The beginning of a sweeping change is upon the control and instrumentation world. With the availability of robust hardware, open technology and real-time, Windows-based operating systems, PC-based control is emerging as a new control paradigm for increasing manufacturing productivity. PC-based control offers open and more intuitive traditional solutions at a lower total system cost and easier migration to future technologies. Easier development, integration, portability, and access ensure a flexible and efficient solution.
Industry analysts and major global manufacturers agree that PC-based control is the future. Today, more than 20 vendors offer PC-based control as an integral part of industrial automation product lines. The number continues to grow as industry leaders include PC-based solutions. It is important to understand PC-based control and, more importantly, the benefits and challenges accrued when committing to this next level of control technology.
Manufacturers around the world look to PCs to play a bigger role in their control systems. PCs are already an accepted platform for system supervisory control, monitoring and reporting, as well as off-line data management and analysis. Manufacturers have already realized the flexibility of the PC and the easy-to-use open architecture of Windows-based software applications for the manufacturing environment.
Now, with the advent of Windows NT v4.0 and the continued price erosion and performance increases of industrial PCs, industrial control is poised to move from an expensive proprietary hardware base to one with a foundation of PC-based software. Most of the leading experts agree that PCs are the control platform of the future.
What is PC-based control?
PC-based control replaces the traditional and proprietary controllers such as programmable logic controllers with standard PC-based hardware and software. PC-based control runs on personal or industrial hardened computers and provides answers to initiatives for lean control programs. Machine control programs with PC-based control experience maximum control with the minimum hardware configuration. This approach provides end-users and machine builders with a platform to dramatically reduce control system design time and maintenance costs by reducing downtime with built-in diagnostics, real-time simulation, and consolidation of data into a single database.
The evolution of control
The industrial control market is at an evolutionary point. Much like the emergence of relay logic in the early 60s, the introduction of PLCs in the early 70s, and the MMI/SCADA in the mid 80s, PC-based control is ready for rapid growth and acceptance. Like other new technologies, resistance to PC-based control was strong at first but is fading quickly as users realize the benefits of faster throughput and lower production costs. The entrance of larger, substantial vendors and the adoption of this technology by the large automotive companies signifies the growing acceptance and first step in the evolution of this technology.
The PC and desktop software industries are also driving this evolution. Windows NT version 4.0 is the first Windows-based operating system that provides a truly deterministic, hard real-time operating system. According to Microsoft, a hard real-time operating system is one "that must, without fail, provide a response to some kind of event within a specified time window. The response must be predictable and independent of other activities undertaken by the operating system." This critical timing and reaction required for a PC-based control system was lacking in the past and only recently became available through standard third-party extensions.
The availability of low-cost Pentium and Pentium Pro processors also fuel this evolution. PCs are continuing to increase in power and decrease in price. Performance continues to double every 8 to 14 months. This rapid development provides immediate performance benefits to PC-based control systems. In comparison, standard PLC performance doubles about every 4 to 6 years.
As with all evolutions in this industry, end-user market demands and competition drive the developments. Manufacturers require control systems to be easier to implement, maintain, and use if internal engineering resources are to focus on core values. Reduced cost of manufacturing, increased productivity, shorter time to market are additional factors driving manufacturers to adopt new technology and control paradigms.
Make no mistake. The evolution is occurring! Some estimates indicate the PC-based control market is growing at a rate of over 70 percent a year!
PLC versus PC
To fully understand the PC-based control technology, first examine the traditional method and de facto standard of control systems today--the PLC. There are strong arguments for PLC-based control systems. The PLC was designed and developed for industrial applications. One reason for the slow acceptance of higher level technology is that PLCs use an architecture proven over 25 years. There is a strong base of vendors. These vendors are large and have a strong global infrastructure for support and service. Lastly, PLCs dominate the plant floor today. With PLCs, there is no fear of change.
However, there are some strong disadvantages to the PLC-based control systems. PLCs processors, operating systems, programming languages, I/O, and networks are proprietary. Developing and maintaining these systems requires specialized training and knowledge.
Manufacturers using multiple vendors must train engineers and maintenance personnel in multiple systems. Interconnecting the I/O of multiple vendors is often difficult or impossible. The hardware is proprietary. It requires one to stock costly back-up units and spares. This often involves single source procurement. Many PLC systems require a separate PC for programming, process monitoring, and supervisory control.
The PLC is fundamentally a box or computer with a processor. This processor runs an operating system. The operating system runs an application. The application executes control logic. At a fundamental level, PLCs and PCs are boxes with a processor that runs an operating system to support applications. A PLC is fundamentally a PC.
