Theory

A PID controller tries to minimize the error between measured variable and the setpoint by calculating the error and then taking a suitable corrective action. Note that the output of interest is called the measured variable or process variable, the difference between the setpoint and the measured variable is called the error and the control action taken to minimize the error is given as input to the process in the form of the manipulated variable. A PID controller does not simply add or subtract the error in order to calculate control action but instead uses three distinct control features, namely, Proportional, Integral and Derivative. Thus, a PID controller has three separate parameters.