PLCs Adapt, but Will They Withstand Assault of PCs?

Rumors of the death of programmable logic controllers (PLCs) may be—as Mark Twain said—greatly exaggerated. Originally called programmable controllers ("PC"), the PLC has been the foundation of factory control for almost 30 years.But technological battle lines have been drawn. Only a few years ago, few engineers would have considered using a personal computer (PC) for machine ...

By Gary A. Mintchell, CONTROL ENGINEERING May 1, 1998


Machine control


Programmable logic controllers (PLCs)

Sidebars: GE Fanuc announces VersaMax

Rumors of the death of programmable logic controllers (PLCs) may be—as Mark Twain said—greatly exaggerated. Originally called programmable controllers (“PC”), the PLC has been the foundation of factory control for almost 30 years.

But technological battle lines have been drawn. Only a few years ago, few engineers would have considered using a personal computer (PC) for machine control. While great for graphical display and data collection, PCs, with the potential for the dreaded “blue screen of death,” struck fear in the hearts of those responsible for keeping production lines moving.

Technology advances and PCs improve. Users are now intrigued by the idea of open systems. A PLC system is reputed to be a proprietary system; that is, the entire system must be purchased from one supplier. Once a platform is specified, changing to a different platform is difficult.

Open systems

Open systems imply the user can buy components from many vendors. The user can search for the best price-per-feature for the unique application being designed, no longer tied to just one source. PCs are supposed to be these open systems.

A word of caution for buyers regarding open systems: “open” seems to have a lot of definitions. When buying an open system, it is best to understand just what is meant by open.

PLC manufacturers are not ready to concede defeat to the PC supporters quite yet. There is a large installed base of product in use. Engineers still expect support as well as new solutions using this well-known platform. Then again, who’s to say that PLCs can’t become “open?”

PLC manufacturers indicate that there is still a lot of life in the PLC platform. The PLCs of tomorrow may have little technological similarity to their ancestors, though.

PLCs adapt to survive

Look for increasing functionality in inexpensive microcontrollers. With networking now seen as indispensable to modern control architecture, PLC manufacturers are adapting by adding network adaptors. It is also possible to find the wolf in sheep’s clothing—PCs looking like PLCs.

Engineers are seeking ways to reduce the number of different types of components necessary for a control system. They can now find increasing integration of technologies, motion control for instance, into the PLC.

Eddie Prince, Siemens Energy & Automation’s (Alpharetta, Ga.) PLC product marketing manager, sees the combination of miniaturization of controllers with field-device communications opening up a host of application possibilities for distributed control.

Mr. Prince thinks it is likely that Internet technologies using Microsoft Windows CE or Sun’s Java platforms will migrate to PLC control. Siemens’ concept of “Totally Integrated Automation” is a technology that “seamlessly integrates PLCs, operator panels, drives, PC-based control software, control devices and instrumentation to solve a wide range of automation problems.”

The new Siemens Simatic M7 is a hybrid approach. It is a personal computer in the form factor and design of a PLC. It can be used as a PLC programmed in C. Siemens integrated Borland C into the Step7 programming software so that M7 can control I/O modules on the backplane. This controller can also perform all the usual PC functions of networking and data management.

Shared logic

Dave Johnson, vice president of the controller business for Rockwell Automation (Mayfield Heights, O.), looks at the user and notes, “People just want to do control reliably and consistently. How it is done is just a means to an end. Problems may be solved through a variety of means. We focus on doing control in a consistent way.”

Mr. Johnson continues, “We think a significant trend during the next few years will be PLC functionality migrating into other devices—to the point where it’ll be unrecognizable when compared to today’s systems. The logic engine component of control has, until now, been centralized in a traditional PLC or PC form factor. That logic will begin to be shared, moved, and integrated into more devices within the control system. In the future, we’ll see embedded logic in an I/O module or a drive.”