Then why the hesitation and concerns with PC-based control systems? One often stated reason is the low reliability of a PC. But this is a specious argument considering the rapid development of desktop and industrial PCs. For decades they have been used in industrial environments. Hardened and fault-tolerant models are available for extremely harsh environments. Windows-based operating systems run PCs using redundant hard drivers, back-up power supplies, multi-processors, and multi-threaded applications. Windows NT offers the reliability and security required for mission-critical applications.
Furthermore, in the PC industry development and price erosion occurs at a much quicker pace. Historically, PCs have far out-paced PLCs in performance and cost. A hardened, fault-tolerant PC for industrial applications is the most cost-effective control system solution today.
The benefits of PC-based control
An industrial computer running Windows NT as a PC-based system adds many features and flexibility to a control system. It drastically reduces the cost of ownership of a control system by making controls easier to use, reducing design and implementation times, improving diagnostics, increasing performance, and easing integration with other hardware and software applications. Most importantly, it future proofs your system for easy improvements and growth.
One box rather than two
A common configuration for a PLC-based control system includes a PLC for logic and control of the process or system and a PC for monitoring, supervisory control, and other required data management activities. PC-based control offers a single PC to provide the functionality of both the MMI/SCADA PC and the PLC.
Automation Research Corporation, a large industrial control research corporation, states "If you currently use or plan to use PC-based MMIs, you will be able to realize the immediate cost benefits from hardware integration when adopting PC-based control that runs in the same box."
This is not a trivial benefit. Now end-users as well as machine manufacturers realize an immediate saving while implementing the latest technology. Often, manufacturers must choose between lower cost and technology. PC-based control provides a unique opportunity to choose both.
PC-based control reduces hardware costs up to 44 percent and software development time of up to 50 percent. This is because of the flexibility, open architecture, a choice of I/O, processors, networks, and memory that are available. Furthermore, most industrial and hardened PCs support standard memory, network, and other components allowing for cost-effective implementations and upgrades. Hardware can be selected based on the application rather than the availability of components from vendors. Manufacturers are no longer confined or limited to a single vendor.
Lower integration costs are an additional benefit of a PC-based control system. Many PC-based control vendors offer an integrated MMI/SCADA and PC-based control package. A single tag definition and database configuration for both control and monitoring saves development and maintenance time and reduces the opportunity for human errors.
In addition, functionality such as graphics, trending, and alarming are already tightly integrated in an off-the-shelf package. More efficient and productive programming resulting from international standards also contribute to a lower integration cost.
User developed control programs and modules are much more component- and object-based allowing for a modular approach. This simplifies re-use of programs, graphics, logic, and the like. A standard such as IEC1131-3 allows programmers to develop in five languages and leverage experience in standard ladder programming as well as benefit from the ease of use of new graphical languages. A single box also requires less physical integration such as wiring and installation.
PC-based control allows for simulation of process and system design on the PC before implementation, a task that is often difficult or impossible on a PLC. Programs can be developed and tested before connecting to equipment or I/O. This functionality also can be used when choosing I/O. The user can actually build the entire control project before choosing or mixing and matching I/O to real-world devices.
One can view performance and machine responses on the PC without risking damage to the process or machine. You can diagnose problems and make the proper adjustments in the software before implementing it in the hardware. In addition, new design concepts can be safely tested. Operators use PCs for system training. This flexibility contributes to reduced project implementation time and risk that translates into savings for the end-user or machine builder without sacrificing technology.
Don't overlooked performance when comparing PC- and PLC-based control systems. PC-based control offers response times of better than 100 microsecond in a deterministic, hard real-time control environment. Adding a quicker processor or additional memory achieves even better performance. Keep in mind that increasing the performance is a standard activity with a PC, something that is impossible with most PLC systems.
Finally, PC-based control systems are easier to upgrade and grow. Typically, it is maintenance issues rather than performance enhancements that drive PLC system upgrading. A system may increase the number of stations on a network or number of I/O points, but the controller cannot improve unless it is replaced. Alternatively, improvements and upgrades to PCs are simple and cost effective. Users realize immediate improvements and can perform the upgrades with out costly third-parties.
The benefits of PC-based control systems far outnumber the challenges. The future enhancements and proliferation should only make the argument for PC-based control stronger. Fueled by the enormous developments in the PC market and customized for the control industry by the dominant control system software and hardware vendors, PC-based control is sure to have a quick adoption rate. Already, many large multinational manufacturers are using and adopting this technology.
However the technologies can help manufacturers and machine builders of every size realize immediate returns in their automation investments with an increase in technology and competitiveness. Of course, with any new technology, it is important to select a strong vendor to insure a smooth and successful implementation. Select an industry leader with software experience as well as a global infrastructure for support and service.
By the turn of the century, the PC-based solution will be the standard for control systems. The proprietary hardware and software used today, will no longer be a viable or competitive solution.