Page 1143 - The Mechatronics Handbook

43

Control with

Embedded Computers

and Programmable

Logic Controllers

43.1 Introduction
43.2 Embedded Computers
Hardware Platforms • Hardware Interfacing •
Hugh Jack Programming Languages
43.3 Programmable Logic Controllers
Grand Valley State University
Programming Languages • Interfacing • Advanced
Andrew Sterian Capabilities
Grand Valley State University 43.4 Conclusion

43.1 Introduction
Modern control systems include some form of computer, most often an embedded computer or pro-
grammable logic controller (PLC). An embedded computer is a microprocessor- or microcontroller-
based system used for a specific task rather than general-purpose computing. It is normally hidden from
the user, except for a control interface. A PLC is a form of embedded controller that has been designed
for the control of industrial machinery. (See Fig. 43.1.)
A block diagram of a typical control system is shown in Fig. 43.2. The controller monitors a process
with sensors and affects it with actuators. A user interface allows a user or operator to direct and monitor
the control system. Interfaces to other computers are used for purposes such as programming, remote
monitoring, or coordination with another controller.
When a computer is applied to a control application, there are a few required specifications. The system
must always remain responsive and in control of the process. This requires that the control software be
real-time so that it will respond to events within a given period of time, or at regular intervals. The
systems are also required to fail safely. This is done with thermal monitoring for overheating, power level
detection for imminent power loss, or with watchdog timers for unresponsive programs.

43.2 Embedded Computers

An embedded computer is a microprocessor- or microcontroller-based system designed for dedicated
functionality in a specialized (i.e., nongeneral-purpose) electronic device. Common examples of embed-
ded computers can be found in cell phones, microwave ovens, handheld computing devices, automotive
systems, answering machines, and many other systems.

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