Rockwell Automation’s position is to provide a consistent method of control across the entire range of Allen-Bradley “Logix” vehicles. Instead of tying themselves to a single platform, users can choose the proper control for the specific application and unique problem to be solved.

Robert Oglesby, president of Host Engineering (Johnson City, Tenn.) a member of the PLCDirect (Cumming, Ga.) federation of companies, sees a blending of PLC and PC technologies coming. “PLCs have the rugged form factor required in industrial applications while PCs have strength in programming languages,” he states. “The PLC will likely transform into the ideal platform for PC-based control.”

Regarding open control Mr. Oglesby notes, “The short-term trend in PLCs is the marriage of new PC-based application development technologies with the tried and true form factor of the traditional PLC. While most vendors equate this to ‘open’ systems, it’s really just about bringing to the PLC world what the PC world had almost from the beginning—standards.”

As to the benefit to users, Mr. Oglesby says, “Never before have we had so much powerful, easy-to-use software…or platforms with greater power and lower prices than now. In a market traditionally plagued by proprietary boundaries, standardization will produce a wealth of low-price, high-performance hardware and software.”

Open control from PLCs

John Connor, Quantum product marketing manager for Schneider Automation Inc. (North Andover, Mass.), sees openness as the significant trend in PLCs. Openness is manifested in the growing standards of programming languages and networking. IEC 1131-3 is evolving as a world-wide standard for programming PLCs with the goal of making programs portable from platform to platform (look for a feature in December 1998’s Control Engineering ). Ethernet is the acknowledged standard networking protocol for personal computer networks today.

Mr. Connor sees PLCs historically as a method of taking a popular commercial technology and making it functional for manufacturing plant floor use. Since the currently hot personal computer technologies include networking—especially Ethernet TCP/IP protocol and Internet/intranet—users should expect to see these new technologies popping up on a PLC platform. For instance, Schneider Automation has an Ethernet card with a built-in web server for its Modicon Quantum series.

“Some PCs will be used in manufacturing control applications,” continues Mr. Connor. “The PLC will adapt as it always has and provide control, developed specifically for the factory floor, designed and supported by manufacturers focused on the needs of the engineer and technician.”

Trayton Jay, director of PLC marketing at Mitsubishi Electric Automation Inc. (Vernon Hills, Ill.), sees market demand for broader functionality at a lower price. Such features as motion control, process loop control, floating point math, and trigonometry are now standard in small controllers. Mr. Jay also sees the market demand for better communications ability and for programming standards. Ethernet as a standard communication protocol for computers will be increasingly used for control communication as well.

“PLCs have comparatively simple and generally very reliable hardware,” states Mr. Jay. “PCs will capture more of the large system market, especially when heavy data processing and operator interface functions are required.”

“Users want the openness offered by PCs to be combined with the ruggedness of PLCs,” observes Jeff Meyers, PLC product marketing manager at Omron Electronics Inc. (Schaumburg, Ill.). “Manufacturers want to integrate the PLC to the same network as their computer and MRP [manufacturing resource planning] systems by using Ethernet, particularly because the technology is so affordable now. As a result, control system suppliers are developing hybrid PLC/PC systems.”

Mr. Meyers points out one potential downside to this trend. PLCs may begin to have shorter lifecycles like those that exist in the PC world.

More versatility wanted

Cutler-Hammer/Eaton product line manager (Columbus, O.) Dennis H. Shreve reports three trends driving PLC developments. “The first is packaging. Everything needs to be done in a flexible, building-block style. Second is processing power. The CPU must have a faster logic processor, more memory, more I/O capability, a real-time clock, and special functions. Third is versatility in I/O types.”

Expect to see more focus on open architecture and embedded controllers. Mr. Shreve also predicts smarter I/O devices which will distribute intelligence to lower levels of the system, increasing system speed and accuracy.

Mr. Shreve sides with those who think that PLC technology will be around for a long time by adopting new technologies for new applications. Users will benefit from the changes in PLCs in many ways. System performance will improve, as will reliability. System costs will be reduced through lower component prices and reduced wiring runs. Built-in intelligence will improve diagnostics and troubleshooting. High-speed processing and distributed intelligence will improve process monitoring and control.

