On-line Detection Of Stiction Based On DCS

The control systems in the process industry are essentially nonlinear,and the linear object is few, the nonlinear process is researched as the linear process.According to statistics,about 30%of the control loops in the process industry are in a state of oscillation,in which 1 / 3 due to the valve stiction. Therefore,stiction is the most common problems in the industrial control process,and its existence serious impacts on the performance of the control system.On-line detection ofstiction is very important to improve the accuracy and stability of the control loops.But there are a few studies in the related fields so far,in recent years,some foreign researcheres present different kinds of theories and methods of the stiction on-line detection,but these theories and methods have one or more limitations in the areas such as speed,accuracy,simpleness and so on, which limits the application of these theories and methods.Aiming at the oscillation problem of control loops in the process industry,this paper focuses on studying the impact of valve stiction,mainly resolves the solution of modeling valve stiction system and on-line detection of stiction.Using the operate data of closed control loops and the relevant theories and technique of identification to identify the existence of the valve stiction in the control loops.The new method can not only detect the existence of stiction,but also identify the process model at the same time,is very suitable for founding the specific reason of oscillation.Based on the analysis of the stiction models and on-line detection methods which established by foreign researcheres,this paper presents a new stiction model which can comparative accurately reflect the true characteristics of the valve and is suitable for on-line detection,studies an advanced on-line detection method based on system identification.This method identifies the existence of the valve stiction in control loops by using the data of the controller output and the process value and least-squares method.According to this new method of stiction detection,this paper achieves the system software of advanced on-line stiction detection by using MATLAB GUI to design graphical user interface.The sample data of control loops can be acquired from Text or Excel,or from DCS configuration software directly through OPC communication by the system software,and these data can be transformed into wave pictures,and used for on-line detection and analysis of stiction.The quantitative results of stiction can be displayed by the system software. This paper does the simulation analysis of the established stiction model and detection method by using MATLAB software,and use the system software of advanced on-line stiction detection to detect the valve stiction in control loops of real DCS pharmaceutical project.The results of simulation and practical application show the reasonableness of the stiction model and the effectiveness and accuracy of the detection method.The results of research in this paper can not only be used to detect the reason of control loop oscillation in the process industry,but also improve the product quality,reduce energy consumption and maintain the stability of the process,as well as reduce the intensity of the operation,and so on. The research of stiction detection can not only fill in the gaps in the field of our country,but also significantly increase the economic efficiency of the process industry with its broad and huge prospect of application.