RRODUCT RESKARCH

ProgrammableLogic Controllers

Even in a tight economy, PLCs and PACs are hot commodities, a true testamentto their control adaptability, flexibility, and multi-feature capabilities.

With the venerable program-mable logic controller (PLC)marking its 40th anniver-sary this year, I got to think-ing about its timeline. It goes

way back in my engineering career—the careerbefore my involvement with Control Engineeringmagazine. So 1 asked a fellow engineer, whoseinvolvement in the control industry includesmore history than mine, what he thought.

"There's evolution and then there's revolu-tion," said Bill Southard, president and CEO ofDST Controls, a systems integrator from Beni-cia, CA. "Mr. [Dick] Morley sparked a revolutionin machine building techniques with his intro-duction of the PLC (actually then called a 'pro-grammable controller' or 'PC') back around thetime the earth cooled. This created excitementand benefited the machine builder in three verymajor ways," he says;

• The first and foremost benefit was thereduction of time it took to design, prototype,and then build a machine. This benefit wasderived from the fact that the logic could actu-ally be worked out while the machine and con-trol panel were being built, not after all the relaylogic diagrams were completed and checked.

• Secondly, machine builders could easilyreprogram the PLC to add new features to bothnew and existing machines, thus extending thelife of the products.

• Lastly, the control panels associated withthe machinery could be smaller, making it possi-ble to mount the controls on the machines ratherthan on an entire wall.

"All of the above resulted in significantlylower costs to the machine builders in bothmanpower and hardware," Southard says. Theprogrammable automation controller or PAC(essentially a ruggedized PC in a PLC-like form

Programmable controller types in useLarge (greater than 512 I/O

Medium (129-512 I/O) ' Nano (lest than 151/0)

Dick JohnsonControl Engineering

ONLINE

Micro (15-128 I/O)

For more on the history otPLCs, see p. 66. That PLC40th anniversary article alsocan be found online alwww.controleng.cani/Brchives

under Sept. 2008Source: Conlrol Engineering and Reed Research

Nearly all respondents (92%) will buy PLCs/PACs in the next 12 months. Shown are devices already installed.

WWW.COntroleng.com • CONTROL ENGINEERING SEPTEMBER 2OO8 • 8 3

PRODUCT RESEARCH

The majority of PLCs/PACsare used for embedded

control in machine- orprocess-control

applications.

Major applications of PLCs and PACs100

90

80

I 70

ID

m•5 50

II 40oy

S. 30

20

10

O

79%82%

20082007

25%

Machinecontrol

Source: Control Engineering and Reed Research

factor) is "merely an evolutionary productthat extends the mighty power of the good oldPLC," adds Southard. "Now, it is specificallydesigned for connectivity and distributed I/O,thus continuing to make design easier. But,alas, so do the new terminal block designs.

"Mostly, I see [PACs] as a public relationsmove so that the young engineers of todaydon't have to work on the same hardware theirfathers did. Evolution is a slow process thatoften goes unnoticed without a view of his-tory. Give me a good old revolution any day."[For more history of the PLC, see "How pro-grammable controllers emerged from industryneeds" on page 66 of this issue.)

Revolution or not—evolution or not, the 405respondents who answered the joint ControlEngineering/Keed Research product researchstudy on PLCs and PACs will be increas-ing their purchases of these devices over thenext 12 months. Even with the tight economy,23% of respondents expect their purchases toincrease. Of those polled, 69% expected pur-chases to remain the same as last year, andonly 8% expect them to decrease.

Putting PLCs to workOf the control engineers queried in this onlinesurvey, 54% use their PLCs/PACs for in-plantrequirements, 14% use them for OEM orresale requirements, and 12% use them forboth. Choice of PLC/PAC size was also reflect-ed in this survey. Nano devices (fewer than15 I/O points) accounted for 9.9% of installedPLCs. Micro devices (15-128 I/O points) were

Batchcontrol

installed 38.4% of the time. Medium (129-512I/O points) and large (more than 512 I/O points)were specified 33.5% and 18.2% of the time,respectively. As expected, these figures near-ly mirrored the results of the previous year'ssurvey.

Of these installed devices, the survey foundthat the majority of them were used as embed-ded controllers rather than PCs, data loggers,or SCADA apps connected to PCs. As formajor applications, PLCs and PACs were usedmostly in machine control (79%). Process con-trol (74%), motion control (55%), batch control(33%), and diagnostics (23%) rounded out thesurvey results. See accompanying graph forthese ratings as compared to those of 2007.

When asked how most of their plant's PLCsor PACs networked with other control systems,respondents said the most (29.1%) networkedwith other PLCs, Standalone devices account-ed for 24.4% of the responses. The remaininginterface "partners" were distributed controlsystems (21.4%), personal computers (21%),and other PACs (3%).

