You want to keep some variable (say: temperature) constant. At the same time external factors
are causing it to change (cold from the outside). There is a way (a heater) to influence the
variable. Now all you need to do is determine when to use it to keep the variable constant.
The Process is any process that affects the Controlled Variable.
The Controller can be any subsystem that has both knowledge of the influence of the Input Variables and the effect of changing the Manipulated Variables on the Controlled Variables.
Where does it come from?
Process Control is an engineering disipline. It has a long history.
When should you use it?
Use such an architecture when there is something to be controlled and you have a number of outside factors disturbing it.
How does it work?
Process Control architectures have some variations. They can be either Open Loop or Closed Loop. The Closed Loop systems can be either Feedback systems or Feedforward systems.
Open Loop systems just perform a function on on the Input Variables to determine how to control the process.
Picture: Open Loop
Feedback Closed Loop systems measure changes in the Controlled Variable directly, and feed them back as Input Variables into the Controller.
Picture: Feedback Closed Loop
Feedforward Closed Loop systems do not measure changes in the Controlled Variable directly, because they the Controlled Variable is not affected immediately, or because the Controlled Variable cannot be measured directly. In stead, variables named Intermediate Variables that are indications of the Controlled Variable are fed back as Input Variables.
Picture: Feedforward Closed Loop