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.