Design On Intelligent Valve Positioner

Intelligent valve positioner assists the valve to achieve flow control, so it plays a crucial role in the field of industrial control. Intelligent Valve Positioner can self-tuning the parameters of the valve through the operation of automatic adjustment or initialization such as direction of implementing agencies, the zero point and stroke range. Intelligent valve positioner is used in different types of valve to overcome the suffered friction and unbalanced force of stem. The core of the valve can be achieved accurate positioning according to the setting signal of user. The intelligent valve positioner improves positioning accuracy and linearity.This paper focuses on the pneumatic valve positioner. The main tasks of this paper include three aspects:hardware and software design and optimization, control algorithm research and test, propose a method to achieve flow characteristics. The specific work are as follows:1. This paper insights into the principle of intelligent valve positioner and analysis the main components of the control system especially piezoelectric valve and position sensor. The principle of piezoelectric valve is studied and driving experiments based on PWM are finished. The position sensor use conductive plastic precision rotary potentiometer. The detection and calibration of position sensor are completed to get the relationship between the AD value and stem displacement. The valve position feedback nonlinear correction is needed when the executing agency is straight-line travel.2. The hardware board is the main component of intelligent valve positioner. The design and improvement of the hardware circuit are completed using LPC2290as microprocessor. The tasks include the allocation of microprocessor I/O resources, the design of power circuit, I/V conversion circuit, AD sampling, piezoelectric valve driving circuit, detection circuit of valve position feedback signal serial communication circuit, button and LCD display circuit. The hardware board is tested and the shortcomings of the hardware circuit are improved and optimized so that the hardware board can work more stable and reliable. Based on hardware circuit, software design and basic driver programs are finished. The planning and priority arrangements of tasks are carried out in μcosⅡ operating system. Finally, the software programs are completed.3. The control algorithm is the core of software control system. The open-loop characteristic experiments that driving piezoelectric valve based on PWM are finished to get minimum PWM duty cycle in inlet and outlet status. According to characteristics of valve, control algorithm including improvement for five-step control, PID, Bang-Bang PID, self-tuning PID are studied and tested. Finally, the self-tuning PID is applied into intelligent valve positioner.4. The positioner is used to precisely position the valve by filling or venting the actuator with the corresponding amount of air. As one of the main attachment of the valve, the positioner assists the valve to achieve flow control. This paper analysis the flow characteristics and propose a method to achieve different type of flow characteristics.