PLCs fight for future market share

The PLC industry finds itself the center of attention and controversy a lot lately. As technological competitor to the PC-based control market, PLC manufacturers are having to fend off the onslaught of PC-based developments with every bit of savvy and know-how they can muster. Certain software manufacturers have even gone so far as to predict the death of PLCs within five years.


The PLC industry finds itself the center of attention and controversy a lot lately. As technological competitor to the PC-based control market, PLC manufacturers are having to fend off the onslaught of PC-based developments with every bit of savvy and know-how they can muster. Certain software manufacturers have even gone so far as to predict the death of PLCs within five years. Conversely, talk to a few PLC manufacturers and they'll probably tell you their market will be strong well into the next decade.

It's hard to distinguish between fact and fiction with all the marketing hyperbole swirling overhead. Control Engineering turned to its readers for some straight information on the PLC market. Of the 1,500 CE readers polled for this study, 475 answered, resulting in a 32% response rate. Nearly all that responded, 97%, qualified by stating they recommend, specify, and/or buy PLCs.

What does the I/O control?

For this study, PLCs are categorized into three sizes depending upon the number of I/O points they're equipped to handle: micro (up to 128 I/O points), medium (128-512 I/O points), and large (more than 512 I/O points). Because many of the respondents indicate they use PLCs in several combinations, results exceeded 100% when the survey asked what types of PLCs respondents use.

The trend favors the smaller sizes. Micro PLCs are the current preference, being used in 80% of respondents' applications. Medium-sized PLCs followed with 71.3% of the tallies, while large PLCs are being used by 41.9% of the respondents.

What are the major applications of PLCs at respondents' plant sites? Since respondents are asked to control several types of applications, responses again exceed 100%. As one might guess, machine control, the type of application PLCs were specifically developed for, tops the list. Eighty percent of respondents use PLCs for machine control.

Perhaps a bit unusual were the next two most popular choices. Sixty-eight percent of respondents use PLCs for process control, a segment of the industry PLC manufacturers have only found success with in the last decade. Thirty-nine percent use PLCs for motion control, an application where widespread incorporation of PLCs has been traditionally difficult. Batching, a subset of process control, was next with 34% of the responses.

Bill Black, business leader of micro, nano, and Operator Control Station (OCS) products for GE Fanuc (Charlottesville, Va.), says the reason more users turn to PLCs for motion and process control is the proliferation of specialized software tools that have eased integrating PLCs with these applications. 'With process control, PID has been included into the instruction set and C programming has been added, which better suits process control than traditional ladder logic.' For motion control, Mr. Black says features such as ramping, homing, accel/decel, and servo/stepper modules have all been incorporated into PLC function. GE Fanuc's new Mini OCS PLC can be used in both cases, possessing an instruction set that includes PID and motion commands.

When asked what primary end product each respondent's company is responsible for, raw materials processing is the most popular response by a two-to-one margin over manufacturers of machinery and equipment for manufacturing and service industries. The two combined for a 75% share of the total votes. Also on the list were makers of instrumentation and control equipment (7.1%); automotive and other transportation equipment manufacturers (5%); and other fabricated metal and miscellaneous manufacturers (3.7%).

Communication and programming

How are PLCs interfacing with other control systems? Nearly half (49%) aren't interfacing with anything, continuing to operate in stand-alone mode. Thirty-one percent of respondents network with other PLCs, 27% network with PCs, and 21% network with DCSs.

For networked PLCs, Allen-Bradley's Data Highway+, is used by 44%. Following closely in second, with 40.8% of the responses is Ethernet. Modbus is third on the list with 24%, and DeviceNet is fourth with 12.5%. Other protocols used are ControlNet, Profibus DP, and Interbus.

To program PLCs, an overwhelming 95% of the respondents use ladder diagrams. Seventeen percent of the respondents use function block diagramming, while 9% use sequential function chart.

Future PLC plans

Connectivity is a primary concern for PLC users as they look at future control issues. When asked what their plans call for, PLCs with more remote I/O subsystems topped our respondents' wish list with 41%. Next is having PLCs with more plug-in I/O modules, gathering 37% of responses. After connectivity, 29% say they want to get smaller by installing micro PLCs.

Jeff Meyers, product marketing manager for Omron Electronics (Schaumburg, Ill.), doesn't expect wholesale replacement of PLCs by PCs anytime soon, and says we only need look to the decade or so it took for the industry to accept PLCs over relays. The question of reliability is a major concern, he says. 'I barely go a week without a glitch on the computer in my office. Computer glitches mean downtime, and downtime means money.' Mr. Meyers says the industry may be moving toward a hybrid type of controller; one that combines computers' ability to control complex applications with the reliability of PLCs.

Survey responses indicate PLC purchases will be at or near break-even level in the next 12 months. Forty-three percent indicate their purchases will remain the same in the next year; 27% say their companies purchases will increase, while 10% say purchases will decrease. Seventeen percent are uncertain and 4% had no answer.

Marketing rhetoric over the PLC vs. PC debate will undoubtedly continue for quite some time, with representatives on both sides making valid arguments. Size of the PLC may be shrinking, but it's importance to the control industry still looms large.

