PLCs become small, fast, smart (Expanded Version)

By Control Engineering Staff November 10, 2004

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Expanded Version Programmable logic controllers (PLCs) are the logical choice for many control applications and, like many technologies in automation, continue to shrink in size, increase in function, communicate more, and integrate well with other forms of industrial computers.

For these and other reasons, Control Engineering subscribers plan on buying more PLCs in the coming year, according to those responding to a recent Reed Research Group survey. Among the 202 respondents who specify, recommend, or buy PLCs, 59% do so for in-plant requirements, 19% for OEM needs, and 22% for both.

Forty-five percent of respondents said they will increase PLC spending, 49% remain the same, and 6% expect a decrease; in 2002, just 29% expected to buy more, 64% remain the same; and 7% decrease.

The survey also showed that wireless connections to PLCs are expected to increase drastically in the coming year; Ethernet use also will increase.

Popularity of PLCs sizes (by number of I/O) stayed about the same in 2004 and 2002; but use of PC-based control and soft-logic controls increased a bit. Micro PLCs (16 to 128 I/O) accounted for 27%, medium-sized PLCs (129 to 512 I/O) 27%, large PLCs (>512 I/O) 18%, PC-based controllers 10%, nano PLCs (under 15 I/O) 7%, soft logic 7%, and embedded 4%.

Mike Miclot, Logix marketing manager for Rockwell Automation, says some increase from PC-based control and soft logic is “not surprising, and can most likely be accounted for by organizations moving from traditional‘home-grown’ control systems, to implementing and adopting off-the-shelf solutions.”

More PLCs are being used in process and batch applications, a trend Miclot also doesn’t find surprising, “as customers begin to realize that a DCS is overkill for batch operations.”

Respondents in 2004 are using PLCs for process control and machine control equally at 72%, motion control 45%, batch control 36%, diagnostics 19%, and other uses 6%. These figures are virtually the same as in 2002 except for machine control, which then accounted for 79% and batch control at 31%.

More PLCs are being connected to PCs and fewer are used in strictly stand-alone applications, perhaps two sides of the same trend of increased information sharing. Answering the question: “How do most PLCs interface with other systems?” respondents said—network with personal computers 30%, stand alone 29%, network with other PLCs 24%, networked with distributed control system 18%.

In 2002, it was stand alone 34%, networked with PCs 26%, networked with other PLCs 24%, networked with distributed control system 16%.

Nick Infelise, PLC product marketing manager, Omron Electronics, says advanced communications makes “it is easier for manufacturers to share data and have single point of access to plant floor. Looking at present and future use of communications protocols used with PLCs, users anticipate less serial, more Ethernet, and a lot more wireless. Leading ways of communicating with PLCs are: serial RS-232/RS-485 89%, Ethernet 86%, and 4-20 mA/0-10 V dc 81%.

PLC communications are also improving predictive maintenance, with “status and diagnostic capability built-in to remote devices on I/O networks, safety networks, and direct access to remote networks from a single point to speed debug,” Infelise adds.

In 2004, among those saying they use Ethernet, 79% use it as a supervisory network. Nearly two-thirds (65%) use it to network PLCs; 44% use it for controlling I/O devices 44%.

Among those who use Ethernet, 83% use TCP/IP; EtherNet/IP stands at 54% and Profinet at 7%.

Among favored programming languages, ladder diagram remains dominant. Even so, Connie Chick, business manager for controllers, GE Fanuc Automation, notes that “expansion of programming tools, including function block diagram and sequential function chart, increase control engineers’ options of the application functionality, all while minimizing the project timing impact.”

In 2004, ladder logic accounts for 94%, function block 44%, SFC 22%, structured text 21%, C programming 18%, flow chart 14%, instruction list 11%, and other 1%.

In 2002, ladder logic was 96%, function block 38%, SFC 17%, flow chart 14%, C programming 18%, instruction list 12%, structured text 15%, and other 2%

Built-in communication support is far and away the most important factor to survey participants in 2004 when buying a programmable logic controller CPU at 78%; total memory 53%, scan time 52%, PID 49%, motion support 24%, removable memory cartridge 16%, and wireless capability 6%.

Built-in communications and motion support each were six percentage points higher than result of the 2002 poll.Most important features for future PLC purchases among 2004 respondents are more remote I/O subsystems; universal programming software for multiple hardware targets/platforms; integrated I/O modules; I/O networked to PCs; and Web-enabled PLCs.

Feature sets such as expanded controller memory, built-in communications support, PC-like application mobility and motion support all aid control engineers’ options for applications, as well as increasing project return on investment, Chick explains. “The controller now has built-in functionality;” additional equipment, such as second CPUs, communications cards, and conversion programs now are unnecessary, she adds.

