Homegrown products often suffer from mechanical problems: test equipment owner mailing lists claim that mechanical items cause most issues on old equipment. Using an industry-standard connector system adds versatility and increases reliability.

When it comes to well-established connectors, in addition to the DSub-connectors (commonly known from RS232), little beats the versatility of the M12 standard. Standardised initially by the IEC in 2003, the standard has since received three upgrades and is available from different vendors.

The following steps perform a practical analysis of M12 connectors using parts provided by TE Connectivity. TE is among the market-leading brands, but remember that M12 connectors are available from other vendors.

Understanding the M12 standard

When selecting a circular connector, the first step involves determining the required signals. The industry provides connectors with two to seventeen contacts.Higher-density contacts can carry many signals, limiting the number of external ports. However, care must be taken: the amount of current that can be transferred over the individual pins is directly dependent on the density of the connector. Vendors usually specify 4A of current for the four-pin versions, with larger connectors going down to 2A or (in some cases) 0.8A per pin.The next question involves coding: this way, only the correct connector can be mated to the interface. The M12 standard addresses this via a set of plastic parts that, together, ensure that the connector of the wrong type cannot be mated. The figure below provides an overview of the possibilities.

While a greenfield design can assign codes as needed, there are predefined expectations of the various connector types. For example, A-coded connectors are commonly used for sensors, DC power, and gigabit ethernet. The Profibus association tends to like the B code, whereas the C code is used for AC applications where alternating current signals are to be transferred.M12 connectors can handle signals at high speeds. The D code, for example, is usually used for 100 Mbit ethernet. If a 10 Gigabit ethernet connection is required, an X-coded connector can be used. An example is the T4171110004-001 connector provided by TE. Its data sheet contains the specifications shown in the figure.

Mating M12 connectors to PCBs and the machinery

The PCB-facing connection can be established in multiple ways. A recent design deployed the T4171110004-001 and T4171010404-001 connectors in a fashion shown in the figure. They come with untrimmed wires connecting to all kinds of wire-to-board connectors.

In addition to that, other variants are available. They mate directly to the PCB and come with the benefits inherent to this connector configuration. The document ENG_CS_1-1773701-8_M8M12_CONNECTOR_SYSTEM_2201.pdf provides an excellent overview of what is available.

Incidentally, the cables coming outside the connector are not randomly assigned. Instead, the IEC standard has laid out guidelines for the colours and the correspondences to the pins, which are obeyed by the industry.

Fleconn of China provides an excellent overview of the colour options (which change in dependence on coding and number of pins) at http://www.fleconn-china.com/newsinfo-18-M12-Connector-Coding-Pinout-Wiring-Color-Code-and-Categories-Introduction.html. 

Connectors such as the T4111001041-000 and T4112402041-000 are useful on the wire side. When torn down, their internal structure looks as pictured.

Crimping is recommended for connecting the individual wires. While a solder joint might work initially, degradation occurs as high currents flow. The actual installation is then best accomplished with a flat 2 mm screwdriver; a good example is found in the Stanley 66-052.

Many M12 connectors are certified to high IP-protection standards. Achieving these requires discipline: in the case of the part shown here, two lock nuts are required to achieve tight closure. Furthermore, insert the wires as deep as possible into the connector shell before tightening the screw. The drilling extends far behind the screw hole and should be filled with wire in all cases.

Conclusion

If a universal and rigid connector system is required, M12 is almost always a good choice. The connectors are available in various formats and often come with high-grade IP qualifications to enable their usage in critical applications.