Getting them to talkCommunication protocols for PLCs were alsothe subject of this survey. The top ten list ofthose currently used (listed most popular first)is: serial (RS-232 and RS-485), 4-20 mA, Eth-ernet (wired), Allen-Bradley Remote I/O, Devi-ceNet, Modbus, ControlNet, general wireless,BCD (binary coded decimal), and Profibus.

With the current popularity of the Ethernetprotocol in mind, the survey queried control

8 4 • SEPTEMBER 2008 CONTROL ENGINEERING • WWW.COntroleng.com

professionals about their preferences of both type and func-tion of their Ethernet networks. Of those using Ethernet, 70%used it as a supervisory network, 67% used it as controller tocontroller networking, 54% used it to control I/O, and 41%used it for enterprise connectivity.

Ethernet protocols that respondents currently use or plan touse with their PLCs or PACs ran the gamut of those available.They are (in order of popularity): TCP/IP, EtherNet/IP, ModbusTCP/IP, High Speed Ethernet (HSE), Profinet, UDP, EtherCAT,Sercos II, EtherNet Powerlink, FL-net (OPCN-2). A discussionof these protocols can be found in a previous product researcharticle on industrial Ethernet, which appeared in the May 2008issue of Control Engineering.

Languages used to program PLCs and PACs were also a sub-ject of this survey. A tally of the responses made it clear thatcontrol engineers use ladder diagrams almost two-to-one overthe second most popular method, function block. Structuredtext was not a close third, rating less than two-to-one behindfunction blocks. C programming, sequential function charts,flow charts, proprietary software, and instruction lists were allmentioned, with none getting substantial support.

Giving 'em what they want!PLCs and PACs are available with a wide array of features thatallow them to be adapted to applications. A total of 30 differ-ent features were deemed "very important" when selecting aPLC or PAC, as reported by survey respondents. Categories offeatures included communications issues/adaptability, speedymemory capabilities, form factor availability, etc. In order offrequency of selection, the most commonly preferred feature-number one by nearly a two-to-one margin—was built-in com-munications support. Rounding out the list of top ten features(in order of preference) are:

• Scan time• Availability of analog I/O (strain, vibration, etc.)• PID availabihty• Tbtal memory• Availability of universal programming software for mul-

tiple hardware targets/platforms• More remote I/O subsystems• Controller I/O networked to PCs• Motion support• Integrated I/O modules.The overall list included 20 more features that were desired

by control professionals who completed the survey.PACs are considered much more adaptable and powerful

than their predecessor, the PLCs. But have they gained theacceptance of the automation communication yet? Per thissurvey, PAC purchases over the next 12 months exactly mir-rored those reported for the PLC, indicating true acceptanceby the control community. Verbatim responses on the subjectof FLC vs. PAC use were mixed, however. Comments rangedfrom tongue-in-cheek comments to specific advice: "Just call aPLC a PAC, or call a PAC a PLC. There is no real need to usedifferent name." "PLCs are like 'old faithful' and PACs are thenew kids and I'm trying to figure exactly what's better aboutthem and why."

As for specific advice, one control engineer commented, "If

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PRODUCT RESEARCH

Networked with other PACs

-Other

How PLCs/PACs are interfacedwith control systems

Networked with other PLCs

Standalone

Rockwell Automation

Automation Direct

Networked with PCs

Source: ConOoi Enginwring and Reed Researvh

I am using a lot of servos, then I choose a PAC.Otherwise, if the application is just on and off,[I use] a PLC." Another said, "We would usePACs where the functionality of the PLC isbeing extended beyond its engineered, off-the-shelf purpose."

"We don't see PACs being used in that many

Networked with DCSs

SCADA applications. The PAC approach gener-ally offers superior capability when combiningcontinuous and sequential controi. It also shineswhen data anaiysis is important, [or] where adatabase or database interface is important tothe project," said yet another respondent.

Clearly, the control engineering community

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is ready to embrace improving technology. Their message toPLC/PAC vendors is simple—bring it on! In the survey, work-ing from a supplied list, respondents named the following ven-dors as most-purchased-from manufacturers of PLCs and PACs.The list is shown in descending order, along with descriptionsof representative products.