On features, Miclot says he sees increased “use of removable memory cartridges, for example, Compact Flash cards in Logix controllers from Rockwell Automation. Removable memory cartridges expand functionality and provide flexibility in applications. This enables OEMs to create entire projects, burn them onto the compact flash card, and mail it to the installation. For end users, it means lowering mean time to replacement, because during a hardware failure, the maintenance engineer simply takes out the old compact flash card and inserts a new one.”

Infelise, says users can expect more advanced motion control and process control from PLCs “without burdening the CPU scan.” In addition, the PLC experience continues to get easier with function block and structured text programming capability, built-in libraries, and more flexible and intuitive software for PLCs and SCADA, he says.

PAC: PC w/PLC ruggedness

Programmable automation controllers (PACs) are said to combine the packaging and ruggedness of a PLC with software flexibility and functionality of a PC.

“Applications for industrial controllers vary greatly in their requirements for domain functionality, communication protocols, interface needs, programming language and feature sets within a plant or OEM machines,” says GE Fanuc’s Chick. “That is why control engineers are looking for multi-domain functionality in automation controllers with universal programming, increasing functionality while minimizing project-timing impact. A multi-domain controller with a common development platform can reduce overall training requirements and time to deployment for all applications in a facility.”

To gauge survey respondent’s PAC understanding, the Control Engineering survey asked, “What do you consider a programmable automation controller to be?”

Exactly 30% chose “Like a PLC but more‘open’”; 29% said a “PC-based processor in a rugged PLC-like package”; 18%, “A superset of PLCs”; 17%, “A subset of PLCs”; and 33%, “Not sure.” Addition shows that more than one answer was allowed; “correct answers” were the first two choices, or the last one.

Programmable automation controllers—if they hope to tout PAC advantages to those who purchase PLCs—need to better differentiate PAC features and functions from traditional PLCs. But most traditional PLCs now part with tradition. Perhaps function now trumps form, and there’s less need to use names for logic devices: PLC, PC-based controller, PAC, DCS, embedded controller, and loop controller. “Just give me a dozen of those, please.”

PLC products

Visit for more manufacturers; for system integrators, go to Also visit the Web sites of the products listed.

EXCLUSIVE: PLC gets 100 Mb Ethernet I/O modules

AutomationDirect offers a 100 Mb Ethernet I/O base controller module and 100Mb Ethernet communication module for DirectLogic PLCs. Modules are priced at $299 each.

The H2-EBC100 Ethernet Base Controller module is said to provide a low-cost, high-performance Ethernet link between DL205 I/O and any PC-based control, SCADA, or monitoring system, or any WinPLC/DL205/ DL405 CPUs using AutomationDirect’s Ethernet Remote Master module for remote I/O points. It also can be used to connect DL205 I/O points to a Modbus TCP/IP client (master) and is compatible with TCP/IP, IPX, and Modbus TCP/IP protocols for PC communications. EBC modules are said to offer virtually unlimited I/O points, deterministic I/O updates on dedicated networks, and fast I/O updates (&1 ms per base). On-board serial port can connect to operator panels, ASCII in/out, and other devices.

H2-ECOM100 supports Modbus TCP/IP client/server, IP, and IPX protocols. The module can actively issue commands to other nodes or devices on the Modbus TCP/IP network or respond to other connected Modbus TCP/IP clients.Each may be configured with free NetEdit software utility or via HTML from a browser. Additionally, DHCP server support is included, providing a way to allocate IP addresses dynamically to the modules on a local area network. AutomationDirect

Controllers integrate ControlNet

Allen-Bradley CompactLogix 1769-L35CR and 1769-L32C controllers offer integrated ControlNet network connectivity, which eliminates need for modular communications, simplifies programming, and cuts installation and configuration costs. The CompactLogix 1769-L32C will be available in early 2005. Using one software package, users can configure the ControlNet network and bridge from ControlNet over to DeviceNet to configure devices on DeviceNet from one access point. When users apply power to the controller, the ControlNet device is configured automatically, eliminating previously required steps to install, configure, and add a scanner module to the programming tree.

