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High tensile strength 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. This is regulated 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 hanging application in the long term.

"In 2011, we replaced an existing purely mechanical lift system at our location in Ludwigshafen," reports Michael Krauß, Head of Construction Organisation at Sparkasse Vorderpfalz. "These are two passenger lifts with a rated load of 650 kg each and a goods lift with a rated load of 1.1 tonnes. The special feature is that the group of three lifts travels in a shared shaft. The lifts serve the entire building. The system is controlled so that some of the floors are only accessible to employees. And if necessary, other floors can be blocked at any time for any period of time. The relevant data is stored online by the lift manufacturer. All it takes is a phone call."

The requirements profile of the savings bank was clear in advance. The existing access control system for 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 not so easy: the lift manufacturer was unable to 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 in the savings bank.

"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 hanging applications from igus® SE & Co. KG, 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.

"Bullet-proof" special cable

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

Tests in the laboratory proved that the special cable in the tensile test performed around 15,000% better than the standard required in the corresponding DIN VDE 0298. When pulled with 2,919N, the cable does not break and data transmission remains permanent. The cable in the system is 74m long.

Due to their own weight, normal bus cables are not permitted as they can only be loaded up to 15 N/mm² due to the lack of a supporting element. All in all, the facts show that the free-hanging cable could be more than 1km long without showing any loss of performance. "For us, this means that we could theoretically extend the building significantly," says the Head of Building Organisation at Sparkasse. To be on the safe side and measure data, an additional cable was initially installed in the lift system. The lifts run with very high frequency. Almost six months after the system was commissioned, the lift had already carried out 56,970 trips. Two years later, it will exceed 160,000 without any faults being recorded. "The approval limit will certainly not be reached - it is more likely that a new lift control system will be installed," says igus Sales Consultant Eugen Kowalczyk with certainty. chainflex® cables for industrial applications are designed for very small bend radii, high numbers of cycles, speeds and accelerations in addition to demanding environmental conditions.

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Mikko Railonvirta

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