Research On The Pneumatic Valve Positioner Control System

Along with the computer technology entering into the late PC era and being extensively and gradually used in the process of industrial automation control, a new generation of intelligent electro-pneumatic valve positioners which are based on embeded technology begin to replace the ordinary valve positioners and become one of the leading valve controller in present industrial production. Pneumatic valve positioners hasve been widely used in industrial production on the ground of their unique advantages. Modern industrial production requires the process control more reliable, precise, high-speed and also functional and easier to use,which makes the study of the pneumatic valve positioners especially significant.Firstly, this thesis focuses on the design and study of the pneumatic valve positioner itself, mainly about the overall and detailed design of the soft and hardware of intelligent pneumatic valve positioners. Secondly, The hardware adopting high-performance 32 bits ARM processors, and the software based onμC/OS-Ⅱ—the real-time operating system of the embeded technology,achieves data acquisition, algorithm controlling, PWM output and the plan and design Human Computer Interface. Comparing and analyzing the functions of the intelligent pneumatic valve positioners home and abroad, the detailed planning and programming and debugging of intelligent pneumatic valve positioners with simple operation and complete-functions, which are required by this thesis, have been achieved.Thirdly, this thesis carries out a detailed study on the basic features of the pneumatic valve positioner control system,mainly studying the law of motion of pneumatic diaphragm control valve control system from the mechanism analysis; having deduced the mathematical model of pneumatic valve control system on the basis of some theorems and laws;calculating the steady-state force balance equation of actuators with reference to the concrete parameters of pneumatic diaphragm control valve products;having analyzed the effect and its degree of the static friction to the pneumatic control valve dead zone; approximattely calculating the parameterized dynamic state of mathematical model;and getting the main factors affecting the dynamic performance of the system from the composition of mathematical model.At last, the fifth chapter aiming at several main factors affecting the system dynamic model, with the help of the submodule of MATLAB,processes characteristic analysis and simulation to the established dynamic mathematic model system. Mainly from the aspect of system stability, simulation studies pulse cycle and sampling period. Open-loop simulation analyzes system responses to pneumatic control in different stability of psid spool to know that the system is in the oscillation segment. The bigger the differential pressure is, the bigger the damp is,and the less the oscillation is; In closed-loop, this thesis studies the tracing features of step response,sinusoidal signal,and square signal under steady air supply pressure. When air supply pressure is varying and differential pressure is affected by fluctuation, steady-state error of the system will hop.