
IEC 60947-5-2 inductive proximity switch standard (operating-distance definitions)
DIN EN 50010 switching-frequency measurement
Document Contents
Full PDF covers the following topics in detail:
- Technical definitions and terminology (active face, operating distance assured/rated, hysteresis, repeatability, shielded vs unshielded, NPN / PNP, 2-wire / 3-wire, series / parallel connection, weld-field immunity)
- Inductive proximity sensor principles of operation — ferrite-core coil + oscillator + trigger detector + output circuit; eddy-current damping of the oscillator when a metal target enters the field
- Standard target definition and target correction factors for mild steel, stainless steel, brass, aluminum, and copper
- Shielded vs unshielded spacing rules for flush and non-flush mounting in surrounding metal; side-by-side and opposed-face spacing for tubular, flat-pack, VersaCube, and limit-switch styles
- NEMA (Tables 2 – 3) and IEC 60529 IP-rating reference for hazardous and non-hazardous locations
- Tubular sensor families: 871C AC 2-wire, 871T AC / DC stainless steel, 871TS food and beverage, 871TM short-barrel / weld-field-immune / standard range, 871Z / 871ZT weld field immune, 872C WorldProx 2-wire / QuadroPlex / long range
- Rectangular families: 802PR limit switch, 871F block / flat pack / puck, 871FM miniature flat pack, 871L / 872L limit switch, 871P can sensors, 871P VersaCube multi-position
- Cylinder (871D cylinder position, 871D WorldClamp) and ring (871R) sensor families with target-size guidance
- Inductive proximity accessories: banking-screw adapters, conduit adapters, mounting brackets for tubular, can, VersaCube, and limit-switch styles; PTFE and plastic deflecting caps; mounting nuts, lock washers, spacer kits
- Torque-chart reference for sensor mounting hardware
Frequently Asked Questions
What is the difference between a shielded (flush) and unshielded (non-flush) inductive proximity sensor?
A shielded sensor has a metal band around the ferrite coil that concentrates the electromagnetic field to the front of the active face — it can be mounted flush in surrounding metal without false-triggering. An unshielded sensor has no side shielding, producing a wider magnetic field and a longer sensing distance (typically ≈ 2× the shielded equivalent for the same barrel size), but it requires a metal-free zone around the sensing face and must have no metal closer than 3× Sn opposite the face. See PROX-TD001 pages 9 – 13 for the full spacing tables.
What's the difference between the 871C and 871T 12 mm sensors?
Both are 12 mm tubular inductives with the same 2 mm shielded / 4 mm unshielded nominal sensing distance, but the housing differs: 871C has a nickel-plated brass barrel with a plastic face (2-wire AC, 20 – 250V AC), while 871T uses a 303 stainless-steel barrel (available as 2-wire AC 20 – 132V AC or 3-wire DC 10 – 30V). 871T is the correct choice for stainless-wash-down or food / beverage environments; 871C is the general- purpose AC tubular for industrial machine-tool applications.
Should I pick NPN (sinking) or PNP (sourcing) output?
NPN switches the load to the negative terminal (sinking current into the sensor output); wire the load between V+ and the sensor's output wire. PNP switches the load to the positive terminal (sourcing current out of the output); wire the load between the sensor's output and V-. The choice is determined by the PLC input module — ControlLogix / CompactLogix 1756-IB16, 1769-IQ16, 1734-IB8 all accept PNP (sourcing-type sensor, sinking input); 1756-IV16, 1769-IQ16F sink-configured modules accept NPN. In North America PNP has become the default for new designs.
When would I use an AC (2-wire) proximity sensor instead of a DC version?
2-wire AC sensors (871C, 871T AC) wire directly into AC control circuits — in series with an AC contactor coil, relay, or 120V AC PLC input module — without needing a 24V DC power supply. Use AC when the machine already has 120 / 240V AC control voltage and you want to avoid adding a DC supply, when existing relay-logic control panels need replacement sensors, or for higher switching currents (up to 500 mA on 871T AC). DC 3-wire sensors (871T DC, 871TM, 872C) are preferred for new designs — faster switching frequency (up to 2000 Hz), shorter response time, lower leakage (≤ 10 µA), and compatibility with modern 24V DC PLC input modules.
What does IO-Link on the 871TM add over a standard discrete sensor?
IO-Link V1.1 on the 871TM 3-wire DC standard-range PNP N.O. tubular models runs over the same 3-wire cable as the discrete switching signal. At power-up the sensor can operate in SIO (standard I/O) mode on pin 4 exactly like a normal PNP sensor, or an IO-Link master can switch the port into COM2 mode (38.4 kBd, 8 ms cycle) and read real-time target distance, temperature, operating hours, and switching count — plus remotely set the teach-in sensing distance. This lets you replace a failed sensor without re-teaching, push parameter configuration from the PLC, and detect gradual drift before a hard failure. Only available on the Normally-Open PNP catalog numbers (871TM-Mx…P… -D4 family).
Are these sensors suitable for weld cells with heavy EMF and spatter?
For standard inductive sensors, no — the magnetic fields from welding current will cause false triggering and molten spatter will destroy the sensor face. Rockwell offers three weld-field-immune (WFI) options: 871TM 3-wire DC WFI tubular sensors rated to ≤ 40 mT (400 Gauss) external field with stainless-steel housings resistant to spatter (IP68 / IP69K); 871Z and 871ZT weld-field-immune rectangular / tubular sensors; and PTFE or plastic deflecting caps (accessory, p.158) that can be added to standard tubular sensors to shed molten metal. WFI sensors also use a 15 % hysteresis (vs 10 % standard) to resist chatter from welding-current EMF modulation. Mounting perpendicular to the current line and placement within the "safe zone" chart (PROX-TD001 p.7) are critical.
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