Roller conveyor zone control
Twenty 2-wire M18 sensors in series down a conveyor feed a single card, with the leakage current kept under the input threshold.
Inductive · DC 2-wire, 1 – 25 mm
DC 2-Wire Inductive Proximity Sensors (M8 – M30)
Two wires in series with the load — no separate supply wire, and any number of them can be connected in series into one PLC input.
Model LJ8M-E1B / LJ8C-E2B / LJ12M-E2B / LJ12C-E4B / LJ18M-E5B / LJ18C-E8B / LJ30M-E10B / LJ30C-E15B · Brand LE Raun · Category: Proximity Sensors
Wiring2-wire
BodyM8 – M30
Sensing1 – 25 mm
ProtectionIP67
Overview
A 2-wire sensor sits in series with its load. That means no third wire back to the supply, and — more usefully — that several sensors can be connected in series to one input, which is how conveyor zone chains and multi-point door circuits are usually built.The trade-off is leakage current: a 2-wire sensor draws a small current when it is off, and a very low-impedance input can read that as ON. The sensors here are specified to stay under a standard PLC digital input threshold, but check the input on older cards.Bodies and sensing distances mirror the 3-wire range: 1 – 3 mm on M8, 2 – 8 mm on M12, 5 – 16 mm on M18, 10 – 25 mm on M30, flush and non-flush. The B suffix is normally closed, B2 normally open.
Application scenarios
Valve and actuator position on a skid
Two-wire M12 bodies confirm open and closed on a hydraulic valve bank wired back to a remote I/O box.
Door and gate position on a machine guard
M30 2-wire bodies replace mechanical limit switches without adding a wire to the door harness.
Pump and fan rotation check
An M18 body counts a bolt head on the shaft; 2-wire keeps the junction box at two terminals.
Retrofit of an existing relay panel
Replacing a mechanical switch on a 24 V circuit, the 2-wire sensor drops into the same two terminals.
Industries
- Material handling
- General machinery
- Packaging
- Building automation
Technical specifications
| Series | LJ8M-E1B · LJ8C-E2B · LJ12M-E2B · LJ12C-E4B · LJ18M-E5B · LJ18C-E8B · LJ30M-E10B · LJ30C-E15B |
|---|---|
| Body sizes | M8×45 · M12×35 / 45 / 55 · M18×55 · M30×55 / 58 / 60 mm |
| Sensing distance | 1 – 25 mm (M8: 1–3 · M12: 2–8 · M18: 5–16 · M30: 10–25) |
| Wiring | 2-wire, in series with the load — B = normally closed, B2 = normally open |
| Housing / face | Nickel-plated copper barrel, PBT sensing face |
| Operating voltage | 10 – 30 V DC |
| Switching frequency | 1.2 kHz (M8) down to 100 Hz (25 mm) |
| Repeat accuracy | < 3.0 % (Sr), < 5.0 % (Sr) on the longest ranges |
| Leakage current | Low enough for a standard PLC digital input — check the input threshold |
| Protection | IP67 |
| Current consumption | ≤10 mA |
| Output current | ≤200 mA |
| Voltage drop | ≤1.5 V |
| Hysteresis | ≤0.05 mm of the sensing distance |
| Circuit protection | Short-circuit, overload, reverse polarity |
| Cable | 2 m PVC, 3 × 0.2 mm², oil-resistant |
Dimensions
| Item | Value |
|---|---|
| Thread | M18 × 1 · M30 × 1.5 |
| Cable | Ø5 mm, 2-core |
| Mounting | Two nuts on the thread; non-flush versions leave 5 / 12 / 15 mm free |
Two-wire versions drop straight into an existing mechanical limit-switch circuit — no separate 0 V return, but the residual leakage (0.8 mA) has to be below the input card's OFF threshold.
Wiring & output
| Lead | Colour |
|---|---|
| 2 | Blue |
| 3 | Black |
| — | Two-wire types |
How to specify
- 01
Choose shielded or unshielded
A shielded (flush) sensor can be embedded in metal with only its face exposed, at about 60 % of the unshielded range. An unshielded sensor needs a free zone around the barrel but reaches further.
- 02
Size the sensing distance
Order at least 1.5 × the nominal distance to allow for tolerances, temperature and target material. Non-ferrous targets — brass, aluminium, copper, stainless — reduce the distance to roughly 30–50 %.
- 03
Match the target size
The target should be at least as large as the sensing face. A smaller target reduces the distance proportionally, so a 4 mm target on an M18 sensor will not switch at 5 mm.
- 04
Pick the output and the body
NPN / PNP, NO / NC, 3-wire or 2-wire. Plastic barrel for general use, stainless for weld fields, PTFE-faced for weld spatter, high-temperature types up to 120 °C.
Why this series
Series connection without an OR module
Ten 2-wire sensors in series still present a valid signal to one input, which is how a long line of roller zones is normally wired.
Two wires, one input card
No separate 0 V return to the sensor: the load current flows through the sensor, which halves the wiring in a panel.
Same bodies as the 3-wire range
M8 to M30, flush and non-flush, so brackets and drawings carry over from a 3-wire design.
Watch the leakage current
A 2-wire sensor leaks a small current when off. With a low-impedance input that can read as ON — check the PLC threshold before you standardise.
Questions
What is the difference between B and B2?
B is 2-wire normally closed, B2 is 2-wire normally open. Both are 2-wire; the suffix only changes the output state at rest.
How many can I connect in series?
Electrically, as many as the total voltage drop allows — each sensor drops about 2 – 3 V. Practically, keep it under ten and check the load still sees enough voltage.
Will it work on a 24 V relay coil?
Yes, provided the coil current is above the sensor's minimum operating current. Below that the sensor will not switch cleanly — use the 3-wire version.
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Standard Inductive Proximity Sensors, Short Barrel (M6.5 – M30)Proximity SensorsNeed a quotation for DC 2-Wire?
Send your application details or the guard opening dimensions and we will specify the right model and configuration for your machine.