Auxiliary Equipment: Networking: behind the scenes

You’ve probably heard the terms tossed around: Ethernet, DeviceNet, Modbus, fieldbus. These are the behind-the-scenes tools that enable you to monitor and control multiple blenders from a common control panel, or have your materials supplier monitor silo inventory, or have your downstream cooling tanks controlled from the extruder’s operator panel.

Materials handling equipment, including silos, hoppers and bins, vacuum and pressure pumps, conveyors and blenders, can be integrated into a plant-wide inventory control system with the addition of intelligent communications, explains Tony Lawson, director of engineering with Foremost Machine Builders Inc.

This communication can be as simple as discrete I/O switching to indicate status or more advanced communications using any number of commercial protocols as a means to exchange more detailed information and commands.

All of Foremost’s control systems are PLC-based, says Lawson, providing an open architecture that allows flexibility when the company is asked to interface with any other process equipment suppliers. He believes every auxiliary equipment supplier must have this flexibility or be at risk of losing bids based on incompatibility with the main process equipment supplier’s control system.

While interoperability between almost all networking tools is possible, processors would be wise to learn the basics of networking and inter-device communications so that current equipment purchases are optimized for future process control and data acquisition needs, instead of becoming a bottleneck.

The current trend in auxiliary equipment for plastics processing is to provide interface modules for the common fieldbuses. Fieldbuses are a special form of network dedicated to data acquisition and the control of sensors and actuators. The most common industrial fieldbuses are CANopen, DeviceNet, Foundation fieldbus, Interbus, Modbus, and Profibus.

“Process Control Corp. began several years ago to implement new interfaces and communication protocols such as Ethernet, DeviceNet, Profibus and Modbus,” explains Amy Chason, marketing coordinator for Process Control Corp., a manufacturer of auxiliary equipment.

“The future for Process Control’s manufacturing automation software,” she adds, “is moving rapidly toward the introduction of Ethernet/IP and Modbus/TCP capabilities.”

Ethernet hits the plant floor

“Ethernet is becoming more and more prevalent in the industrial setting. I believe much of its growth has to do with the communications networks in the office — many users expect to see that level of communications between PLCs,” says Ron Tump, manager, controls engineering with Schenck AccuRate.

In recent years, various industrial versions of Ethernet have been developed — such as Ethernet/IP, Interbus, Profinet, IDA, Modbus TCP/IP — that will permit industrial Ethernet to expand from its communication function into the process control realm.

“At Conair, we’re seeing some instances of industrial Ethernet in plastics plants, but adoption is moving slowly,” reports Mark Ollander product manager, controls for Conair. “What we are seeing now is DeviceNet, Modbus and Profibus adopted as the “Big 3″. Much of our auxiliary equipment, including central conveying and central water systems, supports these protocols. Future products will support Ethernet as well.”

The end result: integration

Nucon Wittmann Inc. engineered and supplied a massive materials handling system for a U.S. automotive parts molder that used Ethernet as the communications channel between PC-based stations, and Siemens AS-i fieldbus modules combined with Allen-Bradley PLCs for process control.

“We use only off-the-shelf PLCs for our materials handling equipment,” says Rob Miller, president, Nucon Wittmann Inc. “Proprietary PLCs would just make it more difficult to “talk” with other components, such as material level monitoring equipment.”

The project for Cherry Automotive in Waukegan, IL, transformed a production floor littered with gaylords, dryers and vacuum loaders into a streamlined materials handling system. The plant has 53 injection molding machines and handles a large variety of raw materials.

Under the new system, the bar code on bags or gaylords of incoming material is scanned and transmitted to a main database, explains Miller. The material is then conveyed to one of 76 storage receivers in an area removed from the production floor. From the storage bins the material is conveyed to one of 31 drying hoppers or directly to a molding machine. Each injection molding machine has a minimal inventory Clear Tube vacuum receiver assembly at the machine throat.

