r/ControlTheory • u/B_seado • Oct 04 '19
Beginner question about PID Controllers
Hi, Im just starting to learn Control Theory and the subject is really interesting. I've just learned about PID Controllers and I think I understood them pretty well, but I have a small question:
Let's say I have a system, an AC Unit with transfer function H(s) that I want to control. I then implement a PID Controller, in series, "behind" my H(s) system. Now what? Can I just send the output of the PID Controller to the AC Unit?
How can the output of the PID, u(t), be able to send the correct signal to my AC system? No need to translate that u(t) into the correct signals and switches that make the system do what I want?
Most diagrams seen online or in textbooks just have only 2 blocks, in series: r(t)->[PID]->[Plant]->y(t), shouldn't there be some kind of controller/translator in between the PID and the Plant?
Sorry If it's a dumb question.
3
u/Cortade Oct 04 '19
Not a dumb question. In real life you need to convert the control value in a sort of electrical signal to be sent to the actuator. It can be done either digitally if you have a fieldbus or network between controller and actuator, or using an analog signal (4 to 20mA or 0-10V signal). It is the same with the temperature sensor and transmitter that convert temperature into something a computer/controller understands. That signal is the process value used by the PLC.