With control systems we can move large equipment with precision that would otherwise be impossible.
We can point huge antennas toward the farthest reaches of the universe to pick up faint radio signals; controlling these antennas by hand would be impossible.
Because of control systems, elevators carry us quickly to our destination, automatically stopping at the right floor.
We alone could not provide the power required for the load and the speed; motors provide the power, and control systems regulate the position and speed.
We build control systems for four primary reasons:
- Power amplification
- Remote control
- Convenience of input form
- Compensation for disturbances
For example, a radar antenna, positioned by the low-power rotation of a knob at the input, requires a large amount of power for its output rotation.
A control system can produce the needed power amplification, or power gain-Robots designed by control system principles can compensate for human disabilities.
Control systems are also useful in remote or dangerous locations. For example, a remote-controlled robot arm can be used to pick up material in a radioactive environment.
Control systems can also be used to provide convenience by changing the form of the input. For example, in a temperature control system, the input is a position on a thermostat. The output is heat.
Thus, a convenient position input yields a desired thermal output. Another advantage of a control system is the ability to compensate for disturbances.
Typically, we control such variables as temperature in thermal systems, position and velocity in mechanical systems, and voltage, current, or frequency in electrical systems.
The system must be able to yield the correct output even with a disturbance. For example, consider an antenna system this point in a commanded direction.
If wind forces the antenna from its commanded position, or if noise enters internally, the system must be able to detect the disturbance and correct the antenna's position.
Obviously, the system's input will not change to make the correction.
Consequently, the system itself must measure the amount that the disturbance has repositioned the antenna and then return the antenna to the position commanded by the input.