PLCs are definitely changing. At the low end, in the sub-$1,000 price range, nano and micro-PLCs are gaining capability and offering lots of bang for the buck. At the high end, PLCs are becoming more like PCs every day. Sales are soaring and PLCs are here to stay.
Commenting on present market conditions, ARC Advisory Group (www.arcweb.com) says, "The industrial PC is not yet a threat," although they continue to hint at the faint possibility that somewhere, somehow, PCs will prevail. "Rapid changes in computing and communication technologies, a strong user acceptance of open systems, the global economic slowdown, and a small but growing threat from industrial PCs are combining to create turbulent market conditions and the threat of an uncertain future."
In spite of this doom and gloom attitude, ARC predicts that the total business worldwide for PLCs will increase from $5.8 billion in 2003 to $6.5 billion in 2006.
PLCs have certainly responded to ARC's "rapid changes in computing and communication technologies," and now fit right into open systems and networking. "One of the trends is that PLCs continue to have simplified programming," says Giardina. "You're seeing the continued expansion of programming languages and the simplicity of network setup."
Rockwell agrees that new opportunities are opening up. "One of the greatest opportunities for PLC growth is in safety control," says Miclot. "Today's safety PLCs are being utilized across a growing number of failsafe applications that were previously supported by safety relays. Safety PLCs can significantly reduce wiring costs and panel space as well as provide improved flexibility and reliability."
The PC-like capabilities of modern PLCs make some market researchers and suppliers want to change their name. "The term programmable automation controller (PAC) emerged to better describe a new breed of controllers that converge the best attributes of the PLC, DCS, PC, and open control platforms," says Miclot.
We continue to resist using that name to describe PLCs, but must admit that the nature of the PLC business has certainly changed. While nano and micro-PLCs continue to do traditional sequential logic work, their new capabilities let them compete in many other applications.
Higher-end PLCs are now doing tasks that once belonged exclusively to process control systems, such as DCSs. With their open PC architectures, PLCs are talking to business systems, such as ERP and asset management. And new PLCs are beginning to introduce even more capabilities, such as web servers, Ethernet communications, fieldbus connections, and HART.
You can see some of those new capabilities in the roundup products that follow:
BC, BX, CX, and IPC controllers all use TwinCAT programming software. The BC has a subset of PLC functionality, BX has standalone low-level PLC capabilities, CX can be used for mid to high-level PLC and motion tasks, and the IPC handles open PLC, motion, and HMI applications. BX and BC have choice of integrated fieldbus connections including DeviceNet, Profibus, and Ethernet.
Cigar Box Controller
The BX2 Motion-and-Machine Controller is about the size of a cigar box, yet it contains up to eight axes of control, up to six on-board drives supporting servos up to 1,600 W, and 46 onboard digital I/O points. The controllers' real-time operating system incorporates a comprehensive set of motion control functions. A syntax-free programming environment simplifies application development and tool integration. Built-in Ethernet supports controller networking up to 56 axes and a variety of external I/O expansion modules.
Berkeley Process Control
Ethernet I/O Kit
Remote I/O kits for DL205 and DL405 PLCs are available in three basic combinations to fit many Ethernet Remote I/O applications. A kit includes one H2-ERM Ethernet Remote Master module and up to 10 H2-EBC or T1H-EBC Terminator I/O Ethernet Base Controller modules, or one H4-ERM module and up to 10 T1H-EBC modules. Prices start at $369.
The TC7 Series of board-type PLCs is available in models as small as 90x60 mm. Each has eight inputs/outputs, two analog inputs, two thermistor inputs, and a control panel interface. The control panel interface allows for 7-segment LED outputs, single LED output, and a key switch input. Programming is in ladder language.
The 750-841 Programmable Fieldbus Controller has a 32-bit RISC processor, a 100-Mbps Ethernet port, and IEC-61131-3 and open architecture software interfaces and protocols. Programs are stored in flash memory. HTML pages can be placed on an internal server for use in web-based applications. It has a complete software suite that includes program editor, simulator, online debugger, and basic HMI software for a one-time site license under $1,000.
Graphic Display Control System
The Model 880 Network Control System serves as a host monitoring and control system for serial networks of gas detectors and other devices, including PLCs. It monitors 80 or more devices, displays device status and alarms on a 5.6-in. color touchscreen, and records device calibration, alarms, and other events to a 3.5-in. floppy disk.
MicroChem2 can be configured as transmitter, feedforward controller, or aeration basin controller. Up to three measurements can be connected in any combination of chlorine, chlorine dioxide, ozone, pH, ORP, temperature, and 4-20 mA. When used for oxygen control, it receives signals from up to three dissolved oxygen sensors, computes the average, verifies the correct functionality of the sensors, and applies a PID control algorithm on the averaged signal.
Severn Trent Services
The WebMaster GI industrial controller accepts four sensor inputs, including any combination of conductivity, pH, or ORP sensors. It also has eight analog inputs, nine digital inputs, four analog outputs, and eight relay outputs. ShoulderTap Server-On-Demand communications allows Internet access without permanent connections. It has user-friendly programming, allows multi-user access, and provides e-mail notifications for datalogs, alarms, and system summaries.