Abstract: In order to study the application of cascade Pl controller in DCS, a self-defined user funetionblock based on ABB -800F software is selected as the research object, and the software comes with itsown PlD universal continuous adjustment control block(CCU), expand the PlD controller panel andprogram design , enhance its function, unlock through password. It realizes a general PlD soft regulatoiwhich can adjust and debug parameters intuitively in graphical interface. It can realize single loop Plcontrol and cascade PID control, and can be used in programming configuration like FBD instruction.'This user funetional block cascade Pll soft regulator has achieved good results through application in theproduction of formaldehyde in a chemical industry, and has the value of reference and promotion.

Key words: user function block, cascade PID controller, parameter setting