Research On Detection Method Of Liquid Low Flow Using Differential-Pressure Compensation

Liquid flow is an important parameter of industry. Along with the fast development of modern industrial technology, and the measuring environment complicates day by day, the requirement of flow measurement comes higher and higher, many technical problems await to be solved, measuring precision is one of the keys. For liquid low flow measurement of volumetric flowmeter, the erroris mainly from leakage.In this thesis, the error characteristics were analyzed firstly, and a full new measuring method, differential-pressure compensation method, is arising to improve the measuring precision according to the principle of hydromechanics. And it elaborates the design idea and integrating the theory of examination and control, provides the construction of examination and test system. And then, it gives detailed illustration and design of the partials of the system, differential pressure examination and test, signal gathering and transforming, controlling method and motor driving.The function of differential pressure examination and test part is to complete the transformation from non-electric signal to electric signal. Using capacitive differential pressure transformer, the differential pressureâ–³P between entrance and exit of flowmeter is transformed to a standard electric current signal in 4~20mA for output. The function of the signal gathering and transforming is power amplifying and A/D transformation, processed by AT89C51AC2 CPU of ATMEL USA. The thesis analyses the motor driving part, by step-motor, designs the step-motor driver and its power amplifier. Moreover, the anti-jamming design guarantees the system's security and stability. The control method is the keystone in this thesis. After analyzing several regular control methods in fluid control field and contrasting their advantage and shortcoming, a new fuzzy self-adjusting PID control method, united the advantages of normal PID control and fuzzy control, comes out. It owns not only the advantages, simple structure, high precision and no error of normal PID control, but also the advantages, excellent dynamic and non-linear performance of fuzzy control. Once the variable and relation to it are made certain, the control table comes out. The simulating result by MATLAB shows the good control performance of this control system.