From the central PC-based control panel, the operator can, among other things, view machine loader status, setpoints, I/O status and alarm history, and initiate transfers between storage, drying and loading equipment, says Miller.

The customized control system is valued at approximately US$250,000.

While the average Canadian plant is not likely to require such an extensive system, the backbone of network interoperability is necessary whether for five machines or fifty.

Thomas Garus of Hamilton Avtec notes that customers are starting to show an interest in having network communications capability on Hamilton Avtec’s standard materials handling equipment. “Our experience to date is that only larger plants with an infrastructure already in place would use this capability, but the interest is there. Everybody is asking questions about it.”

Standard protocols readily available

The trend to standard industrial protocols is evident in all auxiliary equipment, from level sensors in silos to the machine-mounted loader.

Maguire has introduced an adapter module for its Weigh Scale Blenders that will allow the blenders to communicate with other equipment in the plant using the three most widely used fieldbus protocols in plant management systems: Profibus DP, DeviceNet and Modbus. The Maguire Fieldbus Interface (MFI) enables processors to draw batch-by-batch materials consumption data from the blender for plant-wide control in an extrusion or molding plant.

AEC/Whitlock’s VTC7/50D Plus conveying control incorporates Allen-Bradley PLCs and ArmorBlock distributed I/O components with KwikLink flat wiring for an off-the-shelf DeviceNet-compatible equipment network.

Capabilities of the VTC7/50D Plus system include time- or volume-fill loading, local station on/off control, low-level input, alarm output, and local or central proportioning control.

Similarly, Conair offers a “flat-media” distributed I/O loading control system called the DLC48. Using Allen-Bradley ArmorBlock I/O modules connected via KwikLink flat DeviceNet cable, the DLC48 greatly simplifies installation. Up to 48 loaders and eight vacuum pumps (plus a standby pump) can be accommodated. ArmorBlock I/O modules simply clamp onto the DeviceNet cable and then loaders and other devices are wired in via a Universal Terminal Box (UTB) that is standard on all Conair material handling equipment.

Novatec expects the Siemens S7-224 PLC with touch panel to become the primary controller of choice on its dryers. Branded as the NovaTouch PLC, it has an easy-to-read touch panel that measures 14.5 cm (5.7 in) diagonally. Modbus, Profibus MPI, Ethernet, DeviceNet or Canbus communication protocols can be added to enable networking and remote control. The NovaTouch PLC controller is also available for Novatec’s conveying systems.

For processors expecting considerable growth in their operations, Novatec also offers the Exxpand control system. Exxpand uses a distributed control network with intelligent node devices.

Another materials handling system designed for easy expansion is the Ready system from Dega. Ready single-phase hopper loaders can be easily converted to loaders for use in a centralized conveying system by replacing the single-phase suction unit. The replacement head is equipped with a vacuum valve. Once the loaders are connected to the central control via twisted pair wiring, they become part of the central conveying system.

The EXT f
rom Process Control Corp. is a color, touchscreen operator station designed for use on the company’s Gravitrol and gravimetric blending systems. EXT uses its 10BT Ethernet network interface to communicate with Process Control’s PCCWeb embedded web server. It supports various protocols, such as Profibus, EPCC, Modbus and Allen Bradley DH+. These interfaces allow the equipment to be controlled and monitored from additional supervisory systems.

Process Control’s PCCWeb is web-based equipment control system that uses web servers and Ethernet ports built into the operator panel.

Mould-tek has chosen not to pursue the fieldbus mentality, opting for microprocessor control of its blending and conveying systems. “We found it cost-prohibitive to achieve what our customers want through PLCs and fieldbus,” explains Brian Da Silva, vice-president, research and development. Mould-tek’s T-COM2 software was developed exclusively for the company’s GXB blenders with Series 4 controls. The Windows-based software provides two-way communication between a central PC and the touch-screen controls of the GXB blenders. It is suitable for real-time monitoring, maintaining formulas, cycle and inventory reports, building formulas and downloading formulas.