Industrial ethernet connectivity

Ethernet has played a long-term part in the networking of office PCs and peripherals, and is well proven in support of users for file sharing, printing and messaging to name but a few.

Control systems for the manufacturing and industrial arena have been the domain of RS232-type protocols with the resultant slow speeds and limited intelligence.

The entrance of industrial automation applications has led to the development of ethernet/IP for the factory floor. Still based on the proven ethernet protocols of TCP/IP and CSMA/CD and the traditional network interface cards (NICs) and interfaces, the networking needs of the factory floor, heavy industry and mining differ considerably from the office domain. While file sharing and printing in the office is not typically time sensitive with delivery, the control of robotics on assembly lines, sensing devices and the automated picking, filling and packing of product requires accurate timing and delivery of communications. In the industrial environment, ethernet/IP is expected to communicate with switches, PCs, printers, human-machine interfaces and PLC devices.

Leaving the upper layers and the active components of level 1 and 2 of the OSI model aside, the physical media of cable and connectors to be installed and used in the industrial environment require special considerations.

The industrial complex generally presents a harsher environment than that of a commercial office and therefore issues with vibration, shock, dust, moisture, temperature, corrosives, contaminates and electromagnetic interference (EMI) will be encountered. This is referred to as mechanical, ingress, climate/chemical and electromagnetic (MICE). The MICE classification is then taken to three levels:

Level 1 - Commercial

Level 2 - Light industrial

Level 3 - Harsh industrial

Connector assemblies that are able to operate in one or more of the MICE environments need to be considerably more robust than its traditional office equivalent. Expose the average office plug and jack to harsh environments and it would likely fail within a short time.

The industrial network is supported on copper and/or optical fibre cabling depending on the application and environment. Housings with suitable MICE ratings that accommodate modular plug and jack assemblies for copper and LC interfaces for optical fibre have been available for some time.

Due to the required real-time communication of industrial controls and critical commands that are time sensitive, ethernet/IP needs surety of delivery. The design of the physical network may employ one or more redundant back-up or alternate pathways. To provide redundancy, actual topologies of the physical cable between switches and devices in the industrial environment may need to be ring, star or bus.

The general requirement for a connector housing is that it meets the IP67 rating to seal against ingress of dust and moisture from humidity or direct contact with liquids. This rating is the highest for dust and second highest for moisture.

The IP protection rating of 6 ensures total protection against dust and the moisture rating of 7 ensures against complete immersion in liquid to one metre.

Resistance to mechanical vibration requires the assembly to maintain optimum interface of plug and jack and ensure no damage occurs to contacts during operation.

Depending on location and mounting facility, the connector interface may be subjected to vibration and physical movement. Continual correct alignment of the plug and jack interface is required plus no shifting of the plug due to vibration.

Expanded temperature ranges will be encountered and materials used in the assembly need to be able to operate in extremes of cold and heat.

The potential for high EMI will exist and the ability to provide shielding of the copper media and connector is a must.

Industrial complexes where high current drawing devices operate, such as injection mould machines, close proximity to RF radiation and welding and electrostatic processes, are candidates for screened copper media. An alternative solution is to install optical fibre that isn't affected by EMI or RFI.

Connector manufacturers have developed RJ45 connector receptacles that are suitable for use in harsh environments where ethernet is to be supported. Designed with one sealing surface on the plug connector interface, the connectors ensure optimum performance even in harsh dust and moisture environments.