Fault Diagnosis For Headbox Control System Of Paper Machine

At present, the paper industry has been developing rapidly to meet thepeople’s fast expanding demand for paper product. At the same time,paper-making equipment shows the characters and trends of large-scale,integrated, and continuous. These improvements promote and play a key role inthis growing process. Paper making process is more and more dependent on theautomatic control system to make operation and management. In this case, theapplication of automation system makes the paper industry can be more effectivecontrolling and monitoring, but it also greatly increases complexity of the wholesystem. In order to avoid system fault caused variety losses, paper industrylargely increased stability requirements for the control system. Therefore, faultdiagnosis technology has become an important part of control system researchand an indispensable part of industrial process control.As a very important equipment of the paper industry, headbox connect theshort circulation system and form section of paper machine. It has many factorsto influence the quality of the paper quality. Headbox control system must acceptthe measured or command signal from QCS at end paper to make accordinglycontrol. It needs the cooperation of DCS, QCS and MCS at the same time. If thefailure happened, system need to quickly identify the fault type, location andtake effective measures returned to normal as soon as possible.This paper focuses on the headbox control system fault diagnosis andimplementation issues. The main work is following.Firstly, this paper introduces the control system of hydraulic air-cushionedheadbox with dilution water, including its total pressure level control, dilutionwater circulation, edge flow control and other factors. Especially, it focused onthe dilution water valve actuator control, including the running principle, control parameters, calibration and clean process. Then, it listed the headbox controlsystem hardware components and the system fault.Secondly, it introduced the basic principles and diagnosis methods,especially focused on expert systems. It used fault tree analysis to build headboxcontrol system fault tree.Thirdly, the paper gave a detailed description of the fault diagnosistechnology. It analysised fault type of DCS and PLC systems, and proposed CFC,faceplate tools and function blocks for control loop failure monitoring anddiagnostic methods in the SIMATIC PCS7system; used of STEP7call errorhandling OB for fault diagnosis; programed in the corresponding subprogram forexternal device fault diagnosis.Finally, in the realization of the paper machine headbox control system faultdiagnosis, the whole system is divided into the field level, control diagnosticlayer and remote diagnostic layer. It solved the problem of communicationbetween the layers, and achieved fault-recognition software, database creationand upgrade, remote diagnostics and archiving and printing of diagnostic resultsusing WinCC monitoring system.