Programmable Logic Controllers

In a society where survival of the fittest is prevalent, companies are looking towards the future for the most reliable uses of industrial computation. Responding to trends with industrial computers, manufacturers are adding more functionality to smaller and faster programmable logic controllers (PLC)s, that, in some cases, blend and work with PC-based software.

02/01/2001


In a society where survival of the fittest is prevalent, companies are looking towards the future for the most reliable uses of industrial computation. Responding to trends with industrial computers, manufacturers are adding more functionality to smaller and faster programmable logic controllers (PLC)s, that, in some cases, blend and work with PC-based software.

'In the past, when users requested a controller to fit their application, that control choice typically required an implementation unique from previous choices the OEM or user had made. But that's all changed. Advancements in controller technology now make discrete, drives, motion, and process control possible with a single, integrated control platform,' says John Nesi, Logix/NetLinx strategic marketing manager for Rockwell Automation (Milwaukee, Wis.)

Jay Ward, PLC product development, Schneider Electric (Palatine, Ill.) says, 'As a natural progression driven by technological advances and adoption of open standards, the market is moving towards optimization of the process to increase productivity.'

From a natural progression of technological advances to the need to integrate various tasks, manufacturers iterated the same requests from customers: the desire to have open connectivity, productivity, and scalability.

Mr. Nesi says, 'What's important to most users today is ability to seamlessly integrate different applications across their plant that traditionally needed different types of controllers.'

He adds, 'New controllers save engineering maintenance costs, and improve communication across the plant floor.' This brings about plant-wide integration that maximizes productivity and throughput, he says. 'OEMs that can offer those benefits will continue to thrive.'

Tom Schermerhorn, vp of the systems group at Control Technology Corp. (Hopkinton, Mass.) agrees that integration is the next important step in the PLC industry.

'The ability to integrate multiple aspects of control-I/O points, motion, and communications, into one system and one programming environment is critical to customers,' says Mr. Schermerhorn.

Control Engineering polled 1,500 readers, in part, to learn more about the changes occurring in the programmable logic controller industry. Two hundred seventy-six completed the survey resulting in an 18% overall response rate.

Objectives of the survey were to examine the type of programmable logic controllers used; determine the major applications for PLCs and how they interface with other control systems; and qualify respondents' involvement in recommending, specifying, and/or purchasing PLCs.

Seventy-four percent of respondents recommend, specify, and/or purchase PLCs for in-plant requirements; 16% do so for OEM (resale) requirements.

Sized by input/output (I/O) capabilities, Micro (less than 128 I/O) was the most used PLC type at respondent companies at 80%. Medium-type (128 to 512 I/O) was used by 70% of locations. Large-type (greater than 512 I/O) was used at 41% of locations.

Machine control, 87%, and process control, 58%, were the leading applications for programmable logic controllers. Motion control was third with a 40% response. Diagnostics was the least used primary application for PLCs, mentioned by 18% of the respondents. (See graph.)


How time flies

Early PLCs' only function was to manipulate relays wired to its discrete inputs. (See CE , Oct. 1995, 'The Evolution of PLC-Based Loop Control,' p. 57.) Thirty years later, they remain a steadfast and growing component to various industries.

Jim Spencer, general manager for Lipten, a power generation company based in Wixom, Mich., says, 'PLCs fit the bill of replacing single-loop controllers. They provide flexibility to do all data acquisition, assist the DCS without high cost, are popular within other industries which, gives allowance to a greater familiarity among customers.'

Along with flexibility, speed has become another important development in PLC and I/O technology.

Paul Ruland, PLC and I/O product manager, Automationdirect.com (Cumming, Ga.) says, 'The industry first delivered Ethernet communication modules for large, expensive PLCs. But more recently, less expensive 10Base-T and 10Base-F PLC Ethernet modules have become available, along with Ethernet slave modules for field I/O nodes in PC controls and hybrid systems.'

When asked which I/O modules respondents used, 91% answered analog, 81% discrete, and communications 62%. High-speed counter and PID were used 44% and 43% of the time, respectively.

Future plans for programmable logic controllers include PLCs with more remote I/O modules, 40%; PLCs with more plug-in modules, 37%; PLC I/O networked to PCs, 29%, and more micro PLCs, 26%.


PC-based, or not

The future of PLCs seems bright, and, some say, the jury is still out on whether or not PC-based solutions will dominate future industrial control.

'PC-based controls will play an important role until PLCs and PLC-type systems become more open, intelligent, affordable, and move away from proprietary networks. Users demand the kind of flexibility that PC-based systems launched, the ability to change software layers without changing hardware, and to use commercially available technology whenever appropriate or possible,' says Benson Hougland, director of technical marketing for Opto 22 (Temecula, Calif.).

David Harris, product-line manager for Eaton Cutler-Hammer (Cleveland, O.) agrees about the influences of PC-control.

'We have seen an increase in PC-control systems over the past year. I believe technology is getting easier to apply and therefore is getting increased acceptance,' says Mr. Harris.

However, like the early days of PLCs, not everyone is jumping on the PC-control bandwagon.

