19.2 CONTROL SYSTEMS

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Control systems use some output state of a system and a desired state to make control decisions.

In general we use negative feedback systems because,

- they typically become more stable

- they become less sensitive to variation in component values

- it makes systems more immune to noise

Consider the system below, and how it is enhanced by the addition of a control system.

Figure 19.1 An example of a feedback controller

Figure 19.2 Rules for a feedback controller

Some of the things we do naturally (like the rules above) can be done with mathematics

19.2.1 PID Control Systems

The basic equation for a PID controller is shown below. This function will try to compensate for error in a controlled system (the difference between desired and actual output values).

Figure 19.3 The PID control equation

The figure below shows a basic PID controller in block diagram form.

Figure 19.4 A block diagram of a feedback controller

The PID controller is the most common controller on the market.

19.2.2 Analysis of PID Controlled Systems With Laplace Transforms

19.2.3 Finding The System Response To An Input

Even though the transfer function uses the Laplace `s', it is still a ratio of input to output.

Find an input in terms of the Laplace `s'

19.2.4 Controller Transfer Functions

The table below is for typical control system types,