Nano devices lead assault on traditional PLC applications

Programmable logic controllers, which are most commonly recognized as 15-128 I/O-point micro devices, 128-512 I/O-point medium devices, and over 512 I/O-point large devices, have come under pressure from still other manifestations of these devices over the past few years.

By Dick Johnson August 1, 2002
Trends In Programmable Logic Controllers
  • Network scalability

  • Ethernet communications

  • Built-in functionality

  • Increased features

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Programmable logic controllers, which are most commonly recognized as 15-128 I/O-point micro devices, 128-512 I/O-point medium devices, and over 512 I/O-point large devices, have come under pressure from still other manifestations of these devices over the past few years. To include the impact of these other technologies, the 2002 Control Engineering ‘s Programmable Logic Controllers Product Focus Study was expanded to include what is popularly called the nano PLC (under 15 I/O point), as well as PC-based control, software PLC, and embedded control devices. Even with the addition of these choices, market penetration of ‘standard’ units remained high and in the same order as the previous year’s survey.

Part of the reason for this can be traced to the most common industrial PLC applications. According to the survey, machine- and motion-control applications find primary use for these devices at the respondents’ facility. Traditionally, these types of operations require a greater volume of information at higher speeds than slower process/batch operations hence, more I/O points are necessary. According to Art Cambigue, product manager for Siemens Energy & Automation (Johnson City, Tenn.), ‘Medium- and large-size (128- 512 I/O points and greater) PLCs provide a great deal of flexibility. And with all PLCs getting cheaper it may be a long time before this installed base is changed.’

Small is good and getting better

Even without the flexibility of more I/O points and larger CPUs, small PLCs offer users advantages. Mr. Cambigue makes the point that the real difference between the relatively new nano devices and their higher capacity counterparts is that the small devices come with functions-often optional in larger units-already built in.

‘Functions built into these scaled-down units often include power supplies, high- speed counters, digital inputs and outputs, and communications. Additionally, they are much less expensive-in the $100 rather than the $1,000+ range. These low cost, lower I/O-count devices are especially suited to provide standardized control for machines built in limited quantities,’ Mr. Cambrigue adds.

Paul Ruland, plc product manager, AutomationDirect (Cumming, Ga.) concurs. ‘There is no doubt that the days of ‘control only’ PLCs are numbered, but there will always be applications for controlling small machines with only basic serial communication requirements. For such applications, low-cost, micro and nano PLCs fit the bill.

‘Micro and some of the powerful nano PLCs now offer increased features in the area of analog I/O points, PID, multiple communication ports, onboard display panels, and even device-level networking connectivity. For instance, a $99 PLC with four PID loops and two serial ports, matched with a $79 four-channel analog plug-in option card, is a cost-effective choice over traditional relays and a single-loop controller,’ Mr. Ruland continues.

Other low-cost options of the smaller PLCs include a memory cartridge with a real-time clock or a DeviceNet card, which can turn a nano PLC with inexpensive hardwired sensors into a flexible smart node capable of executing local logic. Other features including onboard displays and keypads allow machine operators and maintenance people an easy method for troubleshooting, without connecting a PC or other programming device. ‘Most often these integrated PLC display panels do not require separate programming software to configure and maintain,’ Ruland adds.

Bracing the ladder

Respondents to the survey also touted ladder logic as the programming method of choice for PLCs by a wide margin. But why, with at least seven other choices available, has ladder logic (probably the oldest language) held its popularity?

Joe Rubino, software product marketing manager for Omron Electronics LLC (Schaumburg, Ill.) explains, ‘One needs to consider the process and the majority of whom are responsible for creating and maintaining logic programs for PLCs. Not to over simplify, but the PLC and ladder logic were purposely made to be a direct descendant of hardwired relay logic.

‘Control engineers and technicians once responsible for building a hardwired control panel didn’t have to understand the ‘black box’ replacing the physical wiring and relays. Instead, they had to learn simple programming symbols that look like familiar coils and contacts, along with some rules about how to implement them in a ladder-logic program that looked very much like existing drawings for the hardwired control panel,’ Mr. Rubino says.

Over the years, basic features of PLCs and ladder logic have been enhanced as technology has advanced. Early users grew with and felt comfortable with those advancements. Many of those users remain in the current workforce, writing logic programs and supporting existing equipment that uses it. Carryover of ladder logic programming is a natural offshoot of this familiarity. Technicians also simply carry along the use of ladder logic as they transition from building wiring panels to PLC programming duty.

‘Conceptually, ladder logic is easy to teach vs. more advanced programming languages. Classes in ladder-logic programming are offered in most vocational institutions that produce a large percentage of technicians for the industrial control industry,’ Mr. Rubino adds.

Ladder logic capabilities can be augmented by the addition of other programming languages-function block is an example-to the mix. As PLC technology and the languages available to extend their capabilities continue to evolve, ladder logic may go the way of the original ‘programmable controller.’ I, for one, am not holding my breath.

