M12 Connector or Fixed Cable: Choosing the Sensor Termination

Every proximity sensor comes terminated one of two ways: a fixed cable moulded into the body, or a short pigtail ending in an M12 connector that mates with a separate cordset. People pick whichever the catalogue shows first. It is worth thirty seconds of thought, because this choice decides how the sensor fails and how long it takes to put right.

Note that an M12 connector is unrelated to an M12 barrel. A sensor with an M30 body can have an M12 connector, and frequently does.

Specify the connector when

• The sensor is removed for changeovers. On tooling that changes between products, a connector means unplugging rather than rewiring.
• Replacement time matters. A connectorised sensor is changed in two minutes by a shift fitter. A hard wired one means tracing the cable back to a junction box, and on a large machine that is an hour with a wiring diagram.
• The sensor is in a vibrating or flexing location. The cordset takes the abuse and is cheap to replace. Crane trolleys, moving arms, anything on a slide.
• The machine is exported or built in volume. Standard cordset lengths mean the wiring harness is repeatable and the build does not depend on cutting cable to fit.
• You want the diagnostic. Unplugging at the sensor and testing at the cordset end immediately separates a sensor fault from a cable fault, which is the first branch of our troubleshooting sequence.

Specify fixed cable when

• The sensor is fitted once and left. A position sensor inside a guarded enclosure that is opened at annual shutdown gains nothing from a connector.
• There is no room behind the sensor. An M12 connector plus the bend radius of the mating cordset adds perhaps 40 to 50 mm behind the barrel. In a tight pocket that space does not exist.
• The environment attacks connections. A properly moulded cable entry has no joint to fail. In continuous washdown, chemical mist or heavy dust, a fixed cable in the exact length needed removes the one component most likely to let water in.
• You want to eliminate a junction. Ordering the cable at the length that reaches the panel means no junction box, no terminal block, and two fewer places for a loose connection.

On that last point, we supply fixed cable at specified lengths rather than only standard ones. On a machine build it is usually worth asking, because it tidies the harness and removes connections.

Pin out

A three wire DC sensor on a four pin M12 uses:

• Pin 1 brown, positive supply
• Pin 3 blue, negative supply
• Pin 4 black, output
• Pin 2 white, second output on four wire parts, unused on three wire

This is standard across manufacturers, which is the main practical benefit of connectorising: a cordset from any supplier mates correctly. The colour convention matches the flying lead version, so a plant that mixes both does not need two wiring conventions. See two, three and four wire wiring.

Cordset selection

The cordset is a real component and specifying it carelessly undoes the benefit.

• Straight or right angle. A right angle connector saves the bend radius behind the sensor and is often the only thing that makes a connector fit.
• Jacket material. PVC for general use, PUR where there is oil or abrasion, and for continuous flexing on a drag chain specify a cable rated for it. Standard PVC in a drag chain fails within months.
• Shielded or unshielded. Where the cable runs alongside VFD output cabling, use shielded and earth the shield at the panel end only.
• Ingress rating. The connection is only as good as the mating. An IP67 sensor with a hand tightened connector is not IP67. Torque the coupling nut properly, and in washdown areas check that the cordset is rated to the same standard, see IP ratings explained.

The cost comparison people get wrong

A connectorised sensor plus a cordset costs more than a sensor with a fixed cable. That is the comparison usually made, and it is the wrong one.

The right comparison includes the cost of the second failure. One unplanned stop traced back to a chafed cable, on a line worth anything per hour, pays for connectorising every sensor on the machine. On a lightly loaded machine in a clean room the fixed cable genuinely is cheaper over the life. Decide per position rather than per plant.

Ordering

Both terminations are available across the D30C inductive, D31C photoelectric and capacitive ranges. Tell us which you want when you enquire, along with the cable length if you want it cut to size. The ordering code guide covers the rest of the specification.