Additional vendors and product descriptions, along with links tovendor Websites, can be found with this article online at www.controleng.com/archives for September 2008. For more manufac-turers, visit www.controleng.com/buyersguide. For complete Prod-uct Research results on programmable logic controllers, click theResource Center tab at www.controleng.com.21

Advanced features,simple configurationTlie Allen-Bradley CompactLogix L23 programmable automa-tion controllers are said to deliver the latest control technologyto small machine-level applications through simplified configu-ration and an advanced set of features. The controllers, whichcome in three packaged forms, offer customers the benefitsinherent in the company's proprietary Logix Control Platform:a common programming environment, common networks,and a common control engine for future control upgrades.Each PAC also features embedded I/O that is preconfiguredfor ease of use. All of the CompactLogix L23 PACs offer 512KBof memory, supporting up to three tasks and four programs.Embedded EtherNet/IP integrated ports are available foradvanced connectivity.www.rockweUautomation.comRockwell Automation

DC output moduleswith fault protectionAutomationDirect's line of DirectLOGIC option modulesincludes new fault-protected output modules designedfor the DL205 PLCs. The F2-16TDxP l6-channel currentoutput modules, available in sinking and sourcing con-figurations, feature 16 input points that are automaticallyassigned as fault status indicators for the correspondingoutputs. Equipped with electronic short circuit protection,the modules detect missing external 24 V dc open load,over-temperature, and overcurrent load. The protected out-put modules also feature user-resettable fault conditions.www.automationdirect.comAutomation Di rect

Distributed controllerwith ProfinetThe new Simatic ET 2Ü0S IM151-8 PN/DP CPU module addsanother processor to the ET 200S I/O family of distributed I/Odevices. Communicating via Profinet, the new CPU is simi-lar in power and performance to the S7-300 line of control-lers. Its built-in Profinet communication interface includesthree ports for linear bus topologies and programming devicefunctions. Communications can also be expanded easily witha Profibus DP master module. As a Profinet I/O controller,the module also supports the real-time properties RT and IRT

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Here's the best part: cATM devices do not require programmingmessage instructions. Configuring the module is as easy as settingup a wireless modem.

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Schneider Electric

(isochronous real time) and can control upto 128 I/O devices. A fail safe version is alsoavailable v̂ 'ith a built-in proprietary ProfiSafesafety network. The CPU can be expandedmodularly in a central rack configuration ordistributed via ProfiSafe on Ethernet for com-bined standard and safety rated applications.www.sea.siemens.comSiemens Energy & Automation, Inc.

Batteryless unit added to lineuses same softwareThe Modicon M340 PLC has been added tothe Modicon Quantum and Premium control-ler lines, with all supported by the proprietaryapplication development software, Unity. TheModicon M340 PLC is said to provide numer-ous cost and performance advantages overcomparably priced PLCs by requiring no bat-tery; offering a compact size (4-in high by3.7-in deep); using high density 64 point I/Ocards that are only 1.254n. wide; and offer-ing pre-terminated cables with flying leads orTelefast connections to reduce wiring time.Additionally, these PLCs use CANopen net-works to reduce field wiring and lower instal-

lation costs, as well as USB cables rather thanproprietary cables. They also feature enhancedprocessing power with 4 MB of memory(upgradeable to 16 MB) and an executionspeed of 70K instructions/ms. They exceedIEC requirements for shock and vibration,www. telemecanique.comSchneider Electric

Open standards,portable control engineThe PACSystems intelligence platform isbuilt to open standards with a portable con-trol engine, a single development tool, anda universal development environment. It issaid to represent a revolutionary change inthe control industry, one that "enables controlconvergence rather than mere integration ofdisparate parts and pieces." Using the PAC-Systems intelligence platform, users can takeadvantage of a powerful engineering environ-ment for multiple operations. The PACSystemsfamily addresses major engineering and busi-ness issues such as high productivity and com-munications openness, and helps users boostthe overall performance of their automation

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New automationplatform on the wayThis fall, Mitsubishi Electric Automation Inc.promises to "advance the state of the art inautomation" with the Q Series automation plat-form. Q Series is a multidisciplinary automa-tion platform that combines all the elementsof common automation systems into onecompact, integrated, and high-performancesystem. The platform combines sequence,motion, process, and PC-based control on asingle, compact, rack-based system. By tak-ing this approach, the system reportedly willintegrate sequence control, complex motionprofiles, and continuous process control whilealso being able to run any third-party PC appli-cation for control, data handling or any otherapplication.www.meau.comMitsubishi Electric Automation inc

Compact PLCwith window inciudedThe Visual KV Series PLC is a high speed, com-pact unit with what is said to be the industry'sfirst built-in access window. The product lineincludes an ac power supply model and anoptional operator interface panel. The new acversion 40 I/O KV is said to be two-thirds thesize of conventional PLCs. Its slim design notonly saves mounting space but allows the entiresystem, including the distribution panel andthe control box, to be downsized for ac typesthat use screw type terminal blocks. The VisualKV Series is said to have the fastest processingspeed among products of this class. Minimumscan time is 140 ps and the minimum instruc-tion execution time is 0.7 ps. www.feeyence.comKeyence America

Small size, increasedperformanceThree new compact FieldPoint controllersdeliver increased performance, higher proces-sor speed, and significantly improved (10 timesbetter) Ethernet throughput, compared to theirpredecessors. The NI cPF-2220, cFP-2210,

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Mitsubishi ElectricAutomation Inc.

