In recent years, halogen-free cables have become popular as they offer significant safety advantages and also reduce damage to the environment. As this technology is now more widely used, many industry standards or industrial applications specify halogen-free cables.
Halogen-free cables distinguish themselves as the materials used are free from chlorine, fluorine, bromine and iodine. Fluorine and chlorine are used in plastic molecules such as fluoroplastic or PVC (polyvinylchloride), whereas bromine is used in flame retardants. It is however necessary to understand that halogen-free allows minimum amounts of chlorine and fluorine. A cable is called halogen-free if less than 0.2 % chlorine and less than 0.1 % fluorine are used. Halogen-free materials are classified according to DIN VDE 0472.
In the event of a fire, traditional PVC cables burn with a thick toxic black smoke containing hydrochloric acid. This smoke is dangerous when inhaled, reduces visibility considerably and is corrosive. In contrast, halogen-free cables only give off faint smoke which is less toxic and is not corrosive, significantly reducing the damage to computer storage media such as hard disk drives where data can be destroyed by thick smoke.
While the driving force for halogen-free is primarily safety, cables manufactured without the use of PVC and phthalate (softeners) cause less harm to the environment. The disposal of halogen-free cables also does not cause problems. When the metallic cores have been removed, the plastic can be recycled or disposed of safely.
Halogen-free cables should not be mixed with the term "low smoke zero halogen" (LSZH) or "low smoke free of halogen" (LSOH). Halogenfree defines the behaviour of the cable material in case of fire or the flammability. 'Low smoke' requires that little smoke is produced. 'Zero halogen' requires that no halogen is released and no corrosive or etching acids are released. Low smoke zero halogen is becoming very popular and, in some cases, a requirement where the protection of people and equipment from toxic and corrosive gas is critical, for example in the railway industry.
Due to environmental demands, more and more lubricants, greases and hydraulic fluids are bio-degradable. While gentle on the environment, these bio-oils are aggressive and can cause traditional cable insulation and jacket materials to swell and decompose.
Modified polymers are used in the manufacture of oil-resistant cables. These cables are subjected to extreme testing in order to ensure longlife in applications where oil contamination is likely.
In applications where surfaces are refined, such as in automotive painting or coating plants, it has to be ensured that the cables do not contain any material that can disrupt the paint wetting.
As the maximum application area for standard cameras is in the range of 40 °C to 50 °C, applications above 80 °C are an exception in industrial vision applications. However, it is possible to supply cables in material that extends operation beyond the levels for some cables types such as CAT6 networking cables. For temperature ranges of -40° to +180 °C (and for brief periods up to +250 °C) Teflon cables with PTFE, FEP or PFA isolation can be used. The raw material is also highly resistant to chemicals and detergents and thus frequently used in medical or food applications.
For use in clean room conditions materials that are vacuum baked with a stable surface such as PUR (polyurethane) in connection with nickelplated full metal end caps are used. In addition these cables are produced using lead-free crimping technology without the use of flux material.
Fibre optic cables are used to transmit light over long distances through either glass or plastic strands. The advantage with this method of data transmission is that the distances that can be covered are far greater than with copper cabling. Additionally the data bandwidth is also increased compared to copper and EMC problems do not occur. The only downside when using fibre optics for data is the difficulty of joining or extending them. Generally, fibres used for vision applications will be purchased at the correct length to avoid these problems, and most cables will have ready moulded connectors that allow easy connection to repeaters and extenders.
As with most cabling, care should be taken to source quality products. We stock a wide variety of fibre optic products suitable for all types of industrial and security applications. As fibres are difficult to repair if damaged, we generally recommend additional 100 % spare fibres to be installed in long runs with shorter patch cables at each end where there could be a lot of manipulation. This allows easy reconfiguration if a cable is damaged. While most fibre transmission endpoints utilise LC fibre cables, we recommend joining the patch cable to the long installed cable using a lockable ST style connector.
GigE Vision is probably the most popular machine vision camera interface, and being based on a professional rather than consumer technology we find the widest range of cable options. Other than a choice of connectors, RJ45 (with or without screws) and different IPclass connectors, they are differentiated according to cable category/ transmission class. Vision applications mostly use CAT5e and higher classes. We recommend the use of high-grade CAT6 cables wherever possible and even offer a robotic rated CAT6 cable. For drag chain applications or applications in harsh environments it might however be necessary to use CAT5e cables due to lack of suitable materials.
CAT5e: CAT5e cables are used for signal transmission with high data transfer rates and are designed for operating frequencies of up to 100 MHz. Cables consist of four wires in twisted pairs, enabling data transmission of up to 1 GBit.
CAT6 / CAT6a: These cables are the standard used for machine vision applications. CAT6 cables can be used for frequencies up to 250 MHz, whereas CAT6a cables can be used up to 500 MHz, fulfilling the bandwidth requirements of 10-Gigabit-Ethernet.
As a rule the maximum permissible length of the transmission distance is 100 m. This distance includes 90 metres line length, plus two times 5 metres patch cable and two connectors. Practice however has shown, that not all cables available on the market work perfectly over such long distances. The use of a switch is therefore highly recommended for cable lengths approaching 100 m.
In addition to the CAT classification of an ethernet cable, the level of shielding also affects the performance of the cable in industrial environments with significant electrical noise. Shielding can basically be divided into braided shielding and foil shielding. Braided shielding is mainly used for applications with linear movements (drag chains), whereas foil shielding is used for robotic applications due to its good torsion properties.
In Europe the wire of a cable does have a definition in square mm, but very often the cable cross section is defined by American Wire Gauge (AWG). The following table compares both definitions.
AWG (American Wire Gauge):
|AWG||Copper resistance (Ω/km)||Metric equivalents (mm²)|