Understanding industrial Ethernet cable requirements
Ethernet plays a major role in passing data through an automation system at high rates. The digital performance of a network is subject to active devices such as switches and controllers. However, passive devices such as cable and connectors ultimately can determine a network’s performance.
A component’s frequency dictates its performance. Cat 5 cables, for example, are specified for operating frequencies up to 100MHz. This cable also is suitable for 100Mbit applications using a two-pair cable and for gigabit (1,000Mbit) applications when using a four-pair cable with the correct connector. It is easy to confuse MHz performance with the Mbit.
Table: Industrial Ethernet cable, frequency requirements
|Class||Frequency range||Data rate||Capability|
Cables of a higher category (class) meet all transmission characteristics of the lower classes and provide an additional performance margin in a given application.
A stranded Ethernet cable does not have the same performance characteristics as a solid conductor. This is important to remember when distance is a factor. Ethernet conductors are typically 26 and 24AWG. It is always best to use the largest size when requiring high data rates over long distance.
The Profinet standard introduced 22AWG cables, which provide significant transmission performance advantage over 26 and 24AWG cables. A full 100 m segment length can be achieved with stranded or solid cable types.
Three types have been defined within the Profinet standard-stationary, flexible, and special application. When using 22AWG cables, selecting the correct RJ45 connector should be done carefully as many are not compatible with the increased wire size and a Profinet cables’ larger outside diameter.
Power over Ethernet (PoE)
Spare conductors in an Ethernet cable can be used to provide power to Ethernet devices. Wire size is important in calculating voltage drop in PoE applications. It is also important to consider cable selection.
The industrial environment requires suitable cables that have far more robust constructions than those used in office environments. Materials such as polyurethane (PUR) are often used to provide mineral oil resistance and high abrasion resistance. They are also halogen-free. Ethernet cables are available with solid conductors, which are only suitable for static applications. Stranded conductors—typically seven strand—are suitable for flexible applications. Highly stranded connectors—typically 19 strands—are suitable for continuous movement applications.
Suzanne Gill, editor, Control Engineering Europe. Lutze Limited provided additional information for this article, which originally appeared in a November 6 Control Engineering Europe article online. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, firstname.lastname@example.org.
www.controleng.com keywords: Ethernet
- Ethernet plays a major role in passing data through an automation system at high rates.
- Passive devices such as cable and connectors can ultimately determine a network’s performance.
- Selecting the correct RJ45 connector when using 22AWG cables should be done carefully because many are not compatible with Profinet cables’ larger outside diameter.
What other considerations should be made when dealing with industrial Ethernet cable requirements?
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