Research on Programmable Logic Controllers

Nothing takes the fun out of a control engineering project faster than having to wade through piles of vendor and/or supply house catalogs to find the components for a control system. Even small machine control applications require a lot of specifying, recommending, and purchasing of parts for the simplest of control logic systems—especially if it is to be rendered in traditional relay la...

By Dick Johnson, Control Engineering December 1, 2007

Nothing takes the fun out of a control engineering project faster than having to wade through piles of vendor and/or supply house catalogs to find the components for a control system. Even small machine control applications require a lot of specifying, recommending, and purchasing of parts for the simplest of control logic systems—especially if it is to be rendered in traditional relay ladder logic. Relays, relay bases, timers, limit switches, wire, wire ductwork, pilot lights, pushbuttons, etc. and—last but not least—an enclosure to put them in are just a part of the “stuff” needed to get the project off the ground.

Enter the programmable logic controller (PLC) and its successor, the programmable automation controller (PAC). These items represent “one stop shopping’ for a wide variety and size of machine control applications. According to this year’s Control Engineering survey, suppliers have risen to the occasion again to make sure that control engineers have what they need to do the job—simply, cheaply, and effectively.

In the most recent survey, done in conjunction with Reed Research, 548 respondents made it clear that the modern PLC has met their expectations. Of these, 57% uses PLCs for in-plant requirements and 22% use them for OEM (resale) applications. The remaining 21% buy and use them for both. The types of PLCs in use for these applications vary greatly in the number of I/O points they handle. The breakdown of “type” indicates that control engineers are using mostly microPLCs—those that can handle from 15 to 128 I/O points. These account for 38.7% of PLCs in use. Medium-sized PLCs, those servicing 128 to 512 I/O points, followed at 32.7%, and large PLCs handling greater than 512 I/O points accounted for 18.4%. The least used was the nanoPLCs handling less than 15 I/O points, at 10.4%. Overall, PLCs handling between 15 and 512 I/O points accounted for nearly three-quarters of all the devices sold.

What of the probable successor to the PLC, the programmable automation controller (PAC)? In last year’s survey, fully 44% of users were considering using these ruggedized PCs in a PLC form factor. Even with the PACs’ greatly enhanced capabilities, this year the number of control engineers considering their use fell to 31%. In all likelihood, control engineers were considering using PACs in new or upgraded applications. Of the respondents reporting that they will use PACs in the future, most (75%) reported using them to supplement their use of PLCs. The remainder said they would use them to replace PLCs.

Networking options

The major applications of PLCs cut a wide swath through the automation world. As expected, machine control (82%) is still the most popular application. Process control (74%), motion control (55%), batch control (31%), and diagnostic applications (25%) follow. The smallest use of PLCs was reported in safety applications (1%).

Methods of interfacing with other control systems are key to the flexibility of the modern PLC. According to respondents, interfacing with a network is the primary application for PLCs in use (69%), with the remaining 31% used as standalone devices. Of those devices used in a network, most were used with personal computers or PACs. An equal amount networked with other PLCs. The smallest amount, a little over 5% of the total networked units, was mated with distributed control systems.

PLC networking protocols also provide almost unlimited flexibility to the control engineer. Although there were clear favorites such as Ethernet, Serial RS-232/RS-485, and 4-20 mA in that order, the list of networking protocols used was long and varied. Following the three front runners are, in order of popularity,:

  • DeviceNet

  • Allen-Bradley Remote I/O

  • Modbus

  • ControlNet

  • Wireless protocol

  • Profibus

  • HART.

PLC programming language has remained flexible as well, but the survey reflects clear favorites among the choices. Ladder diagram (96%) and function block (50%) programming methods are at the top of the list. They have remained there in that order since 2005 (see accompanying chart). Clearly, ladder diagram programming will be hard to dislodge from the top spot, given its commanding lead, but function block programming has made progress over the past couple of years. Structured text has made a strong showing by moving from sixth place in 2005 at 13% to third place in 2007 at 24%. The big loser was C programming, which fell from a clear fourth place in 2005 to sixth this year. Instruction list programming was not far behind with a fall from fifth to seventh place in the same time period.