Discrete sensors

To request information on these products, circle the following numbers in this issue or visit For more manufacturers of these products, visit the Control Engineering Buyers Guide at

Web capabilities expanded

Mayfield Heights, O.- Users of the Allen-Bradley PLC-5 product line can now more easily view, access, and manage process data as a result of the addition of new Web browser interface capabilities. Enhancements to the A- Ethernet PLC-5 controller line provide a built-in, HTML-based human machine interface for monitoring production and machine status via Microsoft Internet Explorer or other Web browser. The enhancements allow users to monitor PLC-5 data via a Web browser without having to create a Web page. Rockwell Automation Response Center

Micro PLCs feature new software, module

Alpharetta, Ga.- S7-200 Micro PLC now features Version 3.2 of its programming software, Simatic Step 7 Micro/WIN 32, and two S7-200 expansion modules (EM241 Modem Module and the EM253 Position Module). V3.2 adds configuration wizards for both modules, said to greatly speed the process of using a modem or configuring a motion profile. EM241 Modem Module expands the device’s functionality into remote communications. EM253 Position Module generates pulse trains used for open-loop control of speed and position for either stepper motors or servomotors. Siemens Energy & Automation, Inc.

Nano-controller offers flexible expansion, more

Schaumburg, Ill.- Omron’s new ZEN nano-controller’s compact size allows for installation in almost any location for a variety of simple control applications. The device, which measures 70 x 90 x 56 mm, features flexible expansion. Up to three I/O expansion modules can be added to any central processing unit for a maximum of 34 I/O points. The device’s processor can use its support software for ladder programming. Additionally, its software can be used for programming all parameter settings and printing. The LCD-type CPUs include eight operation buttons on the front panel to enable programming in ladder view. Omron Electronics LLC

Micro PLC addition

Cumming, Ga.- DL06 micro PLC has been added to the company’s Direct Logic line of programmable logic controllers. DL06 offers fixed models of 36 I/O points or up to 100 I/O points with expansion I/O. The device combines fixed I/O of 20 inputs and 16 outputs with four option card slots for expansion (discrete, analog, and communication modules), all in the same package. Other features include eight PID loops with built-in autotune capability and two communication ports for programming, as well as integrated high-speed inputs and pulse outputs and a built-in real-time clock/calendar. AutomationDirect

Real-time control and communication

Temecula, Ca.- SNAP-LCM4 is a powerful industrial controller that provides real-time control and communication to I/O systems, serial devices, motion controllers, and networks. The controller includes three serial ports and provides 10/100 Mbps Fast Ethernet and ArcNet communication options through four expansion slots. SNAP-LCM4 is designed to work with the FactoryFloor software suite and with all other SNAP products. Price is $1,895. Opto 22

Open-protocol Ethernet built into premium PLC

North Andover, Mass.- OEMs have a new value-adding option available in the new Modicon TSX Premium programmable logic controller from Schneider Electric. The new processor features a built-in Ethernet said to be the first in the industry that uses an open protocol. It offers direct connectivity to Modbus TCP/IP devices and a direct connection to Ethernet-enabled SCADA terminals or an end-user’s information infrastructure. With this PLC, end-users can readily connect factory-floor machinery to their business systems. This simple, plug-and-play advantage saves time and adds flexibility. The open protocol eliminates the need for a customized data collection server and simplifies connectivity between factory floor and business systems for IT managers. Schneider Electric

High-speed CPU for Series 90-30 PLCs

Charlottesville, Va .- New CPU374 for Series 90-30 PLC is said to offer significant speed and performance improvements for high-demand applications. The CPU374 features an AMDSC520 processor, running at 133 MHz, which is four to five times performance improvements over previous generation CPUs. In addition to high-speed processing, the device features a built-in Ethernet switch with two 10/100 Mbit ports. Its two CPU374 Ethernet ports share a single IP address, but are autosensing for data rate, duplicity, and cable crossover. CPU374 has a Boolean execution of 0.15 msec/K and 240 Kbytes of configurable memory. The controller supports up to 4,096 local and remote I/O points. GE Fanuc Automation

Flexible programmable controller

Germantown, Wis.- Wago Programmable Field Controller (PFC) combines the fieldbus coupler functionality with that of programmable logic controls. Users can now download simple logic control into each I/O node via the network or locally. Using IEC-61131-3 programming standards, programmers have access to all fieldbus and I/O data. The result is decentralized control that improves support for a PLC or PC. With the PFC, users can store and execute programs locally, while communicating I/O signals to and from the network. Program execution continues, even if the fieldbus connection is lost. The device is available for Ethernet, DeviceNet, Profibus, Modbus, CANopen, and Interbus, and is 100% compatible with the complete Wago I/O system. Wago Corp.

Gary Mintchell, Control Engineering, senior editor, also contributed.


Smallest and fastest PLC is class
Woodcliff Lake, NJ – Visual-KV is reportedly the first PLC with a built-in 2-color data window that permits the user not only to monitor PLC data, but to change programs and parameters in real time. At 2/3 the size of a conventional PLC, it is also said to be the smallest in its class.expansion I/O block can be placed up to 1-ft away with no loss of data speed. A handheld programmer is offered for transferring and saving ladder diagrams.

PLC is versatile, easy to configure
Vernon Hills, IL – Q-series PLC is designed so that up to four CPUs can be placed on a rack along with local I/O modules. Its platform competes with VME computers used in semiconductor manufacturing or combines process and sequential logic modules for batch control. Users can choose from a variety of sequential logic controllers, motion control modules, process control modules, and a PC module. Additionally, it supports open networks like Ethernet, Profibus, and DeviceNet, as well as Mitsubishi’s CCLink and Net/H.