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With Wide Array of Fieldbuses, Manufacturers Can Choose Automation System(s) Independent of Motor Drives

(Technology to Make Drives and Systems Compatible Increasingly is Built Directly Into Drives, or Easy as a Snap-on Module with Simple Two-wire Twisted-Cable Hook Up)

NEW BERLIN, Wis., March, 2003 . . . Demand for fieldbus technology, which allows AC drives to be networked with controllers to provide real-time, precise motor control from centralized automation systems, continues to grow rapidly and, increasingly, the technology is either being built into drives directly, or as snap-on modules, so that drive and fieldbus are virtually seamless, according to Steve Weingarth, application engineering manager for ABB Inc., Automation Technologies, Drives, Motors & Machines.
Weingarth offers this quick primer regarding fieldbuses:

What is Fieldbus?
Fieldbus is a fully digital and duplex data transmission system that connects intelligent field devices and automation systems to an industrial plants network. Unlike point-to-point connections, which allow only two circuits to exchange data, fieldbuses usually join a larger number of circuits, each of which take an active role in the exchange.

A fieldbus transfers information sequentially (serial, one after the other) and is often referred to as serial communications.
Fieldbus topology differs from point-to-point, offering higher installation flexibility, as the technology makes it very easy to add a new circuit to the existing system. However, because there is not a standardized protocol for different devices to communicate with automation systems, the number of fieldbuses continues to be varied and proliferate.

A device on a system (such as a motor drive) is usually described as a node. Globally, there are many hundreds of thousands of "nodes" now in use, spanning a host of industries and sectors. A node may be a master or slave. Each has a unique node number or address and the master can send information (commands) to a number of slaves. The master also receives information from the slaves and usually contains an application-specific program.

AC drives are always slaves. The method of communication from master to slaves varies according to the protocol selected, i.e., polling, cyclic, point-to-point, strobe, query and answer. Each communication link will also have a transmission speed (Baud rate), in either Hz or bits/second and the master device usually determines this.

Trends in Fieldbus and Drives
While the technology for simplifying the way field equipment is linked to the host controller has been around for more than a decade, the focus on fieldbus links to AC drives have intensified and, now, are a mainstream consideration for facility and plant engineers, according to Weingarth.

In the absence of a single international protocol, drive manufacturers (and other device vendors) simply are providing the fieldbus technology customers need to complement the automation system they have or plan to install. The onus of that responsibility definitely lies with manufacturers, Weingarth noted. This has resulted in many different industrial protocols; the following, which ABB supplies in complement to the full array of ABB drives, are among the most recognized today:

Wide Array of Control Benefits; Easy Cabling
Features built into these fieldbuses help end users achieve a critical objective manufacturing flexibility. Key features include a wide variety of function settings/drive control, drive monitoring (via parameters and/or actual signals), drive diagnostics, parameter handling (for set ups or downloads), serial communications for easy expansion with later machine additions, and simple cabling. Engineers use a simple two-wire cable to connect an automation system to an ABB drive, Weingarth noted. Such single-point connectivity saves the costs required with traditional VFD hard wiring to multiple control points, he said. Its a significant savings and you eliminate all the work of the hard wiring.

ABBs latest line of motor drives, the new ACS 800 DriveIT Low Voltage AC Drive family, utilizes a snap-on module, which mounts easily inside the ACS 800 drive to provide connectivity to automation systems. The wide range of adapters means that users choice of an automation system is independent of the decision to take advantage of all the benefits built into motor drives, note ABB experts. Manufacturers can choose both automation system and drives/motors, notes Weingarth. Fieldbus technology makes those choices compatible.

ABB Inc., Automation Technologies, Drives, Motors and Machines, is the world's largest manufacturer of electric motors and drives. In the USA, an integrated channel of sales representatives, distributors, and system integrators allow ABB, New Berlin, Wisconsin, to supply a complete line of energy-efficient electric drives, motors and engineered drive systems to a wide range of industrial and commercial customers. Products manufactured include AC variable speed drives for electric motors from 1/2 through 135,000 HP, large AC machines and drives, medium-voltage drives, power electronics and rectifier systems, AC & DC motors, and application-specific drive system solutions to meet diverse customer needs (http://www.abb-drives.com).

ABB (www.abb.com) is a leader in power and automation technologies that enable utility and industry customers to improve performance while lowering environmental impacts. The ABB Group of companies operates in more than 100 countries and employs about 146,000 people worldwide. The company's U.S. operations employ more than 14,000 people in manufacturing and other facilities in 40 states.

Automation.com Real-time Information for the Automation Professional May. 25, 2012

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