As the industry advances more and more towards automation, communication networks are becoming an integral part of the functioning of a growing number of companies. Nowadays, the role of man is becoming increasingly limited to the supervision, control and service of automatically operating devices. Tasks imposed on industrial data networks are much more demanding than in the case of standard networks, for example. Industrial networks work on both small and large amounts of data, and their main task is to ensure communication on many levels in a relatively short time. These networks often consist of a large number of network devices that we often don't see, yet they constitute an inseparable part of the entire infrastructure.
How to choose an industrial network cable?
In this article we will focus primarily on cables, their properties and characteristics, but before we move on to the very characteristics of cables, it is necessary to get acquainted with communication networks which are commonly used in manufacturing plants. Everyone who has had contact with them, has also encountered names such as Profinet or Profibus, so let us discuss the characteristics of these networks and how they work.
Profinet cables for industrial networks
The term Profinet is a common abbreviation for Process Field Net and it is nothing else than a communication network based on the Industrial Ethernet standard, i.e. the Industrial Ethernet standard. Profinet supports 256 devices using communication paths such as IRT (isochronous real-time communication), RT (real-time communication) and TCP/IP (Transmission Control Protocol/Internet Protocol). The choice of communication channel is often determined by the future use of the network. The simplest Profinet network model consists of at least one IO Controller, acting as a controller, responsible for data processing, IO-device stations and one IO-device that delivers data to the IO Controller.
Profibus cables for industrial networks
Profibus stands for Process Field Bus and is a real-time network standard that supports 127 devices. Communication is based on the master/slave relationship, where the master decides whether to switch the slave on or off. The principle of operation, although it may seem straightforward, requires precise design of the operation of the devices in specific periods of time. The main task of the network is to effectively send a large number of short messages, minimizing the time needed for their transmission. In general, the Profibus standard can be divided into Profibus PA (Process Automation), Profibus DP (Decentralized Peripheral) and Profibus FMS (Fieldbus Message Specification). A Profibus network uses a fibre optic cable or RS485 interface as a signal transfer component.
Choosing cables for industrial networks
The condition for an industrial network to function properly is not only the selection of the appropriate cabling itself, but also its correct arrangement. It is necessary to remember, among other things, to minimize the impact of electromagnetic interference by maintaining an appropriate, safe distance between feeder cables, power supply cables and Profinet and Profibus network cables, as well as their proper protection. The risk of interruption or mechanical damage to the cables must also be eliminated, e.g. by using a cable route or protective braiding. The selection of appropriate protection of cables and wires is often determined by the environment in which they will work. It is therefore necessary to adjust the protection to the prevailing conditions. In places where the probability of mechanical damage is highest, it is worth using metal ducts or guides. You should not exceed the specified cable length in the given segments and the number of devices connected to the network. It is also important to maintain a minimum bending radius and to avoid tangling and intersecting cables, if possible.
The key parameters when selecting the cables include:
- Operating temperature - technical specifications for cables often include maximum and minimum operating temperature, taking into account cable location and fixed or mobile operating mode. It is worthwhile getting acquainted with the temperatures and take measurements in the workplace before making a selection. Most of the cables available at TME operate in the range from -20 to 70°C.
- Bending radius - it is important to remember not to exceed the maximum bending radius, which leads to damage to the conductor and, consequently, to a permanent interruption of data transmission.
- Insulation material - it is one of the key parameters which determine the properties and resistance of cables. Properly selected outer insulation material will protect the cable against any mechanical damage, chemical substances, atmospheric agents in case of external applications, as well as protect the installation by not spreading the flame. It is worth considering halogen-free materials, which do not contain elements such as chlorine, bromine, iodine or fluorine in their structure, materials which do not emit toxic gases that pose a hazard to humans during fires. The most common outer insulation materials are PUR (polyurethane), PVC (polyvinyl chloride), FRNC (flame retardant non corrosive), LSZH (low smoke zero halogen), which is a material which does not emit harmful gases.
- Cable shield structure - it is a direct protection of the signal against external interferences caused by the proximity of operating devices, other cables, often power supply cables, which affect the quality of the transmitted signal. Both the cables themselves and the conductors twisted in pairs can be shielded. Commonly available shields include copper wire braid, additionally silver plated or tinned, and aluminium foil, which is often additionally reinforced with plastic layer. To increase the effectiveness of protection against electromagnetic interference, it is quite common to use several screens simultaneously.
- Categories of network cables, which determine the bandwidth and speed of data transmission. Each category is characterized by a specific range of these properties. For example: Category 7 copper cables (Cat 7) transfer data across the 1 to 600 MHz band, at speeds up to 10 Gbps, while commonly used Cat 5e cables transfer across the 1 to 100 MHz band at 1 Gbps.
- Other equally important parameters include the number and cross-section of conductors and the outer diameter of the cable, which plays a significant role in tight, inaccessible places. The diameter depends on the aforementioned number and cross-section of conductors, applied shield or outer insulation material.
TME’s offer includes numerous cables dedicated to industrial communication networks. These are the products of such recognized manufacturers as: LappKabel, Helukabel, Harting, Igus or Belden. The cables are parametrised and contain the necessary information to enable comparison and identification.