Automatic control technology integrates given unit, adjusting unit, output and execution unit, measuring unit, feedback unit and so on. The basic principle is that a given unit provides a set control target, the adjustment unit compares the difference between the given and feedback signals and performs PID operation (proportion, integration and differentiation) to finally output the control signal, the output and execution unit refers to converting the previous control signal into the physical quantity of the actual equipment for output, the measurement unit detects the actual value of the physical quantity, and the feedback unit will output the detected physical quantity.

3. The conversion from physical quantity to electric quantity is completed in the measuring unit, and the conversion from electric quantity to physical quantity is completed in the output and execution unit;

4. It's a long story with examples. I'm afraid I have to give you a piece of paper. Hehe, even if you want to explain the PID regulator clearly, it will take thousands of words.

Supplement:

Each unit can find the transfer function, which requires the knowledge of Laplace transform.