The Design of Intelligent Valve Displacement Transmitter Based on the Linear Hall Sensor
|School||Hangzhou University of Electronic Science and Technology|
|Course||Control Theory and Control Engineering|
|Keywords||Smart Transmitter Positioner Non-contact Displacement measurement|
Three aspects of industrial process automation - process parameters detection, calculation and control, regulation and enforcement are completed by instrumentation, DCS control system, actuators, three types of industrial automation instruments, and basic equipment known as the three major industrial automation , the technology level has become one of the decisive factors of the process of industrial development, a profound impact on the quality of the production, efficiency, safety, and environmental protection. As the main control valve actuator by regulating media flow to control the process parameters, the entire automation system must end executive instrument, adjust the pros and cons of the quality control system, has great impact on safe and stable operation. Technical level of domestic actuator is very backward, has become the bottleneck of the development of automation technology, domestic demand for high-end smart actuators is almost entirely dependent on imports, has caused the state attaches great importance. There is an important problem in the control of the actuator, the stem displacement i.e. the precise real-time measurement of the valve position. Actuators installed on the site of the industrial production, often work in vibration, high temperature and other harsh outdoor environment, travel and frequent anti-stroke movement, and the valve and actuator model specifications required valve position measurement range, so it is necessary to study develop a common valve position measuring device that is smart valve position transmitter. It must meet the following requirements: (1) non-contact, that is between the valve position transmitter and the actuator stem connection to isolate the scene environment and to no wear and anti-interference ability; (2) a large number of process to achieve from 0 to 160mm measuring range, in order to adapt to a variety of types and specifications of actuator applications; (3) low-power, due to The standard measurement transducer request gets its power from the loop, including the sensor transmitter must be low power consumption; ④ high precision and low price standard transmitter, using the standard 4 ~ 20mA loop signal output, which makes a variety of instruments and device compatibility and interchangeability. At present, many foreign companies have been launched smart valve position transmitter, while China is still blank in this regard, research and development of intelligent transmitter is of great significance. The main content of this topic is to study the design of a smart valve position transmitter meet the above requirements. The valve position transmitter main role is to measure the valve actuator stem moves up and down displacement, after a non-linear processing to calculate the percentage of the displacement, and converted into a standard 4 ~ 20mA loop current output. Mainly to complete the following tasks: 1. Sensors, transmitters and smart transmitters characteristics and course of development; analysis of the working principle of the valve positioner; explore several common displacement measurement method, the ultimate combination of this topic the practical application of choice of linear Hall sensor as a non-contact displacement measurement sensor A1391 study in detail the working principle of the linear Hall sensor chip A1391, recommended conventional linear measurement solutions, and to design the two new measurement program, according to the requirements of the subject and the actual application requirements analysis to determine a self-designed nonlinear measurement solutions, design a set of measuring mechanism, and details the measurement principles and methods of the agency. On the basis of in-depth analysis of the measurement principle independent design intelligent valve position transmitter. The transmitter includes both software and hardware. The hardware signal amplification, A / D, D / A conversion, software sampling, non-linear processing, calculated as a percentage of valve position and LCD. In this thesis, the smart valve position transmitter hardware design to meet the low power requirements, each part of the circuit are given a specific method, problems that need attention; in-depth study of the different valve position the percentage of different theoretical calculation method, write code to achieve the calculation of the percentage of valve position; using regular sampling, making the whole system in real-time detection of valve position; Finally, in order to facilitate the observation, this percentage of the signal sent to the LCD display, and convert into unified industry standard 4 ~ 20mA loop current output. The final test results show that this thesis can be more accurate measurement of the actuator valve position is calculated and displayed, and can be used for other non-contact measurement of the displacement. In this paper, the design of smart transmitters and the key technology and innovation: (1) design of a novel magnetic steel structure, magnetic field distribution of the law; (2) non-linear distribution of the magnetic field sine fitting, linear Hall sensor non- linear measurement; (3) to overcome the installation location to the measurement error caused by the adaptive function of the transmitter; (4) two-wire transmitter position signal voltage isolation solutions.