Automation is continuing to increase on the factory floor, creating a growing need for more data exchange over sophisticated, high-performance networks. These new developments, known conceptually as the Internet of Things (IoT), are placing new demands on Ethernet cables, which are the backbone of the smart factory environment. These system specific cables must be able to hold their own in harsh factory environments while still supporting high data rates.
Because it can be a challenge to combine the design requirements of robustness, flexibility and high data rates all in one cable, it’s important to know what your options are when selecting data cables for your factory.
Robust factory construction
In many ways, data cables need to be constructed the same way as other industrial cabling, ensuring they can withstand the harsh environment of the factory floor. Ethernet cables in plant-floor equipment must be able to tolerate a wider range of vibration and electrical noise than equipment installed in offices or information-technology areas, for example. The cables must also be oil resistant, withstand high temperatures and function reliably and durably in a cable track.
These requirements lend themselves to certain design considerations, which are universal to all cables:
Cable jacketing: Cables with jacketing made from thermoplastic elastomer (TPE) or polyvinyl chloride (PVC), for example, will be resistant to oil and chemicals. For increased mechanical and chemical resistance, also consider cables with robust polyurethane (PUR) outer jackets. PVC and TPE jackets are ideally suited for applications, such as food and beverage, that require strict compliance with hygienic standards. Bacteria and other microbes can feed on a cable’s polymeric components, causing contamination and degradation of the cable’s insulation.
Shielding: Shielded cables are necessary to have on the factory floor, where there is generally a high concentration of power and power/control cables in one contained environment. Most industrial Ethernet cables have foil and/or copper braid shields, which are constructed by crossing layers of individual copper strands. Braid shields provide both structural integrity and room for flexibility––a necessary balancing act, especially in applications where data cables are exposed to stress or torsion. Some industrial Ethernet cables, such as the ETHERLINE® Cat.7 cables, have individually foil-shielded pairs to ensure transmission reliability in environments with high electromagnetic interference.
Bend radii: The smaller the bend radius, the more a cable can be bent without inducing damage. Minimum bend radii will be dependent on the type of cable being used and the application style of the cable’s installation. For example, a continuous flexing cable used in a continuous flexing application where cables are rolling back and forth in a linear motion will have a larger bend radius than if it was being used in a stationary application. This is due to the significantly higher amount of stress in the former over the latter.
A flexible edge
The importance of bend radii in cabling lends itself to a larger discussion of data cable flexibility––and how a data cable should be constructed based on if and how a machine moves. When a cable is designed for a special flexing application, it has to be manufactured on a unique cabling machine that minimizes the back-twist on the cable conductors. Types of cable motion include:
Continuous flex - The cable is rolling or flexing back and forth in a linear motion. These cables are typically used in cable track applications.
Torsional flex - The cable is being twisted clockwise and counterclockwise with angles varying from 90 to 360 degrees. This type of flexing usually occurs on robotic equipment that is constantly being twisted or flexed for long periods of time.
Bending flex - Known as a “tick tock” motion, the cable is being flexed back and forth while one end remains stationary. The majority of the stress on the cable is on the two focal points where the bend and load are being applied.
In terms of their construction, continous flexing and torsion cables can have fine stranding up to 19 wires, allowing for greater flexibility. They also undergo rigorous testing to ensure they can survive the demands of harsh industrial environments. The ETHERLINE® TORSION Cat.7 cable, for example, is suitable for high-torsion stress and is tested with up to 5 million bending cycles, as well as a right/left movement of 180 degrees per meter.
Demands for higher data
Industrial Ethernet cables must be able to balance robust jacketing and high flexibility without compromising demands for high data rates. The ETHERLINE® Cat.7 series of cabling is ideal for EtherCAT and EtherNet/IP applications that require data rates up to 10 Gbit/s, such as wiring machines and control cabinets. The cable’s robust PUR outer jacket is highly resistant to mineral oils and abrasion, and its double-shielding ensures transmission reliability in factories that have a lot of electrical noise. Because of its small cable diameter and bend radius (4 x the outer diameter in a fixed installation), this cable lends itself to industrial environments that have limited space.
In terms of data rate capabilities, compare Cat.7 cables to other industrial cables on the market (see “Transmission Comparison Chart”). Currently, engineers are moving away from Cat.5e cables, which have a transmission rate of up to 100 MHz, to the currently popular Cat.6A cables, which can transmit up to 500 MHz. Over time, the need for industrial cabling with higher data rates will continue to climb.
The article is reproduced with courtesy to Lapp Group