The PLC selection process is never an easy one. However, there were a number of features tagged as very important when specifying, recommending, and/or buying a PLC. According to the respondents to the survey, built-in communication support ranked number one on their hit parade. Other attributes, ranked in descending order, include: PID capability, fast scan time, total memory capability, motion support capability, a removable memory cartridge, and wireless capability.

Do control engineers think they are getting what they need from their PLC suppliers? Satisfied customers accounted for 95% of those responding, leaving only 5% with complaints that would affect their future purchasing decisions. Two very simple comments from many survey respondents summed up respondents’ feelings about the PLC selection process. To these front-line engineers, “standardization” and “not buying more complicated PLCs than needed” are key criteria in the selection process.

What to look for when you buy

Despite the fact that 53% of those responding projected that their PLC purchases would remain the same over the next year, the market still seems healthy. Industrial purchasing has remained robust of late and 38% of those reporting predicted that their PLC purchases would increase in the future (over the next 12 months). And what available features are expected to be specified in these future purchases? Features deemed very important are listed below in descending order:

  • Universal programming software for multiple hardware platforms

  • PLCs with more remote I/O subsystems

  • PLCs with integrated I/O modules

  • PLC I/O networked to PCs

  • Redundant processors and I/O

  • Micro PLCs

  • Web-enabled PLCs that include e-mail/phone notification and alarming

  • PLCs with PC processors onboard

  • Nano PLCs

  • Rugged PC controllers with soft logic software

  • Handheld setup tools.

In fact, the availability and importance of the number one feature on the above list was echoed many times in a survey question soliciting advice about choosing PLCs. “ Don’t sweat trying to find the lowest cost hardware; retraining in programming software will eat up any savings. Pick a couple of vendors and stick with them” was a typical response.

Another control engineer volunteered, “It’s the programming software. Differences between vendors on usability of the programming software are a bigger differentiator than hardware features.” Finally, several respondents summed it up, “A standardized programming language is an absolute need.” In any case, a wish list like this certainly gives PLC/PAC developers something to focus on.

PLC products

Responding to the survey using a list provided, Control Engineering subscribers identified the following vendors as leading suppliers of PLCs. Representative products from these vendors are shown. Additional survey data that encompasses additional user questions, verbatim comments, and 25 more vendors of PLCs can be found online in the research report, available through the Control Engineering Resource Center. Search “PLCs” at to find recent News and New Product reports as well.

More products, vendors

The following vendors were also covered in the product research study. Search “PLC” atop to find the research report in the Resource Center, and additional product descriptions in the Archive and New Products sections.

  • ABB (Bristol Babcock)

  • Advanced Micro Controls

  • B&R Industrial Automation

  • Baldor Electric

  • Beckhoff Automation

  • BoschRexroth

  • Control Technology Corp.

  • Eaton (Cutler-Hammer)

  • Emerson Process Management

  • Fuji Electric

  • Hitachi

  • IDEC

  • Keyence

  • Mitsubishi Electronics

  • Moeller Electric

  • National Instruments

  • Omega Engineering

  • Omron Electronics

  • Opto 22

  • Panasonic Electric Works

  • Phoenix Contact (Entivity)

  • Toshiba

  • Wago

  • Yaskawa Electric

  • Yokogawa

Flexibility, standardization
For machine builders looking to standardize on a single integrated control platform with multi-disciplined capabilities, the Allen-Bradley CompactLogix L45 controller offers expanded scalability and integrated motion control capabilities. Controlling up to eight axes of motion, the L45 is an extension of the Logix Control Platform, which brought integrated motion and distributed control capabilities to these smaller applications. The platform leverages the same control engine, development tools, network and operator interface technologies, and communications services throughout, making it fully integrated and scalable for use in discrete, motion, batch/process control, safety, and drive applications.
Rockwell Automation

