A premiere manufacturer of artists' coated canvas needed to update the control equipment on its coating line and drying oven. The coating line runs 40,000 yards of canvas per day in a 300,000 sq ft facility. The existing coating line and drying oven had been in operation for nearly 25 years and all control and monitoring was carried out through hardwiring and relay logic.

The maintenance manager faced a difficult problem. While the coating line was mechanically sound, the drying oven had to be replaced. The new drying oven was purchased with an Allen-Bradley SLC 5/04 controller, so the controls for the drying oven had to be integrated into the coating line.

At that point, an exact I/O count could not be determined and the precise location of sensor and operator stations was not known. To make matters worse, only a two-week downtime could be allotted for removing the old drying oven, installing the new oven, and updating the controls. The manufacturer required a wiring system that would be easily expandable, offer a simple PLC connection, allow maximum flexibility, and be simple enough to have the installation running in a very short period.

Numerous industrial networks were considered, but stumbling blocks were encountered with each. One problem is that most networks have a steep learning curve unsuitable for time-critical applications. Another is that many bus systems need specific configuration software requiring a key disk for operation. Losing or deleting a software's activation during routine maintenance or troubleshooting can result in hours of downtime. Training maintenance technicians and other personnel on a new software package is also expensive. Additionally, other networks are limited in cabling topologies, making I/O module placement inflexible and difficult.

The AS-Interface Solution

"About that time, a unique, trapezoidal-shaped, yellow cable was shown to me by my local supplier. He claimed to be able to connect over 240 I/O on this two-conductor cable," remarked the maintenance manager. This wiring system, known as the Actuator Sensor Interface or AS-Interface, connects up to 31 nodes, each capable of four inputs and four outputs, for a total of 248 I/O per system. The system is completely deterministic, with a cycle time of 5 ms for a fully loaded system.

Power and communications share the same two-conductor, unshielded round, or AS-Interface flat cable. Any cable topology is supported, network termination is not required, and cable runs up to 328 ft are possible. For longer runs, repeaters can be used to extend the cable length to a maximum of 990 ft.

"A direct SLC 500 AS-Interface master was available for my PLC, and it did not require any additional software for configuration," the maintenance manager added. "I simply needed to address the modules and connect them to the cable. All functions and setup were accomplished using the SLC 500 ladder editor."

The AS-Interface solution made sense, but questions remained to be answered. Is there an installed base and engineering support in the U.S.? Is it possible to pull off an installation of this size in two weeks? How can the manufacturer choose an AS-Interface product supplier from the hundreds available?

Finding Local Support

Developed in 1990 by a consortium of 11 manufacturers, AS-Interface has a worldwide installed base of over 2 million slave modules. After initial development, the consortium opened the specifications to any interested manufacturer. At present, there are over 200 manufacturers of AS-Interface products. Released to the U.S. market in 1995, AS-Interface has been on a rapid growth rate with success stories in many types of applications in both process and factory automation. AS-Interface is standardized, and compatibility is ensured, because each product is conformance tested by an independent test lab.

Pepperl+Fuchs offers a wide selection of I/O modules, masters, power supplies, and accessories, and as one of the 11 original members of the development consortium, has experience in all aspects of AS-Interface. Pepperl+Fuchs has engineering, development, production, product management, and sales support in its U.S. headquarters located in Twinsburg, OH.

"Support from Pepperl+Fuchs was key to my decision to select AS-Interface for the new coating control system," added the maintenance manager. "The engineering support staff was terrific in helping me get this system up and running in short order."

AS-Interface is extremely simple from the programming side, because the master is completely transparent. The I/O data is directly mapped into memory so it is identical to what the user would see using a conventionally wired system with standard I/O cards. When the manufacturer compared the material cost of AS-Interface to conventional wiring, AS-Interface was slightly more expensive. During installation, however, labor costs were cut by almost 75%. An installation of this size would normally take two weeks of design time plus an additional two weeks pulling wire. The design and wire pulling times were cut down to about two days each. The installation was trouble-free and completed well within the two-week timeframe.

"Typical cost savings reported by our customers when considering all factors of material and labor cost averages about 40%," stated Gary Frigyes, product manager at Pepperl+Fuchs, Inc.

The coating line has been in operation for two 10 hr shifts daily for the past 14 months. The strengths of AS-Interface are becoming increasingly apparent the longer the system is installed.

"We were adding a lot of new technology to the plant during this two-week window, including touchscreens, Profibus, and other systems; AS-Interface was by far the easiest to install. We have been able to add additional I/O or move existing I/O modules in about two hours. The diagnostics and LEDs on the I/O modules have even enabled me to troubleshoot the coating line over the phone with one of my line supervisors on the shop floor. Our maintenance technicians are requesting AS-Interface to be used in other locations for monitoring, data collection, and control, and we are adding two more AS-Interface systems this year," concludes the maintenance manager.