Like the original, today's Ethernet interfaces, often referred to worldwide as RJ45, are modular connectors with a maximum number of eight pins, all of which are equipped with contacts (8P8C = 8 pins, 8 contacts). However, today's connectors have neither the pin assignment nor the insulator in common with the RJ45S (RJ = registered jack) telephone interface registered by the Federal Communication Commission (FCC) in the USA in the 1970s. And instead of being used in private telephone systems, today's connectors are used in almost all network devices. From DSL routers and smart TVs to heating controls, intelligent Ethernet-capable devices have been equipped with this compact data interface for decades.

The global availability, the wide range of variants and the low price level of the device and cable connectors are among the reasons for their widespread use. However, ever new areas of application with increasing data transmission rates, frequencies and security requirements are pushing the RJ45 connector to the limits of its mechanical and physical transmission capabilities.

So how can a data interface initially designed for home and office applications be made suitable for industrial use without violating the standard specifications?

High demand for RJ45

In industrial communication, the proportion of Ethernet-based communication systems replacing fieldbuses is growing rapidly. According to a study by HMS Networks, the market share of industrial Ethernet systems was 59% in 2019 - with an annual growth rate of 20%. As the number of communication participants increases, so does the number of necessary data interfaces, meaning that the demand for industrial-grade RJ45 connectors is enormous.

There are now countless versions of RJ45 sockets for direct mounting on the PCB: The initially unshielded variants were quickly followed by fully shielded connectors with gold-plated contacts, which are intended to meet the requirements of the industrial environment. However, there are always compatibility problems between RJ45 connectors and sockets from different manufacturers. In applications with high mechanical loads or strong vibrations, different spring contact types and arrangement variants within the sockets often lead to contacting errors. Stable Ethernet communication between the field devices is therefore no longer possible.

Large tolerance ranges

Such compatibility deficiencies are ultimately also due to the large tolerance ranges in the RJ45 standard. The physically implemented contact system has a significant influence on the contact quality between the connector and socket - the standard merely provides a normative framework that does not offer the necessary security for all applications.

Cable and device connectors in the 'RJ45 Industrial' series have been designed for industrial and semi-industrial applications.

© Phoenix Contact

For this reason, various manufacturers have developed more robust contact systems for industrial use. The M12 or push-pull variants from Phoenix Contact are also among them. Due to their choice of materials, their locking design and their mechanically stable grommet housings, these variants are superior to the standard RJ45 system in terms of reliability, robustness and protection class. However, as they have been specially designed for IP-protected areas, they are 'oversized' for industrial applications without increased protection against dust, dirt or splash water.

Phoenix Contact has developed a robust design for cable and device connectors called 'RJ45 Industrial' for these areas of application.

In order to achieve optimum contact pressure and contact overlap between the plug and socket contacts, the developers have realigned the mating depth of the connector to the spring contacts of the socket. The result is a higher contact normal force and better mechanical stability in the mated state as well as - resulting from this - a higher tolerance to loads such as vibrations or tensile forces. Additional stability is provided by two special pressure springs on the cable connector. These are located on the top of the connector next to the latching hook and improve the contact pressure when mated. This further minimizes the tolerance differences between the connector and socket, which can lead to contact interruptions under high mechanical loads.

Shield contacts increase reliability

As device interfaces in industry are often subject to increased mechanical stress due to vibrations or tensile forces on the cable, Phoenix Contact has also equipped the sockets of the 'Industrial' series with shielding contacts. These contacts are primarily used to shield the signal pins from electromagnetic influences and to continue this shielding into the device design without interruption. A positive side effect is that they also increase the mechanical stability to the PCB and thus offer improved protection even in the event of permanent vibrations.

In addition to improved electromechanical properties, the connectors offer higher temperature resistance compared to conventional RJ45 interfaces. The glass fiber-reinforced high-temperature plastic used is designed for operating temperatures from -40 to around +100 °C. On the one hand, this is relevant when high external temperatures are present, for example in production lines. On the other hand, high temperatures and temperature fluctuations can quickly occur with high packing densities in the device itself or in the switch cabinet due to the lack of air circulation. Materials with high expansion coefficients are more susceptible to these influences and therefore cannot guarantee electrical function to the same extent.

Optional hybrid LEDs allow users and maintenance personnel in the field to easily check the status of the data interface and thus the function of the device. The combination of two pairs of LEDs - one yellow and one green - enables flexible visualization of the electrical function and the active data connection depending on the programming of the device.

Author:
Tim Kindermann is Product Manager Data Connectors in the 'Field Device Connectors' business unit at Phoenix Contact in Blomberg.