High resolution modules

AutomationDirect has extended its line of DirectLogic option modules to include 16-bit high-resolution analog modules designed for the DL05 and DL06 PLCs. The F0-08ADH-1 eight-channel current input module operates with a 0-20 mA input range. The F0-08ADH-2 has jumper selectable input ranges of either 0-5 Vdc or 0-10 Vdc The four-channel F0-04DAH-1 and eight-channel F0-08DAH-1 current output modules provide a 4-20 mA output range, while the four-channel F0-04DAH-2 and the eight-channel F0-08DAH-2 output modules provide a 0-10 Vdc output range. Prices start at $129 for the F0-08ADH-1 module.

Field mountable, distributed
According to Siemens Energy & Automation, cabinet-free, distributed intelligence over Ethernet is available at the field level for the first time from Simatic ET200pro CPU. The unit’s IP-65/67 rating allows the controller to be machine-mounted, relieving the central CPU by shifting intelligence to the field level, and to perform in washdown applications or under dirty conditions over a wide temperature range. It includes multiple onboard networking capabilities including a combined MPI/Profibus-DP connection and an Ethernet connection with a built-in three port switch. In addition to acting as a Profibus-DP master/slave, the CPU supports the Profinet industrial standard via the built in Ethernet port, enabling enhanced Ethernet features such as operation as a deterministic, real-time I/O controller.
Siemens Energy & Automation

PACs added to line of PLCs
The Modicon PLC line, which began in 1968, now offers the Modicon M340 PAC, a platform that offers communication, motion, database, and manipulation capabilities in multiple programming environments. The M340 family simplifies setup and implementation by standardizing on a single programming tool: Unity Pro IEC 61131-3 development software. Offering a choice of five IEC languages, graphic programming, and advanced online help, the M340 also enables fast execution of both Boolean processing and floating decimal calculations. It has 4MB of internal memory (upgradeable to 16MB), 256KB data, and can manage applications with up to 70K instructions.
Schneider Electric

Low maintenance micro control

The new VersaMax Micro 64 system from GE Fanuc Automation is part of the company’s VersaMax Micro line of controllers. The Micro 64 is designed to minimize maintenance cost. A user-friendly memory module that can be connected to the controller to download program changes without the need for a PC. Its Proficy Machine Edition Logic Developer PDA software allows users to interface a Palm handheld device to monitor/change data, view diagnostics, force on/off, and configure machine setup. The Micro 64 meets global standards and is supported internationally with GE Fanuc Automation sales offices and distribution.
GE Fanuc Automation

Online Extra Also read, from Control Engineering:

Advanced, capable compact logic controller
The newly introduced FX3U Series of next-generation SuperMicro programmable logic controllers are said to offer unmatched execution speed, performance-enhancing instructions, and unparalleled connectivity. Ideal for machine control applications, the FX3U delivers faster throughput, larger memory (800 per cent more than the previous series), improved motion integration, and broader network connectivity. Unlike rack-based platforms that have separate power supplies, CPUs, and input/out modules, the FX3U compact PLC integrates all of these components in a single platform. It also features what is said to be the most memory and fastest instruction processing time of any PLC in its class, and is the only compact PLC with a Profibus Master and a high-speed fiber optic networking card for servo amplifier control. The FX3U also features left- and right-hand buses for communication, analog I/O, and high-speed input and high-speed output modules, which further increases system flexibility and application opportunities.
Mitsubishi Electric Automation

Shrink that control panel

The KV-300 Series programmable logic controller from Keyence America is one-third the volume of conventional units and requires only one-half the footprint. Control panels using these units are smaller and wiring space is significantly reduced. Even at the maximum I/O configuration, a control panel contains no more than 13 compact modules. The proprietary modular design allows easy DIN-rail mounting and employs a quick disconnect lock mechanism. No additional rack or base is required when extending the system configuration. A single computer running its developer’s Ladder Builder software can communicate with multiple CPUs to edit programs, monitor operations, or monitor a CPU while communication with another computer. The KV Quick Scan method controls all I/Os with a fast 0.5-ms scan time, which is said to overcome the scan time delays of conventional wire saving systems.
Keyence America

