Things didnt exactly go swimmingly along the banks of the Tombigbee River at Calvert, Ala., where the ownership of a multi-billion-dollar carbon steel plant built by ThyssenKrupp AG some 40 miles north of Mobile is about to change.
By May 2012, less than two years after the Essen, Germany-based metals, materials, engineering and manufacturing firm opened the doors of the 4.3-million-tonne-per-year plant, ThyssenKrupp (TK) was reviewing strategic options relating to its steel portfolio and the future of the Calvert facility and a sister plant built in Rio de Janeiro to supply slab to the American mill. The company is now entertaining bids for the plant from domestic as well as foreign mills.
For all the reversals, some things went right at Calvert, where a full-court press by Siemens AG and one of its solutions providers untangled one of the more frustratingand costlysnarls in product flow through the facility.
The Calvert plantwhich is equipped with a hot-strip mill, cold-rolling mill, four hot-dip galvanizing lines, a rail yard and a river terminal to access the Port of Mobile and Gulf of Mexicoproduces cold-rolled steel in coils weighing up to 14 tonnes. When in operation, high-speed rail cars moving at speeds up to 33 miles per hour transported the coils through two underground tunnels, each measuring almost 500 feet long, to any of eight separate drop points. The coils were then lifted by crane off the rail cars and into other plant facilities for further processing or shipment to customers in the auto, construction, pipe, tube, and appliance/HVAC industries.
Control of the rail cars was provided by a Siemens Simatic S7-400 process controller communicating by Profibus to remote drives and the I/O aboard each car. The Profibus communication used a microwave rail that runs the full length of each tunnels track. Each rail car was outfitted with a metal paddle that rode a slot in the rail, acting as an antenna for the controllers signal.
Although ThyssenKrupp had implemented a similar approach successfully at locations outside the United States, management found the microwave rail a constant source of costly disruptions in rail service during Calverts first year of operation. What they had failed to take into account, it seems, was the high humidity of southern Alabama.
And climate wasnt the only issue. As it turned out, the alignment required by the microwave guide rail could not be consistently achieved, in part due to vibrations caused by the heavy rail cars movement. Add to that yet another spoiler: dirt and dust kicked up by the movement of the heavy rail cars.
"These disruptions were not only interrupting product flow within the plant, but were also jeopardizing production and shipping schedules," said John Elias, a software engineer with Mobile, Ala.-based Prism Systems Inc., one of the key contractors for the TK project and a Siemens Solution Provider. Prism, which was founded in 1989 and serves a global customer base, specializes in automation and controls as well as industrial software development, data integration and reporting, engineering, consulting and project management.
Confronted with a weak link that needed fixing fast, TK turned to Elias and his colleagues at Prisms Systems Design Group, who soon realized that the problems posed by vibration, dirt and heat made the rail car snafu an ideal application for an industrial-grade wireless local area network (IWLAN) solutionalmost.
Their hesitation hinged on two key concerns. For starters, the tunnel walls at TKs Calvert plant would subject the IWLANs radio signals to shadowing and reflection. "The former could interrupt the wireless communications while the latter could cause radio interference," Elias explained.
"In addition, the IWLAN solution needed real-time communications to keep the Siemens process controller in virtually constant contact with the rail cars on-board remote drives and I/O," he added. The issue here, Elias said, is IWLANs use IEEE 802.11 technology that is optimized for stationary usenot for transmissions involving fast-moving vehicles like rail cars. In fact, even with a central 802.11 access point controller doing a constant background scan of the signal environment, the latency in one access point handing a signal over to another access point can be several seconds, he said.
Looking for an answer on both fronts, the Prism Systems team turned to RCoax, specialized so-called "leaky" cabling supplied by Siemens that could run the length of Calverts tunnels and provide radio signaling without shadows or reflections while dispensing with the problems of vibration, dirt and heat. RCoax cabling features a center rod-shaped antenna sheathed in a dielectric layer of polyethylene, then covered by a layer of reflective copper and protected from moisture and dirt by an outside layer of plastic. "The copper shielding is perforated at regular intervalsmade leakywith each perforation emitting a radio field thats restricted to a single plane," Elias said.
RCoax is available in two versions: 2.4 GHz for wide-area radio coverage and 5GHz for close in (10 cm) radio coverage. Prism Systems opted to install the 5GHz (close-in) version at Calvert.
To solve the latency issue, Prism turned again to Siemens toolbox of offerings and opted to install a Profinet and 802.11 media access control technology, which its developer and sole provider calls an industrial Point Coordination Function (iPCF). Because the iPCF technology reduces the access point handover latency to less than 20 milliseconds, it provides whats called "rapid roaming" or effectively real-time wireless communications, Elias said.
"The need for real-time communications and Siemens iPCF technology is why we chose Siemens Scalance access points, which has it," he noted. "This way we could proxy the Profibus network wirelessly using Profinet and insure no communication breaks or interference as the rail cars move along the tracks."
Before actually engineering the solution, Prism conducted a radio spectrum audit. "Even though RCoax has such a small radio signature, we had to identify all sources of possible interference," Elias explained. So we did a spectrum analysis to learn what other radio channels might exist in the tunnels and around their outdoor openings and then isolate ours using separate channels."
When the engineering was complete, Elias said, implementation was a snap. "All the I/O aboard the rail cars was already using Profinet so after we laid out the RCoax cable and deployed the Scalance access points, we just swapped out a card of each rail cars I/O module. There were no logic changes."
All measures were taken to insure that security was not compromised, he added, noting that the Siemens technology operates in temperatures up to 140 degrees.
Besides eliminating a costly source of delays along TKs production line, the solution devised by Prism Systems is cost-minded. "There are little if any operating costs because theres no wear-and-tear, which saves maintenance and repair costs for items like connectors, cables, sliding contacts or winding devices," Elias said. "Implementation could not have been easier."
"Another vendor proposed an enormously complex and more expensive solution needing all kinds of Profitnet translators and other devices," Elias added. "With Siemens, we were able to provide ThyssenKrupp a much better solution with much greater confidence it would solve their problem."