With derivative control, the controller produces a control action that is
proportional to the rate at which the error is changing. Derivative control
is not used alone but always in conjunction with proportional control
and, often, integral control. Figure 7.32 shows the basic form of a
proportional plus derivative controller. The proportional element has an
input of the error e and an output of Kpe. The derivative element has an
input of e and an output which is proportional to the derivative of the
error with time, i.e.