Overview

Industrial process control has its roots in the big process industries, sometimes called the Four P's: paper, petrochemicals, paint, and pharmaceuticals. These plants are characterized by having thousands of instruments measuring such variables as pressure, temperature, flow, and level, plus hundreds of control elements such as valves, pumps, and heaters. They use a great deal of automatic control, including feedback, sequencing, interlocking, and recipe-driven schemes. Modern control systems for these plants are, as you might imagine, very complex and very expensive. Most large process control systems are designed and installed through cooperative efforts between manufacturers, system integrators, and the customer's control engineering staff. These are the Big Guns of process control.

Chances are that you are probably faced with a smaller production system, laboratory-scale system, or pilot plant that needs to be monitored and controlled. Also, your system may need to be much more flexible if it's experimental in nature. Even though your needs are different, many of the concepts and control principles you will use are the same as those used in the largest plants, making it worth your while to study their techniques.

Large process control systems generally rely on networked minicomputers with a variety of smart I/O subsystems, all using proprietary software. Until recently, most software for these larger systems was not open, meaning that the end user could not add custom I/O interfaces or special software routines nor interconnect the system with other computers. Even the smaller process control packages most of which...