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Tensile special bus cable for chip card readers in a lift system

Eleven floors and the basement area are served by a group of lifts in a Sparkasse building. Not all floors are accessible to customers. They are controlled by an access control system. The required bus signals are transmitted via a special cable which, due to its design, can demonstrably withstand the high tensile strain caused by the freely suspended application in the long term.

"In 2011, we replaced an existing purely mechanical lift system at our site in Ludwigshafen," reports Michael Krauß, Head of Building Organisation at Sparkasse Vorderpfalz. "There are two passenger lifts with a nominal load of 650kg each and one goods lift with a nominal load of 1.1t. The special feature is that the group of three travels in one shaft. The lifts open up the whole house. The system is controlled in such a way that some of the floors are only accessible to employees. And if necessary, further floors can be closed off at any moment for any period of time. The relevant data is stored online by the lift manufacturer. One phone call is enough."

The requirement profile of the Sparkasse was clear right from the start. The existing access control system for the employees, which consists of card readers, was to be transferred to the lifts so that access to the bank and operation of the lifts would work via the existing chip card. However, the technical implementation turned out to be tricky: The elevator manufacturer could not offer a bus cable that would have made it possible to connect the existing card readers. The solution came from the electrical installation company Keipp from Ludwigshafen, which carries out a wide range of electrical and installation work for the Sparkasse.

"Our contact person suggested that we use an extremely robust bus cable for long, suspended travels from the industrial environment," recalls Krauß. "At the time, however, it was still in the test phase. Nevertheless, we decided to use it. And we haven't regretted that decision once."

Technical advantages of special cables

A chainflex® special cable CFSPECIAL182.045 for suspended applications from igus® GmbH, Cologne, has been installed in the lift system, which fulfils all applicable standards and guidelines and far exceeds them in terms of tensile strength. The CFSPECIAL series introduced in 2012 supplements the standard product range with cables for very demanding applications. This series also includes special cables, for example for the railway sector or cables with high tensile strength.
There are a number of reasons that speak in favour of special cables. They offer solutions for applications that go beyond normal energy supply applications. The growing product range of special cables is based on the requirements of customers from all sectors, for which suitable solutions are developed and tested.

"We manufacture cables for almost every application, using a wide variety of materials and processes," explains igus® Product Manager Andreas Muckes. "Depending on the design, this is possible from lengths of 500m." A wide variety of cables are tested in the company's own laboratory, particularly with regard to their dynamics over long and short distances. Radii and torsion also play an important role. The focus is always on the right cable concept for demanding movements. Over 2 billion test cycles are realised every year for research and development.

"Bulletproof" special cable

The special cable for data transmission in the lift system hangs freely in the shaft and easily absorbs the weight forces that occur. It has the same four-pair core structure as a normal Ethernet cable, a TPE inner jacket and an extremely rigid braided shield. The difference to standard bus cables lies in their jacket structure. The black outer jacket is made of a low-adhesion, highly abrasion-resistant PUR compound with an embedded aramid Kevlar fibre. "The material is similar to that of a bulletproof vest," says Muckes. The technical structure sounds simple, but it is extremely sophisticated: The special fibre is braided over a thin jacket. It sinks into the material during the subsequent production of the outer jacket and permanently absorbs all external forces.

In the test laboratory it could be proven that the special cable is around 15,000% above the standard required in the corresponding DIN VDE 0298 in the tensile test. Pulled with 2,919N, the cable is not torn off and the data transmission remains uninterrupted. The cable length in the system amounts to 74m.

Due to their weight and the lack of a supporting element, normal bus cables cannot be used as they only withstand loads of up to 15N/mm². All in all, the facts show that the cable length could be more than 1km free-hanging without any loss of performance. "For us, this means that we could theoretically extend the building significantly," says the Head of Building Organisation at Sparkasse. An additional cable was initially installed in the lift system to be on the safe side and to be able to carry out measurements of the occurring data set. The frequency of the lifts is very high. Just under six months after the system was commissioned, 56,970 trips had already been recorded. Two years later, they exceeded the 160,000 mark without any faults being recorded. "The approval limit will certainly not be reached; it's more likely for a new lift control system to be installed," so igus® Sales Consultant Eugen Kowalczyk. chainflex® cables for industrial applications are designed for very small bend radii, high numbers of cycles, speeds, accelerations and demanding environmental conditions.

Error-free data transmission

This particularly durable special cable with aramid fibre was initially developed for storage and retrieval units that are used in high-bay warehouses that are up to 100m high. At this height, standard cables can have problems with data transmission. These special cables are also proving their efficiency in moving camera systems in forklift applications, where a camera is integrated into the forks and the cable runs over drums. What all applications have in common is that data transmission functions without problems and the safety aspect plays a very important role. In addition, there must be no standstill. "The lift simply has to work. In the interests of reliable customer transport, it must not come to an unscheduled standstill," says the Head of Building Organisation at Sparkasse.

This cable is a customised solution that has been developed to meet the highest requirements. However, all our experience is incorporated into the wide range of chainflex® standard products. This means that the customer is always on the safe side and gets the right cable for every requirement profile.

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Overview of chainflex® applications