Along with the onslaught of Internet of Things (IoT) and wirelessly enabled devices, cloud connectivity has become a major benefit for a range of applications from commercial to military. As of 2018, Ethernet networking surpassed Fieldbus technology in industrial settings (Figure 1). This is partly due to the growth of industrial IoT (IIoT) where the central gateway to all the sensor nodes is necessarily connected to the cloud via a hardwired Ethernet connection. In industrial settings, power over Ethernet (PoE) links can serve cameras for machine vision, to sensors for multi-modal processing capabilities. This article overviews industrial Ethernet, some of its major pain points including networking dynamics, and cable construction specific to industrial applications.
What is Industrial Ethernet?
Industrial Ethernet (IE) is an iteration of Ethernet that was first introduced in the mid-80s and has evolved to support the stringent requirements of industrial environments with critical parameters such as determinism, real-time control, and security. Determinism is an important factor for industrial Ethernet over commercial Ethernet. Traditionally, the Ethernet defined in the IEEE 802.3 standard leveraged random access protocols that were originally ALOHA and then CSMA/CD (Carrier Sense Multiple Access with Collision Detection). These asynchronous protocols inherently lacked the ability to control the transmission and reception of packets, as all stations have equal privileges to exchange any amount of data to any other station at any random time. This leads to the inevitable occurrence of collisions that only increases drastically with network load and therefore the inability to predict the amount of time it takes for a data packet to be received.
The industrial iteration leveraged the platform with protocols that allow the ability to guarantee information can be sent and delivered at specific times. There are a number of industrial Ethernet protocols including Ethernet/IP, PROFINET, EtherCAT, Modbus, and POWERLINK. Generally, all IE models use TCP/IP (Transmission Control Protocol/Internet Protocol) and real-time communication (RT) with bus cycle times that can range from less than a millisecond up to hundreds of milliseconds. This allows for low-latency communications between the PLCs (Programmable Logic Controllers) orchestrating the required motion, relay, and IO control.
Industrial vs Commercial Ethernet: Cable Construction
The critical benefit of industrial Ethernet is the ability to leverage and keep pace with the open Ethernet standard as well as its respective interconnect. There are, however, major differences in the physical cable construction. Industrial automation settings require PLCs and their subsequent interconnect to be able to withstand a degree of vibration, shock, and flexure, among other environmental conditions such as exposure of UV, moisture, oil, and chemicals.
A commercial Ethernet cable is typically equipped with RJ45 connector heads to support the four shielded or unshielded twisted pairs within. The jacketing material would be composed of some kind of cost-effective thermoplastic such as PVC or PTFE (Teflon). The most that would be done to maintain the integrity of the link when the Ethernet cable is bent or flexed is the occasional strain relief boot between the connector head and the cable body. Industrial Ethernet demands much more from a cable physically and, strangely, not as much bandwidth-wise — the average industrial LAN stands at around 100 Mbps. Commercial and residential installations will have to face huge amounts of data-hungry high-resolution video streaming while industrial settings are generally sending automation information. The huge contrast in requirements between these two industries led to many organizations releasing cabling standards specific to industrial settings in the mid-2000s.
Industrial Ethernet cabling standards involve environmental tests such as impact resistance, crush resistance, and water immersion as well as general infrastructure standards. Table 1 is an overview of some of the Ethernet standards. The TR-42 subcommittee within the Telecommunications Industry Association (TIA) released the ANSI/TIA 568 standard through the combined effort of 60 organizations. Within this standard, there are specifications for fiber optic, coaxial cables and, finally, Ethernet cables. The standard specific to Ethernet cables is the ANSI/TIA 568 C.2 standard where the requirements for Cat5e, Cat6, Cat6a, and Cat7 cables are described in detail. This TIA standard is, however, designed for commercial installations and was released to ensure a degree of backward compatibility and longevity of commercial cables; therefore, the specifications listed within this standard cover electrical tests and labeling without including much on harsh mechanical/environmental conditions. The TR-42 taskgroup released the TIA-1005 standard that is specific to cables in the industrial environment. This standard can be seen as a parallel with the International Electrotechnical Commission’s (IEC) 24702 standard and the European EN 50173-3 standard.
One major differentiating factor in industrial-specific standards are their MICE tables (Mechanical, Ingress, Climatic/Chemical, and Electromagnetic compatibility). The specific types of stressors are:
Mechanical: Shock, vibration, crush, impact
Ingress: Particulates and liquid
Climatic: Temperature, humidity, contaminants, radiation
Electromagnetic: Electromagnetic Discharge (ESD), RF Interference (RFI), transients, magnetic field
The MICE method is leveraged to determine the severity of the industrial environment based on these four factors with a numerical subscript next to each letter — the higher the number in the subscript, the more severe the stressor. These standards often reference NEMA or IP ratings, as they are critical in protecting connector heads from various types of ingress. Table 2 depicts the various required parameters in the MICE table and provides a general description for each.