Near and remote I/O
Compact FieldPoint is an easy-to-use, highly expandable programmable automation controller composed of rugged I/O modules and intelligent communication interfaces. Users can download their National Instruments’ LabView application to the embedded controller for reliable, stand-alone operation and connect their sensors directly to high-accuracy analog and discrete I/O modules. These industrial I/O modules filter, calibrate, and scale raw sensor signals to engineering units and perform self-diagnostics to look for problems, such as an open thermocouple. Compact FieldPoint network communication interfaces automatically publish measurements with an Ethernet network. Users can access I/O points nearby or miles away on the network using the same simple read/write software framework.
National Instruments

Feature rich programmable logic controllers

The ELC Logic Controller from Omega Engineering Inc. is the latest technologically advanced PLC (Programmable Logic Controller) in the PLC market. This reduced-size ELC has an abundant module selection that provides a “just right” concept for delivering only what users need at an economical price. It also offers a wealth of features including four controller styles, 1-, 4-, 8-, 16- and 32-bit instructions, remote communication, easy connectivity to drives and I/O modules, and aes to suit their  PLC needs. This module is said to be ideally suited for any industrial or manufacturing environment and is CE compliant. Price starts at $93.

Omega Engineering Inc.

Power, flexibility in motion control

Baldor’s MintDrive-II is said to offer the best in flexibility; integrating a powerful motion controller and positioner, and an ac servo drive into a compact package. The MintDrive is a single-axis positioner that can handle motion, PLC, and HMI tasks easily according to its developer. Programmable in Baldor’s multitasking Mint software that provides support for move types such as indexing, CAM profiling, electronic gearing, flying shears, and speed control. Included is a table drive PLC task for user-defined operations and is provided as an easy interface to an external device such as a PLC.

Baldor Electric Inc.

Micro New standalone pac introduced

The Snap-PAC-S2 is a standalone programmable automation controller and the newest addition to its developer’s Snap PAC System. The Snap-PAC-S2 has four serial ports, each fully configurable for either RS-232 or RS-485 serial communication, which are said to make it ideal for connecting to machines, instrumentation, I/O subsystems, and other equipment with serial interfaces. Well-suited for deployment in any of its developer’s distributed control system architecture, the Snap-PAC-S2 also features two 10/100 Mbps Ethernet interfaces for host and I/O communication over Ethernet networks. These two interfaces can be used to create dual networks for segmenting I/O and host traffic, or to design redundant Ethernet links. Other features include a 32-bit multitasking processor with floating point unit, 32 MB of RAM, 16 MB of flash memory, and 8 MB of battery-backed RAM. The controller supports multiple communication protocols, including TCP/IP, SNMP, FTP, Modbus/TCP and OptoMMP, and is capable of multitasking up to 32 control programs simultaneously.

Opto 22

Micro programmable controller

Omron’s CP1L programmable controllers deliver a scalable, economical solution for automating small machines with as few as 14 I/O points but with flexibility to expand to 160 I/O. The controllers come with 14, 20, 30, or 40 I/O modules built-in. All models support positioning and motion control with four high-speed encoder inputs (100 kHz) for counters that use two-axis differential phase control or four axes of single-phase control, and two high-speed pulse outputs (100 kHz) for two-axis control. The CP1L uses a standard USB port for programming and monitoring and offers up to two optional plug-in RS-232C and RS-422A/485 serial communication ports. IEC 61131-3 programming for CP1L is supported via CX-One Software that features time saving libraries of Omron controls and function blocks that simplify program development as well as on-line editing of program logic. Simulation software included in CX-One allows pre-testing of programs without any hardware and shortens commissioning time.
Omron Electronics LLC