CompactLogix 1769-L35CR offers redundant media to provide greater reliability in complex applications. It supports up to 30 local I/O modules and offers 1.5 MB programming memory for powerful capacity in a small package. CompactLogix 1769-L32C is designed for smaller scale, single media applications, supporting up to 16 local I/O modules and providing 750 KB of programming memory. Rockwell Automation

Motion control PLC 317T Integrated Technology PLC combines technology and motion control into one Simatic PLC. Using Siemens Step 7 software technology, the devices needs only one program for PLC and motion control, simplifying configuration and programming while reducing training and hardware costs. The 317T can control up to 16 axes. Motion control functions available include positioning in absolute, relative, additive, and superimposed operating modes. Other functions include geared synchronous motion, electronic cam disc and cam functionality, moving to a positive stop, and measuring probe functionality (used for print mark correction). Siemens Energy & Automation

Multiple network controller

PACSystems RX3i controller runs on a high-speed, PCI-based backplane and Intel Pentium 300 mHz CPU. High-capacity power supplies can be deployed in single or multiple configurations to provide adequate power or redundancy in one rack. It also features faster I/O capabilities with expanded diagnostics, interrupts, and hot insertion. The system supports a wide range of I/O modules and includes discrete, universal analog, high-density analog, high-speed counter, and motion. Extensive communications capabilities include integrated Ethernet and Profibus modules as well as support for DeviceNet and Genius networks. RX3i allows combination of new technology with existing hardware systems, providing a seamless migration path for GE Fanuc customers. Proficy Machine Edition software provides a universal engineering development environment for programming, configuration, and diagnostics for the entire PACSystems family. Proficy has tag-based programming, a library of reusable code, and a test edit mode for improved online troubleshooting. GE Fanuc Automation

PLC programming software Version 2.0 of Telemecanique Unity Pro is said to provide versatile IEC 61131-2 PLC programming, debugging, and operating software for Modicon PLCs down to the micro level, and adds a variety of ergonomic improvements to reduce design development times. Now available in multi-seat licenses that enable as few as three or as many as 100 users to collaborate in control system design, operation and maintenance, Unity Pro 2.0 software facilitates integration across disciplines, enabling individuals and teams to share ideas and information visually. Other Unity Pro 2.0 features include reduced file sizes for faster processing, new hot-standby capabilities, a built-in interactive operator screen to streamline maintenance, a full-function simulator to enable bench-testing of applications, and user-defined function blocks to simplify programming. User-definable Ethernet protocols allow direct connection to RFID tag stations, barcode readers, and competitive PLCs, making it unnecessary to add gateways. Schneider Electric

Duplex PLC provides redundancy, speed

CS1D duplex programmable controller builds on the high speed and reliability of the CS1 controller by adding redundancy. Should a problem arise in the primary CPU, the CS1D automatically switches control to the second unit within one program scan, enabling continuous operation. The down CPU can be changed out while operation continues. Redundant power supply and communication modules can be removed and replaced without interrupting control operation. Continuous operation is enhanced by “hot swappable” I/O and specialty modules. It is configurable as a redundant CPU only, or as a complete duplex system with redundant power supply and communication modules. Communications are automatically switched to the standby unit if a failure occurs in the primary module. CS1D is compatible with CS1 Series I/O units. High reliability applications include wastewater processing applications and semiconductor fabs. It also speeds restoration following a failure. A basic CS1D system is available from stock starting at $11,500. Omron Electronics

Q Series offers redundancy Q Series Automation Platform with full redundant hot back-up capabilities is expected to begin shipping by the end of 2004. Key features include dual redundant processors, dual redundant networking, and hot swap capability. Automatic, user-defined synchronization of process data between redundant processors ensures “bumpless” transfer of control. Dual redundant network capability allows deterministic performance up to 25Mbit/s between controllers and I/O. Power supplies are also redundant. Redundant Ethernet communications maintain communications to SCADA systems after switchover. No special hardware is required beyond redundant processors; standard Q Series parts can be used on regular and redundant Q systems. Redundant CPUs are physically separate, allowing offline CPUs to be serviced without interrupting the process. Mitsubishi Electric Automation

Scan times increased KV-300 series PLC is one-third the volume and requires only one-half the footprint of conventional units. KV Quick Scan method controls all I/Os with a fast 0.5-ms scan time, overcoming scan-time delays of conventional wire-saving systems. Modular design allows DIN-rail mounting and employs a quick-disconnect lock mechanism. No additional rack or base is required when extending the system configuration. One computer running Keyence Ladder Builder Software can communicate with multiple CPUs to edit programs, monitor operations, or monitor a CPU while communicating with another computer. Free programming software includes an editor for easy editing with Microsoft Windows functions and a monitor for real-time monitoring without stopping the machine. Keyence

Controllers embed Internet CNi3222 controller offers embedded Internet (EI Option CNi16D Series) for $195. The family has RS-232/485 communications, programmable color displays, five-year warranty, free software, ActiveX controls, and selectable full auto-tune PID control. It has two outputs: control, alarm or retransmission of process variable. Omega Engineering