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.
Notable Constructional Differences
There are several major differences between commercial and industrial cabling.
Inner Conductors. Industrial cabling tends to involve a lower-gauge, thicker cable for the inner conductors. This allows for less electrical resistance and enables a stronger overall connection despite vibrations, shock, or flexure.
Shielding. Twisted-pair cables for indoor industrial applications will nearly always leverage a braided shield, as that provides a higher resistance to electromagnetic interference (EMI) and RF interference (RFI). When braiding does not provide enough coverage, an additional foil layer of shielding can also be leveraged for more EMI/RFI mitigation with 100% coverage — this is particularly helpful for patch cables that are subject to more interference.
Noise sources such as motor brushes, high-powered switches, heaters, and even lightning can cause cabling to carry interference that can subsequently damage the connected sensitive electronic circuitry. This, in combination with mild to severe voltage transients that come with daily power surges, requires a degree of protection. While surge-protective equipment would handle the brunt of overvoltages, it is still important for cables to have an acceptable level of EMC. This way, unpredictable EMI does not slowly chip away at the functionality of equipment.
Jacketing. The jacketing material is a major consideration since typical thermoplastics will crack, melt, or bulge with exposure to harsh chemicals or oil. Thermoplastics such as Teflon or PVC are often leveraged for cable jacketing due to their recyclability — no chemical bonding occurs during the curing process so the material can be remelted and reformed. Additionally, thermoplastics tend to be much easier to strip, allowing for a higher degree of flexibility during the production process. These characteristics, however, make these cables particularly susceptible to heat and abrasions.
Thermosets (e.g. neoprene, EPR), on the other hand, cannot be recycled as easily due to the cross-linking that occurs between the polymer chains during the curing process. This allows the material to generally have far more inherent UV resistance and resistance to high/low temperatures. Cable jacketing subject to temperature extremes, transients, and mechanical stressors would likely not deform with a thermoset material.
Thermoplastic elastomers (TPE) evoke the benefits of both material types with the ability to be remolded while upholding the structural cross-linking in thermosets. In this way, they also maintain a higher tensile strength and durability than the average thermoplastic.
Materials such as polyurethane (PUR) or TPEs are often the ideal candidates for IE installations. PUR, for instance, is a synthetic rubber that can be formulated to resist oils, grease, and chemicals. This is especially important in robotic control applications where oil-based lubricants are often used. When compared to most rubbers, PUR has a higher abrasion/tear resistance and can also be relatively easily molded while also maintaining a high flexibility. It is often noted that thermosets such as neoprene are more flexible than PUR but PUR IE cables can easily have continuous flex ratings that go up to the tens of millions of cycles without performance loss — an important factor, considering cables in automated equipment can be flexed/bent thousands of times daily.
An Underwriter’s Laboratory (UL) rating from the UL-1581 standard listed in Table 1 ensures that the required tests for flammability have been performed for a general-purpose, plenum, or riser application. Figure 2 shows the various flammability ratings. Plenum cables are subject to the most severe qualifications since HVAC spaces can very rapidly spread flame throughout an entire facility with forced airflow. Along the same line, Low Smoke Zero Halogen (LSZH) cables mitigate the release of toxic/acidic smoke that can injure workers.
Connectors. Often, the most critical portion of a cable can be its connector heads. These are frequently the weak points in any installation due to the hazard of potential ingress and unmating due to vibrations/flexure. The traditional RJ45 connector used in Ethernet cables is often not suitable for industrial applications. This is where the circular M12, which was typically used for sensors, was adapted for industrial Ethernet. This is where the various codes for these connector heads become useful. For instance, the M12 X-coded connector contains 8 pins and leverages CAT 6A or CAT 7 copper cables for high-speed Ethernet with up to 10 Gbps of throughput. Table 3 shows some of these codes and their respective use cases.
The M12 connectors are typically at least IP67-rated, which is entirely dust-tight and can resist temporary water immersions. These connectors also feature locking mechanisms that are far more robust than the RJ45 connector with a threaded mate that is not easily unmated or deformed. The overmolding (Figure 3) allows for strain relief at the fulcrum point between the connector head and the cable where bending/flexing can cause the most damage while also providing ingress protection.
In many vision applications, screw-down RJ45 connecters are used in place of standard RJ45 connectors that can become dislodged due to jolting, vibration, gravity, and cable pulls often found in these types of applications. The secure, screw-down mating mechanism is also favored for use in industrial and military applications where exposure to excessive shock and vibration exists.
Each piece and part of an industrial Ethernet cable including the inner conductors, shielding, cable jacketing, and connector heads must be ideally suited to the harsh conditions in industrial environments. The survivability of these cables relies on a slew of parameters that can be summarized in some of the industrial Ethernet standards with the MICE methodology. These requirements lead to specific constructional difference in the cable’s assembly between the typical commercial cable and an industrial Ethernet cable.
This article was written by Dustin Guttadauro, Product Manager at L-com, Infinite Electronics, North Andover, MA. For more information, visit here .