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1. The Excitement of Control Engineering

1.5.6 Computing

In modern control systems, the connection between sensors and actuators is invariably made via a computer of some sort. Thus, computer issues are necessarily part of the overall design. Current control systems use a variety of computational devices including DCS's (Distributed Control Systems), PLC's (Programmable Logic Controllers), and PC's (Personal Computers). In some cases, these computer elements are rather limited with respect to the facilities they offer. As with communication delays, computational delays can be crucial to success or failure in the operation of control systems. Determinism in timing is important, so a multi-tasking real-time operating system may be required.

Another aspect of computing is that of numerical precision. We know of several control systems that failed to meet the desired performance specifications simply because of inadequate attention to numerical issues. For this reason, we will devote some attention to this issue in the sequel.

A final computer-based question in control concerns the ease of design and implementation. Modern computer-aided tools for rapid prototyping of control systems provide integrated environments for control-system modeling, design, simulation and implementation. These pictures to real-time code facilities have allowed development times for advanced control algorithms to be reduced from many months to periods on the order of days or, in some cases, hours.