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Case study<br />

Leaky feeder cables provide<br />

non-contact WLAN operation<br />

The Austrian plant manufacturer Berndorf Band produces endless transport and process belts made from<br />

stainless steel. The company has equipped its biggest production hall to date with the latest automation<br />

technology. The production plant makes 3.5mm thick steel bands with a length of up to 270m. Providing<br />

WLAN connectivity for mobile production cells along the length of the hall required a signal field with<br />

<strong>special</strong> properties. Peter Hallas explains.<br />

Long job: The steel belts are almost 300m long and have<br />

to be worked on with movable stations along their length<br />

THE PROCESS and transport belts produced at<br />

Berndorf Band are mainly used in the chemical<br />

industry, food & beverage production and by<br />

producers of timber and laminates. Each band<br />

is produced exactly to customer requirements<br />

from the raw materials which include stainless<br />

steel, carbon steel or titanium. Production<br />

takes place on two lines which simplifies<br />

handling of the band rolls and the individual<br />

processing stations. This makes production<br />

both faster and more flexible.<br />

Communication by radio<br />

In building a new production hall of enormous<br />

dimensions, the company encountered a<br />

challenge in getting power to the individual<br />

PHOTO: SIEMENS A&D<br />

workstation cells. These need to move about<br />

on rails with the actual position of individual<br />

stations determined by the length of the belt<br />

and the processing steps such as welding,<br />

grinding and polishing to be carried out. The<br />

power supply to these stations is provided from<br />

above by loop conductors so that the hall floor<br />

can be kept free of cables and wires, an<br />

essential advantage over the old solution with<br />

cable drag chains.<br />

Communication in the plants takes place via<br />

Profinet and Profibus. This also includes the<br />

entire safety-oriented communication sent<br />

using Profisafe. This data, which includes the<br />

Profisafe layer, has to be sent reliably to the<br />

work stations. To achieve this over the<br />

dimensions of the production required the<br />

installation of a leaky feeder cable, which is<br />

installed under the hall roof together with the<br />

loop conductors for the power supply. This<br />

<strong>special</strong> transmission line cable has deliberate<br />

discontinuities along its entire length. Each<br />

discontinuity acts as an antenna for the<br />

Scalance W access points. The leaky feeder<br />

cable provides a well-defined radio field along<br />

its length and can provide standard two-way<br />

WLAN communication at either 2.4 or 5GHz<br />

with reliability. Using co-located power cables<br />

and feeder, the actual radio path runs to just<br />

a few centimetres into the WLAN interface<br />

components mounted on the movable work<br />

station.<br />

The non-contact data transmission takes<br />

place without wear and is thus maintenancefree,<br />

a major advantage over a wiper contact<br />

application.<br />

The Industrial Ethernet system connects all<br />

the Simatic S7 standard and failsafe CPUs used<br />

in the system within the distributed<br />

automation architecture, as well as the<br />

distributed ET 200 I/O units, each with others,<br />

and with the master WinCC visualization system<br />

and the control panels. Profibus is used locally<br />

within the workstations. There are no differences<br />

between this radio variant and a fixed<br />

wired Profinet communication in the programming<br />

with Step 7 and the connection of the<br />

<strong>wireless</strong> components. An AS-i cable and a link<br />

to the Profibus via a DP/AS-i link reduce the<br />

wiring effort in the band coiling machine. The<br />

system has been running stably since commissioning.<br />

Peter Hallas is with Siemens A&D, Austria<br />

First published in the <strong>industrial</strong> ethernet <strong>book</strong> September<br />

2009<br />

PHOTO: SIEMENS A&D<br />

Loop conductors with co-located leaky feeder provide<br />

data and power to the production line from above<br />

52<br />

<strong>industrial</strong> ethernet <strong>book</strong><br />

sponsored by Advantech

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