Stephen Luft, Entertron Industries Inc. (Gasport, N.Y.) vice president, sees a bright future for the microPLC market. Microcontrollers are a trend for the future, but they must continue to evolve. Features such as real-time clock, floating point math, and fieldbus connectivity are being added to the product line to stay abreast of demand. Packing more I/O points, especially more flexible discrete/analog combinations, will be essential for competitiveness.

Aromat Corp. (New Providence, N.J.) product engineer Junji Ichiryama points to the increasingly smaller controller sizes with increased processor speeds and broad functionality as evidence of the trends Aromat sees in the PLC market.

SoftPLC Corp. (Houston, Tex.) implements a PLC without necessarily selling hardware. This software PLC looks like a traditional PLC to the programmer but is implemented on an industrial PC. Dan Hollenbeck, president, predicts that Java as an embedded controller will be an important future trend.

The SoftPLC example reveals the problems in attempting to categorize the market now. Certainly PLC and PC hardware along with software advances are continuing to blur traditional distinctions of types of control.

As Schneider Automation’s John Connor points out above, the future tends toward taking commercially available technologies packaged for the industrial user. This is happening now. The PLC is alive and well, and users of control products have more choices than ever.

GE Fanuc announces VersaMax

The VersaMax DIN-rail-mounted controller and I/O system has been launched by GE Fanuc Automation Inc. (Charlottesville, Va.) This new platform was introduced at the 1998 Hannover Fair.

Market research from Automation Research Corp. (Dedham, Mass.) and others revealed a gap in offerings for a fast-growing segment of the market—28- to 128-I/O points. This product, which controls up to 256 points, was designed to bring the power of larger systems to this market.

According to Vincent Tullo, vice president of the PLC business, GE Fanuc utilized its Design for Six Sigma process to assure that the product would meet that standard in reliability, quality, and critical to customer standards. The design goals were determined after interviewing over 80 control users around the world. Goals included increased speed and power in the controller, as well as flexibility and scalability for the system.

The PLC is small and can be networked as a master or a slave. Eight I/O modules can be mounted to a CPU. The design is rackless. Modules just snap in place. The system features hot insertion which allows users to add and remove I/O modules from their bases while a process is running without affecting field wiring. The CPU automatically recognizes system changes or additions and autoconfigures for the change.

VersaMax programs with the familiar Cimplicity Control which supports any of the IEC 1131-3 languages. Floating point math, real-time clock, PID, subroutines, and capability for motion control are all supported.

Ports include RS-232/485, Series 90, and Modbus RTU slave. At release, VersaMax will also support DeviceNet (as a master), Genius (slave and peer-to-peer), and Profibus DP with support for Interbus, SDS, and other industrial network protocols to come.

VersaMax I/O modules can be connected to the VersaMax PLC or used as remote I/O for other GE Fanuc PLCs. With network interfaces from GE Fanuc for most other fieldbus systems, the VersaMax I/O system can be used as remote I/O for control systems from competitive PLC or PC suppliers. Extensive diagnostics are provided. To simplify wiring, a wide variety of wiring termination options are offered.

The I/O family features discrete points with both ac and dc voltages in 8, 16, and 32 point densities. Inputs accept high-speed counters which can be used with encoders. The analog modules are voltage/current selectable, isolated with 16-bit resolution. RTD and thermocouple inputs are also available. The bases snap together and are DIN-rail mountable. Bus addresses are set with a rotary switch—no programming is required. A module can contain both analog and discrete points with a wide variety of mixed I/O modules available at product launch.

VersaMax will be globally certified at launch including CE, UL, CUL (Canadian UL), and Class 1 Division 2. All information on the products is laser engraved with no adhesive labels used meeting European environmental laws. Product availability is set for third quarter 1998.