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1. The Excitement of Control Engineering

1.5.5 Communications

Interconnecting sensors to actuators involves the use of communication systems. A typical plant can have many thousands of separate signals to be sent over long distances. Thus, the design of communication systems and their associated protocols is an increasingly important aspect of modern control engineering.

There are special issues and requirements for communication systems with real-time data. For example, in voice communication, small delays and imperfections in transmission are often unimportant by virtue of being transparent to the recipient. However, in high-speed real-time control systems, these issues could be of major importance. For example, there is an increasing tendency to use Ethernet-type connections for data transmission in control. However, as is well known by those familiar with this technology, if a delay occurs on the transmission line, then the transmitter simply tries again at some later random time. This obviously introduces a non-deterministic delay into the transmission of the data. All control systems depend upon precise knowledge of, not only what has happened, but when it happened, so attention to such delays is very important for the performance of the overall system.