Happier Together: Process Meets Discrete Networking

Process and Discrete Applications and Their Traditionally Distinct Networks Come Together With the Help of Distributed Intelligence, Ethernet and Related Tools

By Jim Montague

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Just as smaller, slower streams eventually carve out larger, faster rivers, industrial networking evolved from separate methods for individual purposes to common pathways that can handle many different tasks.

Analog signals and data that used to be brought in by point-to-point wires, cables, connectors and cabinets have given way to digital fieldbuses, Ethernet, wireless and Internet-enabled networks that jointly manage data from multiple applications. Power, temperature, vibration, pressure, flow, speed and other traditional values continue to be generated at more varied sources than ever before, but they're more quickly converted into digital formats that can be sent via common networks to controllers and enterprise levels for quicker analysis and better decision making.

In short, microprocessors and software don't care what kind of ones and zeros they chew on, and this brings together process, discrete, motion, power and other functions that used to require dedicated communications and networks.

For instance, W. Müller in Troisdorf, Germany, builds extrusion heads and platforms for retrofitting onto blow molding machines, which are producing more complex and capable bottles and other products with multilayered walls. Müller's CoEx extrusion head works with six extruders to produce a three- to seven-layer, co-extruded plastic strand, which combines a glossy exterior, layer-coupling agents and inner layers that protect consumer products from oxygen or UV radiation and extend their shelf lives.

Because it requires open, flexible controls to integrate new heads onto existing and new machines, Müller switched to EtherCAT networking and TwinCAT software from Beckhoff Automation (www.beckhoff.com). These enable the control-cabinet and other IPCs with dual-core processors to control the extruders' heating zones and wall thicknesses at the same time. Over the sub-distributions of EtherCAT's terminal system, signals provided by the blow-molding machine are logged along with servo-axis motion data and heating zone process-variable information. Generally, one servo axis is used per extrusion machine, and a further axis is used for wall thickness control.

"I/O data comes from the thermocouples" explains James Birt, Müller's control technologist. "Our concept uses a large number of individual heaters, since this is the best way to control the flow of material. A maximum of 220 heating zones are available in the control system, although 50 heating zones are usually sufficient, even for larger systems. There also are numerous temperature-controlled zones for water-cooled feed zones or valve control. The openness and flexibility of this control technology and networking enables us to integrate existing machine signals and drive technology along with temperature controls from third-party suppliers without great expense, and it helps us meet customer requirements for various bus systems."

Batch Principles Aid Instruments

Similarly, Amtex decided in 2010 to automate one of the five reactors at its functional polymers plant in Medellín, Columbia, so it could operate using improved batch methods, follow ISA-S88 standards, move from traditional supervisory batch management to production-based management, and aim to achieve about a 30% production increase. The firm worked with system integrator Automatización S.A. (www.automatizacion.com.co), and together they implemented the first batch application of ABB's System 800xA distributed control system (DCS) in Columbia (Figure 1).

Amtex is Latin America's largest producer of sodium carboxymethylcelullose (CMC), and its four plants in Mexico, Columbia and Argentina have an installed capacity of 32,000 metric tons per year. Marketed under Amtex's Gelycel brand name, CMC is an anionic polymer derived from cellulose that's used as a thickener in the food, pharmaceuticals and oil industries. Amtex has two plants in Columbia, one annually produces 15,000 metric tons of CMC, and the other produces 14,000 metric tons per year of functional polymers.

Consequently, Amtex and Automatización outfitted the reactor with System 800xA Batch Management, which is ISA-S88-compliant, recipe-management, procedural-control software for configuring, scheduling and managing batch operations. The batch software was implemented in conjunction with the reactor's two AC800M controllers, network controls and AC800M connectivity server, which covers 600 tags. The first controller performs process control, while the second is for auxiliary equipment and includes connecting plant meters via a Modbus RTU network to prevent possible data traffic overloads on the process controllers.

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