Proximity Sensor Sensing Distance Chart: M6.5 to M50 Compared

Sensing distance scales with barrel diameter. That is the single rule behind most selection decisions, and once you have the table in front of you the choice usually makes itself.

These are the rated distances across our inductive range, measured against a standard mild steel target.

The table

Body	Thread	Shielded	Unshielded	Typical use
M6.5	M6.5	1 mm	2 mm	Grippers, end effectors
M8	M8 x 1	1 mm	2 mm	Tool changers, tight mechanisms
M12	M12 x 1	2 mm	4 mm	Indexing, small actuators
M18	M18 x 1	5 mm	8 mm	General plant workhorse
M30	M30 x 1.5	10 mm	15 mm	Heavy plant, conveyors, mills
M36	M36	On request	20 mm	Large standoff, AC two wire
M50	M50	On request	30 mm	Maximum standoff

Shielded or unshielded

The two columns are not just different distances, they are different parts with different mounting rules.

Shielded parts have a metal collar around the coil that focuses the field forward. They can be mounted flush in a metal bracket. You lose sensing distance and gain installation freedom.

Unshielded parts radiate sideways as well as forward. They sense further and must stand proud of the bracket with a clear zone around the face of roughly three barrel diameters. Fit one flush in steel and it will read permanently on. Our full comparison is in shielded against unshielded.

Three corrections before you use these numbers

The table gives rated distance. The gap you build to is smaller, for three reasons that stack.

1. Design margin. Rated distance is nominal. Effective distance allows for manufacturing tolerance, and assured operating distance allows for tolerance, temperature and supply variation together. Set the gap at 70 to 80 percent of rated and you are inside assured distance with room to spare.

2. Target material. Mild steel is the reference at 1.0. Everything else reads short:

• Stainless steel, roughly 0.7 to 0.85 depending on grade
• Brass and bronze, roughly 0.4 to 0.5
• Aluminium, roughly 0.35 to 0.45
• Copper, roughly 0.3 to 0.4

The reduction factor table has the detail. This is the most common reason a correctly specified sensor does not work.

3. Target size. The rated figure assumes a standard target at least as large as the sensor face. A smaller target reads short. If you are sensing a bolt head or a thin flag, allow for it or make the flag bigger, which is usually the cheaper fix.

A worked example

You need to sense a stainless steel cam at a gap of 6 mm, and the bracket can move about a millimetre.

Start with the gap plus the movement, so 7 mm worst case. Divide by the stainless factor of 0.75, giving roughly 9.3 mm of mild steel equivalent. Divide by 0.75 for design margin, giving roughly 12.5 mm of rated distance needed.

From the table, M30 unshielded at 15 mm covers it. M30 shielded at 10 mm does not. If the clear zone for an unshielded part is not available, you need to move the bracket closer or go to M36.

That arithmetic, done at the drawing stage, prevents most of the sensor failures we are asked about.

Other technologies in the same bodies

Inductive is not the only option in these barrels. Capacitive parts sense plastic, glass, grain and liquid, at 10 mm in M30. Photoelectric parts in M18 and M30 reach from 100 mm to 20 m depending on mode. If the inductive table does not give you the distance you need, the answer is often a different technology rather than a bigger barrel.