PLC products

For more information on PLC products, visit

Small application controller

Charlottesville, Va.- Mini OCS is designed for control applications with less than 28 I/O. It combines a logic controller, operator interface, and optional networking (CsCAN or DeviceNet slave) in an integrated package. A variety of discrete, analog, and motion I/O options are available. The Mini OCS features an instruction set that includes floating point math, PID, motion commands, and data manipulation. Nine built-in I/O configurations are available. The accompanying Cscape software combines IEC 61131-compliant ladder diagram programming with networking and operator interface messaging for complete OCS integration. The compact enclosure is NEMA 4/12 rated for corrosive environments and those subject to washdowns. GE Fanuc

Fault tolerant controller

Alpharetta, Ga.- Siemens Energy and Automation's Simatic S7-400H redundant controller is a fault-tolerant version of its Simatic S7-400 PLC that offers active redundancy for mission-critical applications. The S7-400H is configured as two S7-400 PLCs sharing a common or separate backplane operating in parallel, hot back-up mode. In case of a fault, a bumpless changeover occurs between the affected and standby unit without any lost data. A program written for nonredundant systems using the Simatic Step 7 tools environment can be easily ported to the redundant system, and vice versa, with a simple option package. Once programming is complete, both CPUs are automatically updated. Siemens E&A


Vernon Hills, Ill.- Alpha Series compact controller family's distinguishing characteristics are its small size (2.8 in. 3 3.5 in. 3 2.2 in.) a real-time clock with scheduling functions, and a wide range of control functions. Included is icon-based programming technology, with drag-and-drop construction techniques; a function block control tool, which requires no knowledge of ladder logic programming; and a built-in operator interface used for on-the-unit programming and for display of messages and data. Alpha Series controllers have high-current output circuits that switch 10 A; analog/digital ability on the same input channels; a wide range of units, with up to 30 I/O points to fit application requirements; and offline system simulation to detect design faults before startup. Mitsubishi Electric Automation

Controller with break-neck speed

Schaumburg, Ill.- The CS1 PLC possesses a processing time of 0.04 msec per basic instruction, a program memory of up to 250K, up to 5,120 I/O points, and FlashRAM storage of up to 30 MB. Nine different CPUs are available for a range of applications, from small-scale systems to very large, fully-integrated networks. The CS1 provides a variety of proprietary and open networking capabilities including Ethernet, Profibus DP, DeviceNet, and Omron's own ControllerLink network that allows peer-to-peer, PLC-to-PLC or PLC-to-PC communications. Omron's new CX-Programmer software features a unified Microsoft Windows-based development environment is said to simplify program design and development. Omron

Modular mid-size PLC

Sunnyvale, Calif.- FA3S is a mid-sized PLC for applications requiring up to 256 I/O points. To save time, the unit includes more than 120 instructions including proportional scaling, step/subroutine, and annunciation commands. Special modules are available for data communication, fiber-optic remote I/O connections, and interrupt processing. Users can customize the FA3S to fit their applications with such features as four different CPUs, 1 to 8K program memory, built-in ASCII communications, and 0.3 ms/K boolean scan. The I/O mounting system allows users to build chassis that are the right width. Users can also mount local I/O points up to 30 ft from the CPU with plug-in cables. IDEC

PLC breaks price barrier

Cumming, Ga.- The DL05 micro PLC is said to be the first micro PLC to break the $100 price barrier while retaining the functionality of many higher-priced PLCs. The DL05 offers a removable connector, reducing downtime by allowing users to prewire connections. Also offered are eight inputs and six outputs; diagnostic and communications LEDs; and Microsoft Windows-based programming capability. Either surface or DIN-rail mountable, the DL05 has a 4.75 3 3.75 3 2.5 in. footprint. Six versions are available, including ac/dc input and output, and relay ouptput types. Two built-in RS-232 ports can communicate with operator interface devices such as operator panels, programming devices, and other PLCs. The second port is addressable, so the DL05 can be a station on a network of intelligent devices. This company formerly was PLCDirect.

Software expands functionality

Mayfield Heights, O.- Rockwell Automation has released version 2.10 of its Rockwell Software RSLogix 5000 PLC programming software. It supports the Allen-Bradley ControlLogix architectures and the Logix5500 processor, is based on IEC 1131-3 standards, and has features to decrease development and debug time. Users can also merge data with other applications and integrate with third-party Microsoft-based software. Additions such as data descriptors and search/replace functions improve the overall capabilities of the ControlLogix system. Version 2.10's Program Upload Merge feature allows users to upload controller data, merge it into an application database file, and resynchronize code. The ladder diagram editor and tag editor have been enhanced to allow for monitoring and changing the forced I/O status. Rockwell Automation

Adapter converts I/O to PLC

North Andover, Mass.- Schneider Electric extends the reach of its Momentum line of distributed I/O and Processors with the introduction of the new M1 512K Processor Adapter. With more speed, memory and features, Momentum can now tackle even more intensive process applications. The M1 512K Processor Adapter snaps onto a Momentum I/O base to form a traditional micro/nano-class PLC. I/O can then be extended via the I/OBus port to additional Momentum I/O modules. The new XMIT built-in instruction extends the communication capabilities to other RS-232 and RS-485 devices. With over 24,000 words of user storage, scan times under a millisecond, and up to 8,192 I/O, the M1 512K Processor Adapters, coupled with I/O Bases and Option Adapters, provide a solution for data intensive applications. The adapters include a version (171 CCC 780 10) with two serial ports; one dedicated RS-232 port and the other dedicated RS-485 port capable of single master or multi-master communications. The other M1 512K Processor Adapter (171 CCC 760 10) also has a dedicated RS-232 port and an I/O Bus port. Schneider Electric

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