In order to measure the process variable (i.e., temperature), a sensor is used (let us say an RTD).Ī set point is the desired response of the process. Assume that the process variable is temperature (in centigrade). It also accepts the desired actuator output, which is referred as set variable, and then it calculates and combines the proportional, integral and derivative responses to compute the output for the actuator.Ĭonsider the typical control system shown in above figure in which the process variable of a process has to be maintained at a particular level. It gets the input parameter from the sensor which is referred as actual process variable.
