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then was to put multiple mechanical control systems in with interlocks as needed.
Failure meant explosion!
The speed governor in Figure 2-29 is a great example of a mechanical engineer used
to solve a control system problem. It regulates the speed of an engine. As the engine
speed increases, the two metal globes spin around the vertical shaft. Since the outward
centrifugal force increases, the globes start to move outward, pulling on the diagonal
struts. The diagonal struts, if pulled hard enough, will pull up the base and release some
steam pressure. This keeps the engine from going too fast. It’s a good example of a sep-
arate control system for velocity. School buses still have such mechanisms on their
engines if you look carefully. But better ask permission before snooping around!
A nice example of a governor design can be found at www.usgennet.org/usa/topic/
steam/governor.html. A few years later, engineers began to think about centralizing con-
trol systems. Computer electronics facilitated this transition since all the information
could easily be gathered in one place and manipulated. The engineers cast about for a
way to control multiple variables at the same time and raised several key questions:
How would a multiple variable system be designed? What framework would it
have?
How many variables could be controlled at the same time?

FIGURE 2-29 The speed governor is a venerable mechanical feedback
control system.