As a consequence of the rapidly increasing networking of all production facilities in the course of the 4th industrial revolution, the demands on connection technology for the factory of tomorrow are increasing. In addition to reliable, secure contacting under difficult conditions (limited installation space, vibration, dirt, temperature stress, tightness), the requirements for energy efficiency, power consumption, miniaturization and electromagnetic compatibility are increasing significantly.

The user can use the derating curve to quickly draw conclusions about the current carrying capacity of the connector system.

© Belden

The L- and T-coded versions are used for applications in the low voltage range (SELV, PELV). For applications with voltages above 50 V(AC)/60 V(DC), the S and K codings are required. The latter can be used, for example, for connecting servomotors with a power range of 630 V/16 A and at temperatures of up to 125 °C. The clearances and creepage distances of the K-coded connector variants are dimensioned to withstand a rated surge voltage of 6 kV.

The L-coded connector variants, on the other hand, can be used in sensor-actuator boxes and enable continuous standardized M12 cabling. The L-coded variants are included by the Profibus & Profinet user organization in the 'Profinet Cabling and Interconnection Technology Guideline'. This variant is characterized by two circuits plus additional functional earthing, a rated current of 16 A and a size with a maximum outer diameter of 18 mm. Cabling with connectors of larger dimensions, such as 7/8-inch connectors, is therefore no longer necessary.

What has changed?

Micrograph of an M12 power contact, crimped on a 1.5 square millimeter stranded wire: It shows a gas-tight hexagonal crimp without cracking for the contour defined from the FEM.

© Belden

The requirement for the M12 power connectors to be able to transmit a rated current of 16 A with a wire cross-section of 1.5 ^mm2 in the same installation space required a new contact material and a new contact design. Among other things, the challenges for the contact material in terms of high electrical conductivity were at odds with the required mechanical material characteristics. In contrast to the previously used Ms alloys, the new contact material used by Belden therefore has a significantly higher copper content, among other things. In addition, the tension between high contact rigidity and good formability had to be resolved - using iterative FEM simulations.

The most important parameters

An important parameter for connectors and a measure of the quality of the contacting of the contact system is the current carrying capacity. It is determined by the contact heating (Joule's law) that occurs when a current flows. In a stationary load case, the current carrying capacity is described by the derating curve according to DIN EN 60512-5-2 and determined by the thermal properties of the materials used for the contacts and plastic parts. The operating temperature results from the self-heating and the ambient temperature at which the connectors can be used.

The overmolded and freely configurable versions of Belden's power connector feature a mating aid in the form of an arrow on the housing parts to enable users to quickly align the plug pins and sockets.

© Belden

The rated current specified by the manufacturer - preferably defined in accordance with DIN EN 61984 chapter 3.27 at an ambient temperature of 40 °C - is the current that the connector can carry continuously and that flows through all contacts simultaneously. In the case of the Belden solution, this is 16 A for all four coding variants. To measure the temperature, temperature sensors are attached to the warmest points and the ambient temperature is measured at the same time. Possible hotspots can be identified using thermographic images. Finally, a good contact system is characterized by an even temperature distribution over the entire connector system, including the conductor connection.

Other important parameters of a contact system are the number of mating cycles, which are specified as 100, 50 or 20 mating cycles depending on the performance level of the contact system, as well as the quality of the stress relaxation of the spring laminations. Reliable contacting is ensured if the normal contact force over the entire service life does not fall below the minimum value required to penetrate the foreign layers.

Stress relaxation can generally be observed in contact materials. This means that a live electrical contact is subject to thermal ageing at elevated temperatures, as a result of which it loses part of its contact force. The Larson-Miller parameter can be used to calculate the long-term behavior of the residual stress after thermal relaxation by showing a relationship between the stress relaxation ∆σ (%), the operating temperature and the load duration.

Compared to conventional brass materials, the copper alloy used in Belden's M12 power contacts offers significantly improved relaxation behavior, which allows the upper temperature range to be increased to +125 °C compared to the upper limit temperature of +85 °C defined in the design standard for M12 power connectors.

The wires are usually connected to the connectors using crimping technology. This means that a high-quality, gas-tight connection to the connector can also be made quickly on site using standard crimping pliers. The crimp connection is described in DIN EN 60352-2 and is essentially evaluated by the pull-out forces of the stranded wire, the contact resistance and by assessing the gas-tightness using micrographs. The standard wire cross-section for M12 power connectors is 1.5 mm2. To minimize the voltage drop with longer cable lengths, cables with 2.5 ^mm2 and the corresponding components are also available. Smaller cross-sections are also available as an option. For EMC-critical applications, the application can be set up completely with shielded components.

Author:
Uwe Widmann works in the Technology & Standardization department at Belden Germany.