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PID stands for Proportional, Integral, Derivative. Controllers are designed to eliminate the need for continuous operator attention. The set-point is where you would like the measurement to be. Error is defined as the difference between setpoint and measurement. (error) = (set-point) - (measurement) The variable being adjusted is called the

manipulated variable which usually is equal to the output of the controller. The output of PID controllers will change in response to a change in measurement or set-point.
Manufacturers of PID controllers use different names to identify the three modes. These equations show the relationships:
P Proportional Band = 100/gain
I Integral = 1/reset (units of time)
D Derivative = rate = pre-act (units of time)
In the following paper you will see how to tune a PID loop and see its relation in the other loops.