'PC-based control is still in the hype stage. It can be very expensive and oftentimes not reliable on a factory floor. PLCs are much easier to repair and have a longer life cycle than PCs. PLCs don't lend themselves to problems,' says Don Sondermann, PLC product marketing manager, Omron Electronics (Schaumburg, Ill.).

Opinions obviously differ widely, even as many PLC manufacturers offer PC-based solutions, some industrially hardened. So what can users expect to see in the future?

'Customers want a simplified way to deal with large-scale issues that increasingly effect their process automation project decisions. Those issues include globalization, technological change, and ever-increasing customer requirements. That requires process control engineering and management software solutions with full distributed control system functionality,' says Schneider Electric's Mr. Ward.

Jason Gloeckner, product manager for Eaton Cutler-Hammer says, 'PLCs have been around for quite awhile now in the industrial market. I believe new uses for PLCs, as they get lower in cost and expand in technology, would be the residential market. I see numerous applications where large houses and schools are now being run by PLCs. Everything from lighting systems, heating, cooling, and alarm systems.'

Mr. Gloeckner adds, 'I believe Ethernet will need to be the standard on PLCs in the future. It has been debated for quite some time that Ethernet will never be accepted into the industrial market due to non-deterministic protocol fashion. Although at 100 Mbit per second, does it really matter?'

And beyond speed, deterministic Ethernet solutions have been made available.

Programmable Logic Controller Products

For more information on programmable logic controllers, circle the following numbers, or visit www.controleng.com/freeinfo . For a broader listing of PLC manufacturers, go to the Control Engineering Buyer's Guide at www.controleng.com/buyersguide .

Family now includes smaller platform

Milwaukee, Wis. -Allen-Bradley CompactLogix 5320, a small, modular control processor, is designed for OEMs seeking standalone, machine-level solutions, such as packaging and conveyor applications with limited I/O count and communications capabilities. CompactLogix is part of a complete system-level architecture that uses the same Logix control engine shared by ControlLogix, FlexLogix, and SoftLogix. It also employs the same RSLogix 5000 programming package as other Logix platforms, enabling users to move from one application to another with minimal additional program development and training. An RS-232 port provides direct connection for programming, operator interface devices and ASCII devices, as well as dial-in remote programming. www.rockwellautomation.com

Rockwell Automation

Versatile Ethernet remote modules

Cumming, Ga. -Ethernet Remote Master (H2-ERM) module, connects local CPU bases to remote slave I/O points over a high-speed link. The module, for use with Automationdirect.com D2-240 and D2-250 PLCs, and its line of WinPLC Windows CE CPUs, can support up to 16 additional DL205 bases, 16 terminator I/O systems, four expanded DL405 systems, or any combination of the three. One module version connects to a control network using Category 5 UTP cables and cable runs up to 100 m. A fiber-optic version uses industry-standard 62.5/125 ST-style fiber optic cables and can be run up to 2,000 m. www.automationdirect.com

Automationdirect.com

Configure without a computer

Charlottesville, Va. -VersaMax EZ Program Store device enables users to perform program and configuration field upgrades to VersaMax modular CPUs without a computer. EZ Program Store accessory, a recent addition to the VersaMax family of PLCs, is compatible with CPUE05, CPU005, and supports VersaPro 2.0 programming software. EZ Program Store is designed to make it easy for OEMs to upgrade customers without travel. Hardware features include a 15-pin, D-shell connector to the modular controller programmer port, an activation button to initiate storing sequences, an indicator LED to show storing status, and a light-colored, textured surface for content marking. www.gefanuc.com

GE Fanuc Automation

PLC with look, feel of embedded controller

Schaumburg, Ill. -Users can save time and cost of building their own boards from scratch with Omron's CPM2B Series microcontroller. With features such as back-up battery, advanced communications, expandability to 128 I/O points, RS-232C port, removable terminals, and PID, the CPM2B is said to offer flexibility, expansion options, and proven operating and programming systems. www.omron.com

Omron Electronics Inc

Fault-tolerant system reacts in milliseconds

Alpharetta, Ga. -Simatic S7-400F, said to be a failsafe version of the high-performance S7-400 programmable logic controller, is designed for applications where protection of personnel, equipment, or environment is critical. In the event of a critical situation, the controller goes into a user-defined safe state for an orderly shutdown, while providing extended diagnostic data to facility operators with safety-related functions and reaction times in the range of 200-500 msec. S7-400 hardware is based on the CPUs of the fault-tolerant Simatic 400H redundant system that can be used with one or two channels, according to required safety levels. Simatic S7-400F safety I/O racks are incorporated into the system via Profibus with a safety rated protocol. www.sea.siemens.com

Siemens E&A

Portable PLC for test labs

Stamford, Conn. -OM-LMPLC functions as a flexible I/O controller for test labs. It was specifically designed for on/off cycling tests such as pneumatic, electronic power, and other durability testing. The front panel has two buttons, key-switch, connector, and display. The rear panel has connections for bidirectional LED opto-isolator inputs, outputs available for dc and ac power, and the device power. All user interactions occur through the front panel. Included with OM-LMPLC is Procedure Writer software, which allows the end-user to easily build procedures to control outputs with complex logic. www.omega.com

Omega Engineering





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