The Derivative Component in PID Tuning

So what is it that derivative is supposed to help accomplish?  Most of us get by most of the time with simply using the “P” and “I” components when tuning a loop and if the loop is reasonably fast such as a flow meter or speed adjustment or even pressure we can get the job done and not have to deal with derivative. When we’re dealing with loops that have long response times such as temperature loops for tanks or dryers, there is a tendency to over-damp those loops to avoid massive overshoot of the process variable (that is if you don’t use the derivative component). If we just think about our car for a minute, let’s pretend that we are the PID loop control and the speedometer is our process variable and the speed limit (hopefully) is the setpoint. If we only use “P” to govern how we apply the accelerator then we’ll never reach setpoint because “P” needs some error in order to have an output and since this is a linear direct proportion (gain being the proportionate factor) it is also immediately …