| Pneumatic control valve is widely used in the process industry, that contributes to itssimple and safety structure. The performance of control valve is important to the controlsystem. Because it is the most frequently used one in the control system. Stuffing box in thecontrol valve is applied to leakproof seal. On the other hand, it creates friction. The controlof valve location will deteriorate due to this friction. So, many investigators pay attention tothe research of friction and its impact on the control valve.This paper introduces the structure of the pneumatic control valve and several importantfriction phenomenon. Based on that, this article has launched a series of analysis, such as:(1) Based on the Karnopp friction modeling, the actuator modeling has been construct.Then the MATLAB/Simulink is given by to prove that, the nonlinear characteristic of controlvalve is caused by friction.(2)This article has designed a fault diagnosis system for the control valve. This systemcan obtain the deformation signal of stem, valve position signal and the gas chamber pressuresignal by its hardware, at the same time analyses the signals by the software.The experimental platform has been set up for researching valve positioning. This platformcan send a given valve position signal to the locator. Then the given signal and the feedbacksignal of valve position will been obtained and storage.(3)The indirect measurement of friction has been put forward. Based on Newton’s law,the friction is calculated by analyzing the valve position and pressure value. Then themeasurement is verified by comparing the calculated friction value to observed friction value.(4)This article has researched quantitative relation between friction and indexes of errorintegral which can evaluate of control performance. Firstly, a suitable index of error integralshould be selected by TOPSIS. Then the relationship between the selected index and frictionhas been researched. As a result, the relationship has be found by the experimental data.This dissertation is on the basis of a large number of papers, theoretical guidance, andespecially a large number of experimental results, which took almost1000hours in laboratoryand enterprises. The research achievement has been successfully used in nuclear power valveproduction companies.The innovation in this paper:1) The indirect measurement of friction has been putforward.2) Quantitative relation between friction and indexes of error integral has been found by the experimental data. Through this quantitative relation, people know not only howto deal with the parameters setting of PID in this situation but also a new research direction ofsoft-measuring for friction and fault diagnosis of control valves. |
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