National Instruments

Baldor Electric

Opto 22

and cFP 2200 controllers include a 400 MHzPowerPC processor and Wind River VxWorksreal-time operating system for greater pro-cessing power and faster data analysis. ThecFP-2200 features up to 128 MB of SDRAMand onboard storage, and the cFP-2210 deÜv-ers up to 256 MB of SDRAM and up to 128MB of onboard storage. The cFP-2220 has dualEthernet ports for connectivity to enterpriseand dedicated I/O networks, as well as threeRS232 ports and one RS485 port for seria!devices. For logging and transferring data onexternal memory, the controller includes anadditional USB port and a removable Com-pactFlash slot. The cFP-2220 also has twicethe amount of onboard storage and SDRAM,up to 256 MB, for storing more data on thecontroller itself. Control engineers can cre-ate standalone embedded systems with thesenew controllers by using LabView Real-Time.www. ni.comNational Instruments

Modules make the controllerThe ELC Logic Controller is a reduced-sizePLC with 'an abundant module selection."The product line offers four controller styles,1-, 4-, 8-, 16- and 32-bit instructions, remotecommunication, easy connectivity to drivesand I/O, and built-in displays. This PLC isDIN rail mountable, allowing users to addas many modules as desired using snap-on/shde-into-place installation. Users canchoose from A, 8 or 16 I/O expansion mod-ules that are CE compliant, www.omega.comOmega Engineering Inc.

Drive control simplifiedThe NextMove elOO programmable controllerprovides 16 axis of interpolated motion andincludes an addressable range to manage upto 240 drives, I/O devices, gateways, and otherEthernet Powerlink devices. The drive axesprovide simple point-to-point motion, homingsequences, jog control, and torque demandfunctions. The device integrates managementof a real-time Ethernet network, which greatlysimplifies system design and installation. TheelOO uses a processor to deal with all com-munications requirements, leaving the maindigital signal processor to handle time-criti-cal motion tasks. The communications coreeven deals with message redirection wheremessages were not intended for this device(i.e., information from the USB port can beredirected to Ethernet devices). A field pro-grammable gate array core provides flex-ibility of design allowing firmware updates.

A user-selectable RS-485/RS 232 serial port isavailable; developers use the company's pro-prietary programming language. Mint, to cre-ate a simple interface to devices such as PLCs,text displays, and printers, www.baldor.comBaldor Electric

PLC connects the dotsSNAP-PAC-S2 is a standalone, multi-serial port,dual Ethernet interface programmable automa-tion controller. The controller has four serialports, each of which is fully configurable foreither RS-232 or RS-485 serial communicationfor cormecting to machines, devices, instru-mentation, I/O subsystems, and other equip-ment with serial interfaces such as weighscales, vibration monitors, RFID and barcodereaders, display terminals, and printers. AnRS-232 point-to-point protocol (PPP) modemconnection for communication over leasedlines, radios, and cellular networks is also sup-ported. The SNAP-PAC-S2 also features two10/100 Mbps Ethernet interfaces for host andI/O communication over Ethernet networks.These two independent interfaces can be usedto create dual Ethernet networks for segment-ing I/O and host traffic, or to design redun-dant Ethernet links for critical applications.www. opto2Z. comOpto 22

Compact, scalable PLC powerThe compact CPlL series of micro program-mable controllers delivers a scalable solutionfor automating small machines with as few as14 I/O points, with flexibility to expand to 180I/O points. It is said to offer faster processingspeeds than other micro controllers, and built-inpositioning capabihties. The CPlL series sharesthe same architecture as the CPIH, CJl, andCSl controller models, so programs are compat-ible for memory allocations and instructions.The CPlL supports IEC 61131-3 programmingvia CX-One Software that features time-savinglibraries of controls and function blocks thatsimplify program development, as well as onlineediting of program logic. A group of motion con-troi functions unique to CPlL establishes auto-matic communication with variable frequencydrives and servos without ladder programming.Simulation software included in CX-One allowspre-testing of programs without any hardwareand shortens commissioning time. The CPlLuses a standard USB port for programming andmonitoring, and offers up to two optional plug-in RS-232C and RS-422A/485 serial communica-tion ports. www.omTOn247.comOmron Electronics LLC

9O • SEfTEMBER 2OO8 CONTROL ENGINEERING • WWW.COntrOleng.com