Process Time Lags:

In the last instance, the control of the lube oil temperature might initially seem simple. Apparently, the operator need only measure the lube oil temperature, compare the actual temperature to the desired (setpoint), compute the amount of error (if any), and adjust the temperature control valve to correct the error accordingly. Therefore, processes have the features of delaying and retarding changes in the values of the process variables.  These features greatly raise the difficulty of control.

Process time lags are the common term which describes these procedure delays and retardations. Procedure  time  lags  are  caused  through  three  properties of the process. They are: resistance, capacitance, and transportation time.