Inductive · ring / loop, 6 – 21 mm bore

Loop-Shaped (Ring) Inductive Proximity Sensors (6 – 21 mm bore)

A coil around a hole: anything metal that passes through is counted, down to a 0.4 mm wire, regardless of where in the bore it passes.

Model LJR-06 / LJR-08 / LJR-10 / LJR-12 / LJR-19 / LJR-21 · Brand LE Raun · Category: Proximity Sensors

Bore6 – 21 mm

Min. object0.4 mm

Frequency1 kHz

OutputNPN / PNP

Request a quote Full specifications

Overview

A ring sensor is a coil wound around a hole. Anything magnetic that passes through the hole changes the field, so the sensor counts it — regardless of where in the bore it passes, how fast it moves or whether it is round. That is what makes it the standard answer for wire, springs, needles and small fasteners, where a barrel sensor would need a precise gap and a photoelectric one would need a clear line of sight.Six bore sizes run from 6 mm to 21 mm. Always choose the smallest bore the part can pass through: the field is strongest at the centre and the minimum detectable object grows with the bore.All versions are 10 – 30 V DC, 1 kHz, under 1 ms response, ABS housing, IP67, with an orange status LED and NPN or PNP output.

Application scenarios

Wire and cable feed counting

A 0.6 mm wire through the 6 mm bore is counted once per pass, at 1 kHz, without a mechanical wheel.

Spring and needle feed on an assembly machine

The part passes through the ring and is counted regardless of orientation — the case a photoelectric sensor keeps missing.

Screw and rivet drop detection

A 21 mm bore sits under the feed tube and counts each fastener as it falls.

Broken-tool and broken-wire detection

A missing pulse means the wire broke; the 1 ms response stops the machine before the next cycle.

Needle and syringe assembly

Bore 8 mm counts cannulas as they pass, with no contact and no wear.

Industries

Wire and cable
Fastener and spring production
Medical devices
Assembly

Technical specifications

Series	LJR-06 · LJR-08 · LJR-10 · LJR-12 · LJR-19 · LJR-21
Inner bore size	6.0 · 8.0 · 10.0 · 12.0 · 19.0 · 21.0 mm
Minimum detectable object	0.4 mm ±1 %
Detected object	Magnetic metal
Response frequency	1 kHz
Response time	< 1 ms
Housing	ABS, flame-retardant
Indicator	Orange (red) LED
Ambient temperature	−25 °C – +70 °C
Operating voltage	10 – 30 V DC
Repeat accuracy	< 5.0 % (Sr)
Output	NPN (blank suffix) or PNP (P suffix)
Protection	IP67
Current consumption	≤10 mA
Output current	≤200 mA
Voltage drop	≤1.5 V
Switching frequency	0.5 – 5 kHz depending on size
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
Body	35 × 60 × 16 mm (all bore sizes)
Mounting holes	45.5 mm pitch, M4
Cable	2 m, 3-core

The body is common to all six bore sizes; only the bore changes, which is what makes a changeover a matter of one screw.

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

0.4 mm wire is enough

The field fills the whole bore, so a thin wire, a needle or a spring is detected wherever it passes through — no alignment, no focal spot.

Position-independent counting

Because the field is the bore, the part can run off-centre, vibrate or change diameter and still be counted once.

Six bore sizes

6, 8, 10, 12, 19 and 21 mm — pick the smallest bore the part will pass through, which gives the strongest signal.

1 kHz, under 1 ms

Fast enough to count parts on a high-speed feed track without a gap.

Questions

Does the part have to pass through the centre?

No — the field fills the bore. Off-centre passage still triggers it, which is why it works on a vibrating feed track.

Will it count two parts touching each other?

No. Two parts in contact pass as one object. If you need to separate them, keep a gap of at least the part diameter between them.

Can it detect plastic or glass?

No — this is an inductive sensor, magnetic metal only. For non-metal parts through a bore, use a capacitive sensor or a fibre-optic fork.

Need a quotation for Loop-Shaped (Ring)?

Send your application details or the guard opening dimensions and we will specify the right model and configuration for your machine.