An army travels on its stomach and a coal mine travels on its conveyor belts. Two 500-ft belts, for example, carry high-quality bituminous coal from Jim Walters Resources' (Adger, Ala.) mine No. 3 to a 10-story washer and back to a stacker for shipping.

The mine's old, manual pull-rope system alerted operators to conveyor problems, but couldn't identify exact locations or describe the nature of specific difficulties. This outdated system made monitoring and repairing the two belts difficult and time-consuming. Costly shutdowns lasted hours, even days, while problems were located and corrected.

To eliminate these delays, electrical engineer Tim Burage sought a more efficient monitoring and control system and selected Seriplex Control Bus from Square D Co. (Palatine, Ill.) to provide bit-level network control for the two 500-ft belts. Seriplex is an intelligent, distributed I/O system designed for basic devices, such as sensors, pushbuttons, relays, and actuators. A five-wire Seriplex cable carries signals between a host controller and I/O devices deterministically, faster, and at lower cost per point than a byte-level network, he says.

"Time is critical to our operation because shutdowns cost so much money," says Mr. Burage. "We solved several problems with the Seriplex system, but the most important was reducing downtime. Seriplex's bit-level system sends high-speed signals and works well with the long cable runs we have along the belt lines."

Seriplex components presently connect to both conveyors via a 1,000-ft cable linking 10 I/O points on each belt, including slip switch and pull cord. The network's signal travels at 16-200 kHz for up to 5,000 ft and allows multiple connections to the data line.

Now, when a breakdown occurs, an icon flashes at the control center on the seventh floor of the washer building. The conveyor system shuts down while the location of the problem is identified. Seriplex's internal diagnostic capability allows troubleshooting from the control center. Operators can also bypass the breakdown and restart the conveyors by accessing a maintenance page feature included in the system's operator interface.

Mr. Burage reports the Seriplex system has simplified maintenance and made unnecessary the excess wiring that plagued the old system. He adds that Seriplex also integrated well with mine No. 3's Siemens' TI545 PLC, Paneltec SD3000, and Cutler-Hammer's PanelMate components.

"We had thousands of feet of wiring to handle before using the Seriplex system. It made maintenance a real problem and contributed to extended downtime," says Mr. Burage. "Seriplex's open technology has made it easier to mix and match devices from different manufacturers."

Because of Seriplex's success in the washing building, Mr. Burage adds, Jim Walters' Resources decided to install a similar system underground at mine No. 3. Seriplex cooperates with Siemens' PLCs to control safety lights and other equipment. The mine has more than 25,000 ft of Seriplex data line underground and outside.

"Seriplex demonstrated what we needed: fast, accurate data in a rugged environment," says Mr. Burage. "And you don't get much more rugged than a coal mine."

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