Is cable 'just cable', or is there more to linking systems than meets the eye?

4 min read

Despite all the focus on the leading edge technologies involved in electronics products of all descriptions, almost all will depend upon an apparently humble component – cable.

For some devices – MP3 players, for example – the cable may be the element which links the intelligence to the user. In others, it may be the means by which data is sent to and received from a hard disk drive. Others still rely on cable to link the various boards in the system. And in many systems, cable brings power from an external source. Whichever way you look at it, cable is an important part of the electronics industry. Yet it's a technology which seems to be very much taken for granted. While fpgas might ride the coat tails of Moore's Law and capture the interest of many engineers, cable is cable is cable. Or is it? Adrian Hyner, European sales manager, systems and components, for 3M says there have been a number of changes in cables over the last 10 years or so. "There have been a range of developments," he noted. "Cable manufacturers have had to cope with higher data rates, which have increased from Mbit/s to 20Gbit/s, while legislation has required them to develop new products by eliminating toxic substances from casings. Overall, the demand has been for cable to become thinner, lighter and more flexible." Habia Cable is a Swedish based manufacturer of specialised cables. Brian Dempster, UK business development manager, said the company is focused more towards designing what people want than making a product and selling it. "People need specific cable for specific tasks," he claimed. An example is Habia Cable's Flexiform range. Development of Flexiform began in the late 1990s, when the telecom industry was looking for a reliable and easy to use coaxial cable for mobile phone basestation applications. "The development resulted in the high performance, conformable Flexiform cable." Dempster simplified the problem: "People are doing things with 'electric string'. They are connecting clever boxes together and the environment and the nature of the signal being sent define how clever the string." Dempster said that, over the last decade, there has been a migration towards 'internet type' signals, rather than discrete communications. "There is a move towards running things over Ethernet and that has some implications for interconnect," he noted. "Cat 5 cable is simple and cheap, which is fine for linking your printer to your computer. Industrialising that cable poses some challenges. Getting IP style cabling to work in an industrial environment means the cable has to be ruggedised." Cable, in Dempster's opinion, isn't just cable. "Habia sells a lot of cable to companies developing products which measure vibration, temperature, noise and so on. From a technical perspective, the cable is integral to the product and the product won't work if the cable doesn't work properly." Habia's UK customers typically include those looking to measure things in hostile environments, as well as those building to military specs. He gave the example of one particular customer, who makes metrology equipment. "Their products sell at a high price," he noted. "The devices include an expensive read head, but there can be as much value in the cable as in the read head. If they don't specify the correct 'bit of string', it reflects badly on them." Earlier in 2013, Habia Cable introduced Habiasense, responding to increased demands for greater flexibility, performance and safety in measurement and temperature sensing applications. Among the advantages claimed for the cable range is smaller size and lighter weight, which is said to make the cables easier to install. The company adds that the cables can be customised for a broad spectrum of applications and industrial environments. Martin Sears, vice president of Habia Cable's industrial business unit, said: "Measurement and sensing technologies are changing fast in order to meet stricter EU demands for accuracy and safety in industrial processes. This means that our customers need to keep pace. "Habiasense cables score highly because not only do they represent the latest technology and meet the most stringent international standards, they also come with a high degree of flexibility and adaptability. This enables us to also provide our customers with custom designed cable solutions." There are four Habiasense cable types – HT1, HT2, ZH1 and ZH2. HT1 cables can operate at extremes of temperature – from -200 to 260°C – while the low smoke, zero halogen and flame retardant ZH1 cable is designed for use in public places or in vehicles, and well as in hot environments. Hyner picked up on one of these elements. "Safety in fire conditions has been a key driver for materials changes. We've seen the traditional pvc conductor coatings being replaced by polyolifin and foil." A recent innovation from 3M is its SL8800 series, aimed at high data rate applications which require the cable to make sharp turns and, in some instances, to fold. According to 3M, the cable offers good bend radius, signal integrity and overall routability performance, allowing it to fit through narrow openings and to free space in tightly packed systems. The SL8800 series features a longitudinal shielded construction, providing resonance free attenuation at frequencies of up to 20GHz and supporting data rates of 25Gbit/s and beyond. Dempster picked up on the safety angle. "Cat 5/6/7 cables are good electrically, but don't have good temperature and fire resistance. That means we have to bundle it with other things in order to protect it and packaging has now become an interesting aspect. "Say, for example, you wanted to run an IP cable around the London Underground system. The cable has to conform to given standards and that's hard with polyethylene because it burns like a candle and it smokes. While you can improve the electrical performance, you still have a problem. In order to meet those requirements, you may have to specify a cable with multiple levels of heat shielding." He added that the military market had equally strict requirements. "In military rf applications, for example, there has been a desire for the interconnect to carry more power. That's particularly relevant to jamming systems. And there are other harsh environments." Asked what his customers were looking for when they specified cables, Hyner said: "Fitness for purpose and value for money. There's no point in buying a high performance flat twinax when a traditional ribbon cable will serve equally well. But, when data rates and transmission distances increase, signal integrity becomes a serious issue and it is then that cable reliability becomes key. "In many ways, cable is now commoditised, but there is still the need to choose carefully in some applications above and beyond cost." Dempster concluded: "Ask yourself what you need from your interconnect. Do you buy something off the shelf or do you specify something that is tailored to a particular product? The correct cable depends on the environment, the signals being carried and how critical it is that an accurate signal arrives at the other end. But if you're putting an unshielded cable into a noisy emc environment, the results won't be good."