Detection of sluggish control loops-experiences and improvements

An appealing index for detection of sluggish control loops has been proposed by Hägglund (Control Eng. Practice 7 (1999) 1505). When dealing with real, noisy data, however, the index value depends heavily on the data pre-treatment. This paper describes ways to compute the Idle Index under realistic conditions. Examples are shown and additional problems that might occur are discussed. Furthermore, the case of non-stepwise disturbances is discussed.