If our errors large, we’ll get a large control signal if our errors are small. It’s quite apparent why this is known as proportional control because with a fixed Kp constant the control signal is proportional to the error. Since all the P controller does is multiply the error by the control constant Kp. So let’s say we have a positive step change in the setpoint and therefore we get a positive error. Now lets see how a closed loop system performs with just proportional control. But in order to understand the advantage and disadvantage of using one or more term, we will break down the controllers operation by dealing with each term separately. As you see in block diagram of PID controller, the error essentially goes through each PID block and their outputs are summed up and form a control signal that drives the process to the desired setpoint.
Now I will discuss P or proportional term of the PID controller.
